JP2019035141A - Method of enhancing moldability of magnesium alloy - Google Patents
Method of enhancing moldability of magnesium alloy Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
- C22F3/00—Changing the physical structure of non-ferrous metals or alloys by special physical methods, e.g. treatment with neutrons
- C22F3/02—Changing the physical structure of non-ferrous metals or alloys by special physical methods, e.g. treatment with neutrons by solidifying a melt controlled by supersonic waves or electric or magnetic fields
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- C22C23/00—Alloys based on magnesium
Abstract
Description
本発明は、マグネシウム合金の成形性増加方法に係り、より詳細には、マグネシウム合金の引張成形中にパルス電流を印加して、成形性を増加させるマグネシウム合金の成形性増加方法に関する。 The present invention relates to a method for increasing the formability of a magnesium alloy, and more particularly to a method for increasing the formability of a magnesium alloy by applying a pulse current during tensile forming of the magnesium alloy to increase the formability.
マグネシウムは、比重が１．７４と軽いが、単位重量当たり強度は非常に大きいために、自動車や航空機の軽量構造部品として使われている。それだけではなく、振動吸水性、電磁波遮蔽性のような特性に優れて、スポーツ用品、電子機器、通信機器分野で需要が増加しており、最近、インプラント用の生体材料も開発されている。しかし、マグネシウムは、軟性が低くて、常温加工が困難であり、加工時に集合組織が形成されて、成形性が不良であるために、用途が制限されている。したがって、マグネシウム合金の成形性の改善のために、高成形性新合金の設計、結晶粒の微細化を通じた成形性の改善、加工熱処理を通じた集合組織の緩和、超塑性成形技術、集合組織制御圧延技術などを積極的に開発している。 Magnesium has a light specific gravity of 1.74, but its strength per unit weight is so high that it is used as a lightweight structural component for automobiles and aircraft. In addition, it has excellent properties such as vibration absorption and electromagnetic wave shielding, and demand is increasing in the field of sports equipment, electronic equipment and communication equipment, and recently biomaterials for implants have also been developed. However, magnesium has low flexibility and is difficult to process at room temperature, and a texture is formed at the time of processing, and its formability is poor, so its use is limited. Therefore, in order to improve the formability of magnesium alloys, the design of new alloys with high formability, the improvement of formability through grain refinement, the relaxation of texture through thermomechanical treatment, the superplastic forming technology, the texture control We are actively developing rolling technology.
このような状況で、既存のマグネシウム合金の成形性増加のための方法として、温間成形、漸進成形（ｉｎｃｒｅｍｅｎｔａｌ ｆｏｒｍｉｎｇ）またはレーザビーム成形（ｌａｓｅｒ ｂｅａｍ ｆｏｒｍｉｎｇ）技術が使われているが、高温成形及び誘導加熱工程は、高コスト、材料の熱勾配、ダイ接着及び表面酸化の問題が発生する。特に、レーザビーム成形は、製造工程で過度な時間とコストとを必要とする限界を有している。 In this situation, warm forming, incremental forming or laser beam forming techniques are used as methods for increasing the formability of existing magnesium alloys. The induction heating process has problems of high cost, material thermal gradient, die adhesion and surface oxidation. In particular, laser beam shaping has limitations that require excessive time and cost in the manufacturing process.
本発明は、前記問題点を含んで多様な問題点を解決するためのものであって、マグネシウム合金の引張成形中にパルス電流を印加して、成形性を増加させるマグネシウム合金の成形性増加方法を提供することを目的とする。 The present invention is for solving various problems including the above-mentioned problems, and is a method for increasing formability of a magnesium alloy by applying a pulse current during tensile forming of the magnesium alloy to increase formability. The purpose is to provide.
しかし、このような課題は、例示的なものであって、これにより、本発明の範囲が限定されるものではない。 However, such a problem is exemplary and does not limit the scope of the present invention.
前記課題を解決するための本発明の一観点によれば、（ａ）マグネシウム合金に応力（ｓｔｒｅｓｓ）を印加する段階と、（ｂ）前記応力を印加している最中に、前記マグネシウム合金に少なくとも１回のパルス電流（ｐｕｌｓｅｄ ｅｌｅｃｔｒｉｃ ｃｕｒｒｅｎｔ）を印加する段階と、を含むマグネシウム合金の成形性増加方法が提供される。 According to one aspect of the present invention for solving the above problems, (a) applying stress to the magnesium alloy; and (b) applying the stress to the magnesium alloy during the application of the stress. Applying at least one pulsed electric current, and providing a method for increasing the formability of the magnesium alloy.
また、本発明の一実施例によれば、前記マグネシウム合金は、ＡＺ３１−圧延材、ＡＺ３１−焼鈍材またはＡＺ９１であり得る。 According to another embodiment of the present invention, the magnesium alloy may be AZ31-rolled material, AZ31-annealed material, or AZ91.
また、本発明の一実施例によれば、前記（ａ）段階で、前記応力の方向は、前記マグネシウム合金の圧延が形成された方向と平行であり得る。 According to an embodiment of the present invention, in the step (a), the direction of the stress may be parallel to a direction in which the magnesium alloy is rolled.
また、本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流の最初のパルス電流を前記マグネシウム合金の降伏強度（Ｙｉｅｌｄ ｓｔｒｅｎｇｔｈ）地点、塑性区間（Ｐｌａｓｔｉｃ ｒｅｇｉｏｎ）または最大引張強度（Ｕｌｔｉｍａｔｅ ｔｅｎｓｉｌｅ ｓｔｒｅｎｇｔｈ）地点で印加することができる。 In addition, according to an embodiment of the present invention, in the step (b), the first pulse current of the pulse current is changed to a yield strength point, a plastic region, or a maximum tensile strength of the magnesium alloy. It can be applied at the point (Ultimate tensile strength).
また、本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流を３回印加することができる。 According to an embodiment of the present invention, the pulse current can be applied three times in the step (b).
また、本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流は、一定の電流密度（ρｉ）で印加される。 According to an embodiment of the present invention, in the step (b), the pulse current is applied at a constant current density (ρ i ).
また、本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流の電流密度は、少なくとも１００Ａ／ｍｍ２以上であり得る。 According to an embodiment of the present invention, in the step (b), the current density of the pulse current may be at least 100 A / mm 2 or more.
また、本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流の電流印加周期（ｔｐ）は、１８秒〜２２秒であり、電流印加時間（ｔｄ）は、０．４秒〜０．６秒であり得る。 According to an embodiment of the present invention, in the step (b), the pulse current application period (t p ) is 18 seconds to 22 seconds, and the current application time (t d ) is 0. .4 seconds to 0.6 seconds.
また、本発明の一実施例によれば、前記パルス電流を印加すれば、前記マグネシウム合金で再結晶速度が増加する。 Also, according to an embodiment of the present invention, when the pulse current is applied, the recrystallization rate is increased in the magnesium alloy.
また、本発明の一実施例によれば、前記マグネシウム合金は、延伸率が０．１８〜０．４１であり得る。 According to another embodiment of the present invention, the magnesium alloy may have a draw ratio of 0.18 to 0.41.
また、本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流を前記最大引張強度地点で印加する時、少なくとも８０％の延伸率が向上する。 According to an embodiment of the present invention, when the pulse current is applied at the maximum tensile strength point in the step (b), the stretch ratio is improved by at least 80%.
また、本発明の一実施例によれば、前記マグネシウム合金は、焼鈍（ａｎｎｅａｌｉｎｇ）処理しないこともある。 In addition, according to an embodiment of the present invention, the magnesium alloy may not be annealed.
前記のようになされた本発明の一実施例によれば、マグネシウム合金の引張成形中にパルス電流を印加して、成形性を増加させるマグネシウム合金の成形性増加方法を提供することができる。 According to the embodiment of the present invention as described above, it is possible to provide a method for increasing the formability of a magnesium alloy by applying a pulse current during tensile forming of the magnesium alloy to increase the formability.
もちろん、このような効果によって、本発明の範囲が限定されるものではない。 Of course, the scope of the present invention is not limited by such effects.
後述する本発明についての詳細な説明は、本発明が実施される特定の実施例を例示として図示する添付図面を参照する。これら実施例は、当業者が本発明を十分に実施可能なように詳しく説明される。本発明の多様な実施例は、互いに異なるが、互いに排他的である必要はないということを理解しなければならない。例えば、ここに記載されている特定の形状、構造及び特性は、一実施例に関連して、本発明の精神及び範囲を外れずに、他の実施例として具現可能である。また、それぞれの開示された実施例内の個別構成要素の位置または配置は、本発明の精神及び範囲を外れずに、変更可能であるということを理解しなければならない。したがって、後述する詳細な説明は、限定的な意味として取ろうとするものではなく、本発明の範囲は、適切に説明されるならば、その請求項が主張するものと、均等なあらゆる範囲と共に、添付の請求項によってのみ限定される。図面で類似した参照符号は、多様な側面にわたって同一または類似の機能を称し、長さ及び面積、厚さなどとその形態は、便宜上、誇張されて表現されることもある。 The following detailed description of the invention refers to the accompanying drawings that illustrate, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in detail to enable those skilled in the art to fully practice the invention. It should be understood that the various embodiments of the present invention are different from each other but need not be mutually exclusive. For example, the specific shapes, structures, and characteristics described herein can be embodied in other embodiments without departing from the spirit and scope of the invention in connection with one embodiment. It should also be understood that the location or arrangement of the individual components within each disclosed embodiment can be changed without departing from the spirit and scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention, if properly described, is intended to be what is claimed by the claims, and all equivalents thereof. Limited only by the appended claims. The same reference numerals in the drawings denote the same or similar functions across various aspects, and the length, area, thickness and the like may be exaggerated for convenience.
以下、当業者が本発明を容易に実施させるために、本発明の望ましい実施例に関して添付図面を参照して詳しく説明する。 Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention.
＜パルス電流印加引張成形＞
図１及び図２を参照して、パルス電流印加引張成形について説明する。
<Pulsed current applied tensile molding>
With reference to FIGS. 1 and 2, the pulse current application tension forming will be described.
図１は、本発明の一実施例によるパルス電流印加引張成形用装置を示す概略図である。 FIG. 1 is a schematic view showing an apparatus for tension forming by applying a pulse current according to an embodiment of the present invention.
マグネシウム合金の引張成形時に、パルス電流印加の影響分析のための装置であって、パルス電流を印加しながら、引張成形可能な実験装置を構成する。図１に示したように、引張成形のための試片１０をローディング（ｌｏａｄｉｎｇ）し、矢印方向に引張力を印加することができる。 An apparatus for analyzing the influence of applying a pulse current during tensile forming of a magnesium alloy, and constituting an experimental apparatus capable of performing tensile forming while applying a pulse current. As shown in FIG. 1, a specimen 10 for tensile molding can be loaded and a tensile force can be applied in the direction of the arrow.
パルス電流は、抵抗溶接機に基づいて製作された直流電源発生装置を利用し、試片１０に電流を周期的に印加させる。この際、試片１０に流れる電流と引張機との間の絶縁のために、引張機の試片１０が挟まれるジグにベークライト（ｂａｋｅｌｉｔｅ）を用いて絶縁システム（ｉｎｓｕｌａｔｏｒ）Ｉを構築する。また、電源装置で発生した直流電流が、試片１０にのみ流れるようにする。 The pulse current is applied to the specimen 10 periodically by using a direct current power generation device manufactured based on a resistance welder. At this time, in order to insulate between the current flowing in the specimen 10 and the tension machine, an insulation system I is constructed by using a bakelite on a jig between which the specimen 10 of the tension machine is sandwiched. Further, the direct current generated in the power supply device is allowed to flow only in the specimen 10.
図２は、本発明の一実施例によるパルス電流の印加条件を示すグラフである。パルス電流印加引張成形時に、パルス電流は、電流密度（ρ、単位：Ａ／ｍｍ２）、電流印加時間（ｄｕｒａｔｉｏｎ、ｔｄ、単位：秒）及び電流印加周期（ｐｅｒｉｏｄ、ｔｐ、単位：秒）を一定に設定して試片に印加することができる。図２のｔｄは、電流印加時間を意味し、ｔｐは、電流印加周期を意味する。この際、電流密度（ρ０）は、試片の初期断面積を基準にした値であり、これは、実験が進行する間に、一定の値の電流（Ａ）が印加されたことを意味する。これとは異なって、電流密度（ρｉ）は、引張成形進行時に、減少する試片の断面積を考慮して電流を変化させながら印加して、電流密度を一定に保持することができる。 FIG. 2 is a graph showing application conditions of a pulse current according to an embodiment of the present invention. At the time of pulse forming by applying a pulse current, the pulse current includes a current density (ρ, unit: A / mm 2 ), a current application time (duration, t d , unit: second) and a current application cycle (period, t p , unit: second). ) Can be set constant and applied to the specimen. T d of FIG. 2 means a current application time, t p denotes the current application period. At this time, the current density (ρ 0 ) is a value based on the initial cross-sectional area of the specimen, which means that a constant value of current (A) was applied while the experiment proceeded. To do. In contrast, the current density (ρ i ) can be applied while changing the current in consideration of the reduced cross-sectional area of the specimen when the tensile molding proceeds, so that the current density can be kept constant.
パルス電流印加引張成形で、試片の物性変化を測定するためのデータ測定システムについて説明する。試片の変形率を測定する時、一般的に使われる接触式ストレインゲージは、絶縁の問題で使用が不可能である。したがって、非接触式で試片の変形率を測定することができるイメージ基盤のデジタル画像相関法（ｄｉｇｉｔａｌ ｉｍａｇｅ ｃｏｒｒｅｌａｔｉｏｎ ｓｙｓｔｅｍ、ＤＩＣ ｓｙｓｔｅｍ）を用いて試片の長手方向の変形率を測定した。また、パルス電流印加によって発生する抵抗熱の発生を分析するために、ｋ型熱電対（ｋ−ｔｙｐｅ ｔｈｅｒｍｏｃｏｕｐｌｅ）と、熱画像カメラ（ＩＲ ｃａｍｅｒａ）と、を用いて試片の温度を測定した。 A data measurement system for measuring changes in physical properties of a specimen by pulse current application tension molding will be described. When measuring the deformation rate of a specimen, a commonly used contact strain gauge cannot be used due to insulation problems. Therefore, the deformation ratio in the longitudinal direction of the specimen was measured using an image-based digital image correlation system (DIC system) that can measure the deformation ratio of the specimen in a non-contact manner. Moreover, in order to analyze the generation | occurrence | production of the resistance heat which generate | occur | produces by pulse current application, the temperature of the test piece was measured using the k-type thermocouple and the thermal image camera (IR camera).
次いで、本発明の一実施例によるマグネシウム合金の成形性増加方法について説明する。 Next, a method for increasing the formability of a magnesium alloy according to an embodiment of the present invention will be described.
本発明によるマグネシウム合金の成形性増加方法は、（ａ）マグネシウム合金に応力を印加する段階と、（ｂ）応力を印加している最中に、マグネシウム合金に少なくとも１回のパルス電流を印加する段階と、を含むことを特徴とする。 The method for increasing the formability of a magnesium alloy according to the present invention comprises (a) applying a stress to the magnesium alloy, and (b) applying at least one pulse current to the magnesium alloy during the application of the stress. A stage.
図３は、本発明の一実施例によるパルス電流印加引張成形用試片を示す概略図である。図３のａは、試片の全長を、ｂは、試片の標点距離を、ｃは、試片の縦長を、ｄは、試片の断片長を意味する。ＲＤ（ｒｏｌｌｉｎｇ ｄｉｒｅｃｔｉｏｎ）は、試片での圧延方向を意味する。 FIG. 3 is a schematic view showing a specimen for tensile forming by applying a pulse current according to an embodiment of the present invention. In FIG. 3, a is the total length of the specimen, b is the gauge distance of the specimen, c is the longitudinal length of the specimen, and d is the fragment length of the specimen. RD (rolling direction) means the rolling direction of the specimen.
（ａ）段階で、図３に示された引張成形用試片１０を図１の引張成形用装置にローディングして引張力を印加する。図３の引張成形用試片１０は、ＲＤ方向に圧延が形成されており、それと平行方向に引張力を印加することができる。 In step (a), the tensile molding specimen 10 shown in FIG. 3 is loaded onto the tensile molding apparatus of FIG. 1 and a tensile force is applied. 3 is rolled in the RD direction, and a tensile force can be applied in the direction parallel thereto.
一方、本発明の一実施例によれば、前記（ａ）段階で、応力の方向は、マグネシウム合金の圧延が形成された方向と平行であり得る。 Meanwhile, according to an embodiment of the present invention, in the step (a), the direction of stress may be parallel to the direction in which the magnesium alloy is rolled.
（ｂ）段階で、（ａ）段階の応力を印加している最中に、前記マグネシウム合金に少なくとも１回のパルス電流を印加することができる。図１に示したように、引張成形用装置の外部電力装置を通じて引張成形用試片１０にパルス電流を印加することができる。図２に示したように、パルス電流は、一定の電流印加周期（ｔｐ）、電流印加時間（ｔｄ）で印加する。パルス電流は、一定の電流密度（ρｉ）で印加されるが、これは、引張成形用試片に引張力が印加されることによって、断面積が変化する時、印加されるパルス電流の強度を調節して、電流密度を一定に保持することができる。 In the step (b), at least one pulse current can be applied to the magnesium alloy while the stress in the step (a) is being applied. As shown in FIG. 1, a pulse current can be applied to the tensile molding specimen 10 through an external power device of the tensile molding apparatus. As shown in FIG. 2, the pulse current is applied at a constant current application period (t p ) and current application time (t d ). The pulse current is applied at a constant current density (ρ i ), which is the intensity of the applied pulse current when the cross-sectional area is changed by applying a tensile force to the tensile molding specimen. To keep the current density constant.
一方、本発明の一実施例によれば、前記パルス電流の電流密度は、少なくとも１００Ａ／ｍｍ２以上であり得る。 Meanwhile, according to an embodiment of the present invention, the current density of the pulse current may be at least 100 A / mm 2 or more.
一方、本発明の一実施例によれば、前記パルス電流の電流印加周期（ｔｐ）は、１８秒〜２２秒であり、電流印加時間（ｔｄ）は、０．４秒〜０．６秒であり得る。 Meanwhile, according to an embodiment of the present invention, the current application period (t p ) of the pulse current is 18 seconds to 22 seconds, and the current application time (t d ) is 0.4 seconds to 0.6 seconds. Could be seconds.
次いで、本明細書の引張成形において意味する用語について説明する。 Next, terms used in the tensile molding of this specification will be described.
延伸率（ｓｔｒａｉｎ）とは、部品や試片の線形寸法の単位長さ当たりの変化率を意味し、公称ひずみ（Ｅｎｇｉｎｅｅｒｉｎｇ ｓｔｒａｉｎ）と真ひずみ（Ｔｒｕｅ ｓｔｒａｉｎ）との２種がある。公称ひずみが普遍的に使われる延伸率であり、初期表点距離に対する長さの変化として下記の式で表現される。 The stretch rate means the rate of change per unit length of the linear dimension of a part or specimen, and there are two types, nominal strain (true strain) and true strain (true strain). Nominal strain is a universally used stretch ratio and is expressed by the following formula as a change in length with respect to the initial table point distance.
σ＝（Ｌ−Ｌ０）／Ｌ
（σ：延伸率、Ｌ：成形後の標点距離、Ｌ０：初期標点距離）
σ = (L−L 0 ) / L
(Σ: Stretch rate, L: Marking distance after molding, L 0 : Initial marking distance)
降伏強度（以下、ＹＳ）とは、塑性変形を発生させず、材料に加えられる最大応力の程度であって、材料が特定の永久変形を示す時の応力を意味する。 Yield strength (hereinafter referred to as YS) means the maximum stress applied to a material without causing plastic deformation and means the stress when the material exhibits a specific permanent deformation.
塑性区間（以下、ＰＲ）とは、弾性限界を超えて降伏強度を過ぎた試片が塑性変形を帯びる区間であり、荷重の原因を除去した後にも、永久的な変形が残っている区間である。 A plastic section (hereinafter referred to as PR) is a section in which a specimen that exceeds the elastic limit and has exceeded the yield strength is plastically deformed, and is a section in which permanent deformation remains even after the cause of the load is removed. is there.
最大引張強度（以下、ＵＴＳ）とは、試片の強度を示す力で試片が破断になるまで引張力を印加した時、耐える最大応力を意味する。応力−ひずみ線図で最大応力地点を意味する。 The maximum tensile strength (hereinafter referred to as UTS) means the maximum stress that can be withstood when a tensile force is applied until the specimen breaks with a force indicating the strength of the specimen. The stress-strain diagram means the maximum stress point.
以下、多様な実験例によって、パルス電流印加によるマグネシウム合金成形性増加方法に及ぼす効果について説明する。 Hereinafter, the effects of the pulse current application on the magnesium alloy formability increasing method will be described with various experimental examples.
＜実施例１．最初のパルス電流印加地点変化による引張特性＞
図３ないし図１０を参照して、パルス電流印加によるマグネシウム合金成形性増加方法に及ぼす効果について説明する。
<Example 1. Tensile properties due to first pulse current application point change>
With reference to FIG. 3 thru | or FIG. 10, the effect which it has on the magnesium alloy formability increasing method by pulse current application is demonstrated.
試片１０は、焼鈍処理していないマグネシウムＡＺ３１素材、例えば、ＡＺ３１−圧延材、ＡＺ３１−焼鈍材、ＡＺ９１などの商用マグネシウム合金であり、全長（ａ）は、１００ｍｍであり、標点距離は、２５ｍｍ、試片の断片長は、６．２５ｍｍであり得る。但し、図３によって、本発明の実施例が限定されるものではない。 Specimen 10 is a magnesium AZ31 material that has not been annealed, for example, commercial magnesium alloys such as AZ31-rolled material, AZ31-annealed material, AZ91, and the total length (a) is 100 mm. The piece length of 25 mm and the specimen can be 6.25 mm. However, the embodiment of the present invention is not limited by FIG.
一般的に、マグネシウム合金を成形するためには、焼鈍処理段階を経た後、引張成形のような工程を通じて所望の形状にマグネシウム合金を成形することができる。しかし、本発明によるマグネシウム合金成形性増加方法は、焼鈍処理していないマグネシウム合金を用いてパルス電流を印加しながら、引張成形を行っても、さらに高い延伸率を有することができるために、焼鈍処理の段階を省略することができる効果がある。 In general, in order to form a magnesium alloy, the magnesium alloy can be formed into a desired shape through a process such as tensile forming after passing through an annealing step. However, the method for increasing the formability of a magnesium alloy according to the present invention has a higher drawing ratio even when a tensile current is applied while applying a pulse current using a magnesium alloy that has not been annealed. There is an effect that the processing stage can be omitted.
図４は、本発明の比較例による引張成形時の応力−ひずみ線図を示すグラフである。 FIG. 4 is a graph showing a stress-strain diagram during tensile molding according to a comparative example of the present invention.
まず、本発明によるパルス電流印加引張成形の比較例について説明する。 First, a comparative example of pulse current application tension molding according to the present invention will be described.
［比較例１］
比較例１は、図３に示した引張成形用試片を図１のパルス電流印加引張成形用装置にローディングし、パルス電流を印加せず、引張力を印加して引張成形を実行する。比較例１の引張力の引張方向は、前記マグネシウム合金試片の圧延方向（ＲＤ）、マグネシウム合金の引張変形速度は、０．０２５ｍｍ／ｓであり得る。
[Comparative Example 1]
In Comparative Example 1, the tensile molding specimen shown in FIG. 3 is loaded on the pulse current application tension molding apparatus shown in FIG. 1, and the tension molding is executed without applying the pulse current and applying the tensile force. The tensile direction of the tensile force of Comparative Example 1 may be the rolling direction (RD) of the magnesium alloy specimen, and the tensile deformation rate of the magnesium alloy may be 0.025 mm / s.
前記実験によって、比較例１の引張成形を実行した結果、降伏強度と最大引張強度は、それぞれ２６０Ｍｐａと３００Ｍｐａであり、延伸率は、０．１５に測定された。 As a result of performing the tensile molding of Comparative Example 1 according to the experiment, the yield strength and the maximum tensile strength were 260 Mpa and 300 Mpa, respectively, and the stretch ratio was measured to 0.15.
［比較例２］
比較例２は、マグネシウム合金をＡＺ３１−焼鈍材を使用して比較例１のような方法で引張成形を実行する。マグネシウム合金ＡＺ３１−焼鈍材素材は、マグネシウムＡＺ３１−圧延材を焼鈍処理したものであって、一般的なマグネシウム合金のうち、軟性が高くて、工業用材料として使われる素材である。前記実験の結果、比較例２によるＡＺ３１−焼鈍材素材は、延伸率が０．２２に測定された。
[Comparative Example 2]
In comparative example 2, a magnesium alloy is subjected to tensile molding by the method as in comparative example 1 using AZ31-annealed material. The magnesium alloy AZ31-annealed material is a material obtained by annealing magnesium AZ31-rolled material, and is a material used as an industrial material because of its high flexibility among general magnesium alloys. As a result of the experiment, the stretching ratio of the AZ31-annealed material according to Comparative Example 2 was measured to be 0.22.
次いで、本発明の実施例であるパルス電流印加引張成形について説明する。 Next, a description will be given of the pulse current application tension forming which is an embodiment of the present invention.
図５は、本発明の一実施例及び比較例によるパルス電流を印加して、引張成形時のパルス電流印加引張成形用試片の破断形状を示す写真である。図６は、本発明の一実施例によるパルス電流を印加して、引張成形時の応力−ひずみ線図を示すグラフであり、図７は、本発明の一実施例によるパルス電流を印加して、引張成形時の温度変化を示すグラフである。 FIG. 5 is a photograph showing a fractured shape of a tensile test specimen for applying pulse current by applying a pulse current according to one embodiment of the present invention and a comparative example. FIG. 6 is a graph showing a stress-strain diagram at the time of tensile forming by applying a pulse current according to an embodiment of the present invention, and FIG. 7 is a graph showing applying a pulse current according to an embodiment of the present invention. It is a graph which shows the temperature change at the time of tension molding.
本実施例において、パルス電流印加引張成形時に、試片形状の変形速度は、０．０２５ｍｍ／ｓであって、比較例と同様に引張成形を行い、パルス電流は、電流密度（ρ）は１００Ａ／ｍｍ２、電流印加時間（ｔｄ）は０．５秒、電流印加周期（ｔｐ）は２０秒に設定して実験した。また、試片の電流印加時点は、マグネシウム合金試片の塑性変形以後、最初のパルス電流が印加され、３回の試験は、それぞれ最初のパルス電流をマグネシウム合金試片の降伏強度（ＹＳ）地点、塑性区間（ＰＲ）または最大引張強度（ＵＴＳ）地点で印加した。この際、試片に印加される電流密度（ρｉ）を一定にして、温度変化を最小化するために、試片の断面積の減少を考慮した電流値を印加して、電流密度を一定に保持させる。 In this example, at the time of pulse current application tensile molding, the deformation rate of the specimen shape is 0.025 mm / s, and tensile molding is performed in the same manner as in the comparative example. The pulse current has a current density (ρ) of 100 A. / Mm 2 , the current application time (t d ) was set to 0.5 seconds, and the current application period (t p ) was set to 20 seconds. In addition, the first pulse current is applied after the plastic deformation of the magnesium alloy specimen when the specimen current is applied. In the three tests, the first pulse current is used as the yield strength (YS) point of the magnesium alloy specimen. Applied at the plastic section (PR) or maximum tensile strength (UTS) point. At this time, in order to keep the current density (ρ i ) applied to the specimen constant and minimize the change in temperature, the current density is kept constant by applying a current value in consideration of the decrease in the cross-sectional area of the specimen. To hold.
本発明の一実施例によれば、前記（ｂ）段階で、前記パルス電流の最初のパルス電流をマグネシウム合金の降伏強度地点、塑性区間または最大引張強度地点で印加することができる。 According to an embodiment of the present invention, in the step (b), the first pulse current of the pulse current can be applied at a yield strength point, a plastic interval or a maximum tensile strength point of the magnesium alloy.
前記実験の結果、パルス電流を印加しながら、引張成形を行う時、電流を印加する時間、パルス周期、電流密度によって、応力−ひずみ線図で応力特性と延伸率特性とが異ならせて表われ、温度の増加量が変わりうる。 As a result of the experiment, when performing tensile forming while applying a pulse current, the stress characteristics and the stretch ratio characteristics are different in the stress-strain diagram depending on the time of applying the current, the pulse period, and the current density. The amount of temperature increase can vary.
最初のパルス電流印加地点が、降伏強度（ＹＳ、２００ＭＰａ）地点である時、延伸率が０．３３にパルス電流を印加していない比較例１（延伸率＝０．１５）に比べて、延伸率が１２０％向上した。最初のパルス電流印加地点が、塑性区間（ＰＲ、２８０ＭＰａ）である時、延伸率は０．３６であって、比較例１に比べて、１４０％延伸率が向上し、降伏強度地点で最初のパルス電流を印加した時よりもさらに向上した延伸率を示した。 When the first pulse current application point is the yield strength (YS, 200 MPa) point, the drawing rate is 0.33, compared with Comparative Example 1 (drawing rate = 0.15) in which no pulse current is applied. The rate increased by 120%. When the first pulse current application point is a plastic section (PR, 280 MPa), the stretch ratio is 0.36, which is 140% higher than that of Comparative Example 1, and the first yield current point at the yield strength point. The stretch ratio was further improved as compared to when a pulse current was applied.
また、最初のパルス電流印加地点が、最大引張強度（ＵＴＳ、３００ＭＰａ）地点である時、延伸率は０．４１であって、最大延伸率を示し、比較例１に比べて、１７０％延伸率が向上した。これは、ある程度変形が進行した時、パルス電流を印加することがさらに多い再結晶の駆動力を有しているために、延伸率の側面でさらに高い向上率を示したと予測される。 In addition, when the first pulse current application point is the point of maximum tensile strength (UTS, 300 MPa), the stretching ratio is 0.41 and shows the maximum stretching ratio. Compared with Comparative Example 1, the stretching ratio is 170%. Improved. This is presumed that when the deformation progresses to some extent, it has a driving force for recrystallization that is more often applied with a pulse current, and therefore has a higher improvement rate in terms of stretch ratio.
一方、図７に示したように、前記実験による温度測定の結果（熱電対によって測定される）と校正されたＦＬＩＲ熱画像カメラを用いて素材のパルス電流印加引張成形のうち、電流印加による試片の最大平均温度を測定した結果、前記３回の実験条件いずれも４００℃でほぼ同様に測定された。これは、温度影響を排除するために、パルス電流印加時に、試片の減少する断面積を考慮して電流値を変化させて、電流密度を同様に保持したためである。 On the other hand, as shown in FIG. 7, the results of temperature measurement by the above experiment (measured by a thermocouple) and the pulsated FLIR thermal image camera using a calibrated FLIR thermal imaging camera were tested by applying current. As a result of measuring the maximum average temperature of the pieces, all of the three experimental conditions were measured in the same manner at 400 ° C. This is because, in order to eliminate the influence of temperature, the current value was similarly maintained by changing the current value in consideration of the cross-sectional area where the specimen decreases, when applying the pulse current.
マグネシウム合金を成形するためには、焼鈍処理段階を経た後、引張成形のような工程を通じて所望の形状にマグネシウム合金を成形することができる。しかし、本発明によるマグネシウム合金成形性増加方法は、焼鈍処理していないマグネシウム合金を用いてパルス電流を印加しながら、引張成形を行っても、さらに高い延伸率を有することができるために、焼鈍処理の段階を省略することができる効果がある。すなわち、マグネシウム合金の成形性を増加させる効果がある。 In order to form the magnesium alloy, the magnesium alloy can be formed into a desired shape through a process such as tensile forming after passing through the annealing treatment stage. However, the method for increasing the formability of a magnesium alloy according to the present invention has a higher drawing ratio even when a tensile current is applied while applying a pulse current using a magnesium alloy that has not been annealed. There is an effect that the processing stage can be omitted. That is, there is an effect of increasing the formability of the magnesium alloy.
＜実施例２．３回のパルス電流印加条件の引張特性＞
図８ないし図１０を参照して、パルス電流を３回印加した時、マグネシウム合金試片の引張特性について説明する。
<Example 2. Tensile characteristics under three pulse current application conditions>
With reference to FIGS. 8 to 10, the tensile properties of the magnesium alloy specimen when the pulse current is applied three times will be described.
図８は、本発明の一実施例による３回のパルス電流を印加して、引張成形時のパルス電流印加引張成形用試片の破断形状を示す写真であり、図９は、本発明の一実施例による３回のパルス電流を印加して、引張成形時の応力−ひずみ線図及び温度変化を示すグラフである。 FIG. 8 is a photograph showing a fracture shape of a tensile test specimen for applying pulse current at the time of tensile molding by applying three pulse currents according to an embodiment of the present invention, and FIG. It is a graph which shows the stress-strain diagram at the time of tension forming, and a temperature change by applying the pulse current 3 times by an Example.
前記実施例１と同じ引張成形速度、電流密度、電流印加時間、電流印加周期の条件下に、降伏強度地点、塑性区間、最大引張強度地点で３回のパルスのみを印加して引張成形を実行した。少ないパルス印加に比べて、物性向上率が高いほど、実工程に適用可能性が増加するので、３回のパルスのみ印加した。 Tensile forming is performed by applying only three pulses at the yield strength point, the plastic section, and the maximum tensile strength point under the same conditions as in Example 1 above, ie, the tensile forming speed, current density, current application time, and current application cycle. did. Compared with the application of a small number of pulses, the higher the property improvement rate, the higher the applicability to the actual process, so only three pulses were applied.
図９を参照すれば、前記実験の結果、３回のパルス電流のみを印加しても、高い延伸率を示すことを確認することができる。 Referring to FIG. 9, as a result of the experiment, it can be confirmed that even when only three pulse currents are applied, a high stretch ratio is exhibited.
本発明の一実施例によれば、マグネシウム合金は、延伸率が０．１８〜０．４１であり得る。 According to an embodiment of the present invention, the magnesium alloy may have a draw ratio of 0.18 to 0.41.
降伏強度地点と塑性区間で最初のパルス電流を印加した条件に対してパルス電流印加回数を３回にした時、延伸率は、それぞれ０．１８、０．１９に測定され、これは、一般引張条件（延伸率＝０．１５）に比べて、２６％程度の延伸率の向上を示す。これに比べて、最初のパルス電流印加地点が最大引張強度地点である場合、延伸率は、０．２７であって、一般引張条件に比べて、８０％の延伸率の向上率を示すだけではなく、延伸率が０．２２である既存のマグネシウム合金ＡＺ３１−焼鈍材素材よりも遥かに向上した延伸率を示す。 When the number of applied pulse currents was set to 3 for the conditions in which the first pulse current was applied at the yield strength point and the plastic section, the stretching ratios were measured to be 0.18 and 0.19, respectively. Compared to the conditions (stretch ratio = 0.15), the stretch ratio is improved by about 26%. Compared to this, when the first pulse current application point is the maximum tensile strength point, the stretching ratio is 0.27, and it is only necessary to show an improvement ratio of 80% stretching ratio compared with the general tensile conditions. The drawing ratio is much higher than that of the existing magnesium alloy AZ31-annealed material having a drawing ratio of 0.22.
前記実験の結果、パルス電流印加引張成形技術を利用すれば、既存の温間成形時に必要であった熱処理段階を省略することができる効果がある。また、各条件での強度を見れば、変形後半部にパルス電流を印加するほど、流動応力が減少したことが分かり、最大引張強度も、最も後半部にパルス電流印加時に最も低い値である２３５ＭＰａで表われて、同じ電流条件に対しても、パルス印加地点によって再結晶の程度、すなわち、微細組織が変わることを確認することができる。 As a result of the experiment, if the pulse current application tension forming technique is used, there is an effect that the heat treatment step required in the existing warm forming can be omitted. In addition, the strength under each condition shows that the flow stress decreases as the pulse current is applied to the second half of the deformation, and the maximum tensile strength is 235 MPa, which is the lowest value when the pulse current is applied to the second half. It can be confirmed that the degree of recrystallization, that is, the microstructure changes depending on the pulse application point even under the same current condition.
一方、ＦＬＩＲ熱画像カメラを用いて試片の全体平均温度を測定した結果、最初のパルス電流印加地点が、降伏強度、塑性区間、最大引張強度条件に対していずれも３００℃〜３５０℃の間で測定されて、電流密度がある程度同様に保持されたと考えられるが、後半部に電流印加時に、温度の上昇幅が少し増加したことを確認することができる。 On the other hand, as a result of measuring the overall average temperature of the specimen using the FLIR thermal imaging camera, the first pulse current application point was between 300 ° C. and 350 ° C. with respect to the yield strength, plastic section, and maximum tensile strength conditions. It is considered that the current density was maintained in a similar manner to some extent, but it can be confirmed that the temperature increase slightly increased when the current was applied to the latter half.
＜微細組織及び集合組織の分析（ＥＢＳＤ分析）＞
図１０ないし図１４を参照して、パルス電流印加引張成形後のマグネシウム合金試片の微細組織及び集合組織の分析について説明する。
<Analysis of microstructure and texture (EBSD analysis)>
The analysis of the microstructure and texture of the magnesium alloy specimen after pulse current application tensile forming will be described with reference to FIGS.
図１０は、本発明の一実施例及び比較例による初期試片及びパルス電流印加引張成形後、試片の微細組織及び集合組織を示す光学顕微鏡写真であり、図１１ないし図１４は、本発明の一実施例によるパルス電流印加引張成形後、試片の微細組織及び集合組織を示すＥＢＳＤ分析写真及びＫＡＭ分析写真である。 FIG. 10 is an optical micrograph showing the microstructure and texture of the specimen after tensile molding with an initial specimen and pulse current applied according to one example and comparative example of the present invention. FIGS. 11 to 14 show the present invention. 2 is an EBSD analysis photograph and a KAM analysis photograph showing the microstructure and texture of a specimen after pulse forming with pulse current application according to an embodiment of the present invention.
まず、図１０を参照して、パルス電流印加引張成形を行う前、マグネシウム合金ＡＺ３１−圧延材素材の初期微細組織及び集合組織の分析について説明する。 First, the analysis of the initial microstructure and texture of the magnesium alloy AZ31-rolled material before the pulse current application tensile forming will be described with reference to FIG.
図１０の（ａ）は、ＡＺ３１−圧延材素材の初期微細組織及び集合組織を示す光学顕微鏡写真である。初期試片の内部に存在するｔｗｉｎ分布、結晶粒サイズ、結晶粒形態などを確認することができる。ＡＺ３１−圧延材素材に対するＮＤ方向に垂直な面の初期微細組織の観察結果、数マイクロサイズの結晶粒と多量のｔｗｉｎとが観察される。また、圧延処理になった初期組織であることにもかかわらず、一部の再結晶がなされた結晶粒が存在すると確認され、前記試片の場合、温間で圧延処理がなされたものと見られる。 FIG. 10A is an optical micrograph showing the initial microstructure and texture of the AZ31-rolled material. The twin distribution, crystal grain size, crystal grain morphology, etc. existing in the initial specimen can be confirmed. As a result of observing the initial microstructure of the plane perpendicular to the ND direction with respect to the AZ31-rolled material, several micro-sized crystal grains and a large amount of twin are observed. In addition, it was confirmed that some recrystallized grains existed in spite of being the initial structure subjected to the rolling process. In the case of the specimen, it was considered that the rolling process was performed warmly. It is done.
次いで、マグネシウム合金ＡＺ３１−圧延材素材の引張成形以後の微細組織の分析について説明する。図１０の（ｂ）ないし図１０の（ｅ）を参照すれば、ＡＺ３１−圧延材素材の引張成形以後、微細組織の変化を示す光学顕微鏡写真である。塑性変形がある程度進行したそれぞれの試片に対して、パルス電流印加有無によるマグネシウム合金の微細組織の変化を示す。 Next, analysis of the microstructure after the tensile forming of the magnesium alloy AZ31-rolled material will be described. Referring to FIGS. 10 (b) to 10 (e), these are optical micrographs showing changes in the microstructure after tensile forming of the AZ31-rolled material. For each specimen where plastic deformation has progressed to some extent, the change in the microstructure of the magnesium alloy with and without pulse current application is shown.
図１０の（ｂ）と図１０の（ｃ）は、それぞれ塑性変形が６％である時、パルス電流を印加せず、一般引張成形を実行したマグネシウム合金と、パルス電流を印加して引張成形を実行したマグネシウム合金と、の微細組織を示す光学顕微鏡写真である。図１０の（ｃ）の場合、パルス電流は、５回印加された。 10 (b) and 10 (c), respectively, when the plastic deformation is 6%, a pulse current is not applied, a magnesium alloy that has been subjected to general tensile forming, and a tensile current is applied by applying a pulse current. It is the optical microscope photograph which shows the fine structure of the magnesium alloy which performed this. In the case of FIG. 10C, the pulse current was applied five times.
図１０の（ｄ）と図１０の（ｅ）は、それぞれ塑性変形が１６％である時、パルス電流を印加せず、一般引張成形を実行したマグネシウム合金と、パルス電流を印加して引張成形を実行したマグネシウム合金と、の微細組織を示す光学顕微鏡写真である。図１０の（ｅ）の場合、パルス電流は、１１回印加された。 10 (d) and 10 (e) show a magnesium alloy that has been subjected to general tensile forming without applying a pulse current when the plastic deformation is 16%, and a tensile forming by applying a pulse current. It is the optical microscope photograph which shows the fine structure of the magnesium alloy which performed this. In the case of FIG. 10E, the pulse current was applied 11 times.
マグネシウム合金試片微細組織の光学顕微鏡分析結果、一般塑性変形が進行する時は、結晶粒の形状やサイズが初期組織に比べて、大きな差が観察されなかったが、同じ変形率である時、一般引張成形時よりもパルス電流が印加された試片で結晶粒サイズがさらに大きく観察され、ほとんどの結晶の再結晶が起こったことが観察された。 As a result of optical microscopic analysis of the microstructure of the magnesium alloy specimen, when the general plastic deformation progresses, no significant difference was observed in the shape and size of the crystal grains compared to the initial structure, but when the deformation rate is the same, The crystal grain size was observed to be larger in the specimen to which the pulse current was applied than in the general tensile molding, and it was observed that most of the crystals were recrystallized.
次いで、図１１及び図１２を参照して、実施例１によるパルス電流印加引張成形によるマグネシウム合金ＡＺ３１−圧延材素材のＥＢＳＤ及びＫＡＭ分析を利用した微細組織及び集合組織の変化態様について説明する。 Next, with reference to FIG. 11 and FIG. 12, changes in the microstructure and texture using the EBSD and KAM analysis of the magnesium alloy AZ31-rolled material material by pulse current application tension forming according to Example 1 will be described.
図１１は、本発明の一実施例による初期試片及びパルス電流印加引張成形後、試片の微細組織及び集合組織を示すＥＢＳＤ分析写真である。 FIG. 11 is an EBSD analysis photograph showing the microstructure and texture of the specimen after the initial specimen and pulse current application tension molding according to an embodiment of the present invention.
図１１の（ａ）は、ＡＺ３１−圧延材素材の初期試片のＮＤ方向のＥＢＳＤ微細組織の分析を示す写真である（ここで、ＮＤ（ｎｏｒｍａｌ ｄｉｒｅｃｔｉｏｎ）方向は、圧延された試片の圧延面の法線方向を意味する）。光学顕微鏡で確認したように、典型的な圧延材とは異ならせて、一部の再結晶がなされているような結晶粒が観察された。平均結晶粒サイズは、３．４４μｍであると観察された（ｃｒｉｔｉｃａｌ ｍｉｓｏｒｉｅｎｔａｔｉｏｎ ａｎｇｌｅ＞１０°基準）。 FIG. 11 (a) is a photograph showing an analysis of the EBSD microstructure in the ND direction of the initial specimen of AZ31-rolled material (where ND (normal direction) is the rolling of the rolled specimen). Meaning normal direction of the surface). As confirmed by an optical microscope, crystal grains that were partially recrystallized were observed, unlike a typical rolled material. The average grain size was observed to be 3.44 μm (critical misting angle> 10 ° reference).
図１１の（ｂ）は、パルス電流を印加せず、引張成形を行った時、変形率が６％まで進行したＡＺ３１−圧延材素材試片のＥＢＳＤ分析写真であり、図１１の（ｃ）は、パルス電流を降伏強度地点から同時に印加して引張成形を行った時、変形率が６％まで進行したＡＺ３１−圧延材素材試片のＥＢＳＤ分析写真である。図１１の（ｃ）は、パルス電流が５回印加された状態である。 (B) of FIG. 11 is an EBSD analysis photograph of the AZ31-rolled material specimen in which the deformation rate has progressed to 6% when a pulse current is not applied and tensile forming is performed, and (c) of FIG. These are the EBSD analysis photographs of the AZ31-rolled material specimen in which the deformation rate has progressed to 6% when a pulse current is simultaneously applied from the yield strength point and tensile forming is performed. FIG. 11C shows a state where the pulse current is applied five times.
前記分析結果、図１１の（ｂ）及び図１１の（ｃ）の平均結晶粒サイズは、それぞれ３．６２μｍ、７．１５μｍであると観察された（ｃｒｉｔｉｃａｌ ｍｉｓｏｒｉｅｎｔａｔｉｏｎ ａｎｇｌｅ＞１０°基準）。一般引張成形を実行した試片では、初期状態とほぼ類似している状態の平均結晶粒が確認された。一方、パルス電流が印加された試片では、同一変形率の条件である時、一般引張成形を実行した試片に比べて、平均結晶粒サイズが大きくなったことを確認した。パルス電流が印加される時、ほとんどの結晶粒が再結晶されて、均一な等軸晶の形状を有したと見られる。 As a result of the analysis, the average crystal grain sizes in FIGS. 11 (b) and 11 (c) were observed to be 3.62 μm and 7.15 μm, respectively (critical misting angle> 10 ° standard). In the specimen subjected to general tensile forming, average crystal grains in a state almost similar to the initial state were confirmed. On the other hand, it was confirmed that the average crystal grain size of the test piece to which the pulse current was applied was larger than that of the test piece subjected to general tensile forming when the deformation rate was the same. When a pulse current is applied, most of the crystal grains are recrystallized and appear to have a uniform equiaxed crystal shape.
図１２は、本発明の一実施例による初期試片及びパルス電流印加引張成形後、試片の微細組織及び集合組織を示すＫＡＭ分析写真である。ＫＡＭ分析を通じて結晶粒が再結晶されたことを定量的に確認することができる。図１２の（ａ）、図１２の（ｂ）及び図１２の（ｃ）は、それぞれ初期試片、一般引張成形を実行した試片、パルス電流印加引張成形を変形率６％まで実行した試片の微細組織を示す写真である。平均ＫＡＭ ｖａｌｕｅは、それぞれ０．８３９、０．９９、０．７１であって、パルス電流印加成形の場合、一般引張成形に比べて、ＫＡＭ ｖａｌｕｅが０．２８程度減少して、再結晶程度が非常に大きなことを確認することができる。 FIG. 12 is a KAM analysis photograph showing the microstructure and texture of the specimen after the initial specimen and pulse current application tension molding according to one embodiment of the present invention. It can be quantitatively confirmed that the crystal grains are recrystallized through KAM analysis. 12 (a), 12 (b) and 12 (c) respectively show an initial specimen, a specimen that has been subjected to general tensile molding, and a specimen that has been subjected to pulse current application tension molding up to a deformation rate of 6%. It is a photograph which shows the microstructure of a piece. The average KAM values are 0.839, 0.99, and 0.71, respectively. In the case of pulse current application molding, the KAM value is reduced by about 0.28 compared to general tensile molding, and the degree of recrystallization is reduced. It can be confirmed that it is very big.
次いで、図１３及び図１４を参照して、実施例２による３回のパルス電流を印加して引張成形した時、変化するマグネシウム合金ＡＺ３１−圧延材素材のＥＢＳＤ及びＫＡＭ分析を利用した微細組織及び集合組織の変化態様について説明する。 Next, referring to FIG. 13 and FIG. 14, the microstructure using the EBSD and KAM analysis of the magnesium alloy AZ31-rolled material that changes when tensile forming is performed by applying three pulse currents according to Example 2. A change mode of the texture will be described.
まず、図１３は、本発明の一実施例による初期試片及び３回のパルス電流印加引張成形後、試片の微細組織及び集合組織を示すＥＢＳＤ分析写真である。 First, FIG. 13 is an EBSD analysis photograph showing the microstructure and texture of a specimen after an initial specimen according to an embodiment of the present invention and three times of pulse current application tension molding.
図１３の（ａ）は、ＡＺ３１−圧延材素材の初期試片のＮＤ方向のＥＢＳＤ微細組織の分析を示す写真であり、図１３の（ｂ）、図１３の（ｃ）及び図１３の（ｄ）は、ＡＺ３１−圧延材素材のパルス電流をそれぞれ降伏強度（ＹＳ）地点、塑性区間（ＰＲ）、最大引張強度（ＵＴＳ）地点で３回のパルス電流を印加して引張成形を行った後のＥＢＳＤ分析の結果を示す写真である。 (A) of FIG. 13 is a photograph showing an analysis of the EBSD microstructure in the ND direction of the initial specimen of AZ31-rolled material, and (b), (c) and (c) of FIG. d) After forming the pulse current of AZ31-rolled material material by applying three pulse currents at the yield strength (YS) point, the plastic section (PR), and the maximum tensile strength (UTS) point, respectively. It is a photograph which shows the result of EBSD analysis of.
分析結果、図１３の（ａ）ないし図１３の（ｄ）の平均結晶粒サイズは、それぞれ３．４４μｍ、６．８５μｍ、７．３μｍ、８．５８μｍに測定された。同一電流密度条件で変形後半部に行くほど、遥かに大きな結晶粒が確認され、これは、変形後半部であるほど、再結晶が起こりうる駆動力が大きくなるために、最大引張強度地点でパルス電流を印加した試片の平均結晶粒サイズ及び再結晶程度が最も大きいと確認される。図１３の（ｅ）は、前記実験の結果によるマグネシウム合金試片の平均結晶粒サイズを示すグラフである。 As a result of the analysis, the average crystal grain sizes of FIGS. 13A to 13D were measured to be 3.44 μm, 6.85 μm, 7.3 μm, and 8.58 μm, respectively. The farther the deformation is in the second half of the deformation under the same current density condition, the larger the crystal grain is confirmed. This is because the driving force that can cause recrystallization increases in the second half of the deformation. It is confirmed that the average grain size and recrystallization degree of the specimen to which current was applied were the largest. FIG. 13E is a graph showing the average crystal grain size of the magnesium alloy specimen obtained as a result of the experiment.
図１４は、本発明の一実施例による初期試片及び３回のパルス電流印加引張成形後、試片の微細組織及び集合組織を示すＫＡＭ分析写真である。 FIG. 14 is a KAM analysis photograph showing the microstructure and texture of the specimen after the initial specimen and three pulse current application tension moldings according to an embodiment of the present invention.
基本的に、平均ＫＡＭ ｖａｌｕｅは、変形によって大きくなる。しかし、前記分析結果、同一電流密度の条件下に変形後半部に行くほど、平均ＫＡＭ ｖａｌｕｅは減少し、これは、再結晶がさらに多くなされたことによる結果である。図１４の（ａ）、図１４の（ｂ）、図１４の（ｃ）及び図１４の（ｄ）の平均ＫＡＭ ｖａｌｕｅは、それぞれ０．６９、０．６６、０．５９、０．４８３に測定された。これを通じて、変形後半部であるほど、再結晶が起こりうる駆動力が大きくなって、最初パルスが印加された時点が最も後半部である最大引張強度地点である時、再結晶程度が最も大きなことを定量的に確認することができる。 Basically, the average KAM value increases with deformation. However, as a result of the analysis, the average KAM value decreases as the deformation proceeds to the second half under the condition of the same current density, which is a result of further recrystallization. The average KAM values in FIGS. 14 (a), 14 (b), 14 (c) and 14 (d) are 0.69, 0.66, 0.59 and 0.483, respectively. Measured. Through this, the driving force at which recrystallization can occur increases in the second half of the deformation, and when the first pulse is applied to the maximum tensile strength point, which is the second half, the recrystallization degree is the largest. Can be confirmed quantitatively.
したがって、本発明によるマグネシウム合金引張成形中にパルス電流を印加すれば、マグネシウム合金試片の再結晶程度が大きくなり、延伸率が向上して成形性を増加させることができる。 Therefore, if a pulse current is applied during the magnesium alloy tensile molding according to the present invention, the degree of recrystallization of the magnesium alloy specimen is increased, and the stretch ratio is improved and the formability can be increased.
＜通電熱処理の実験＞
図１５及び図１６を参照して、パルス電流を印加した時、マグネシウム合金の再結晶速度に及ぼす影響について説明する。
<Electric heat treatment experiment>
With reference to FIG.15 and FIG.16, the influence which it has on the recrystallization speed | rate of a magnesium alloy when a pulse current is applied is demonstrated.
図１５は、本発明の一実施例による引張成形時に、温度または時間による試片の再結晶分率を示すグラフであり、図１６は、本発明の一実施例による引張成形時に、パルス電流印加条件と、熱処理条件と、で再結晶が５０％起こった地点に対する時間−温度グラフである。 FIG. 15 is a graph showing the recrystallization fraction of a specimen according to temperature or time during tension forming according to an embodiment of the present invention, and FIG. 16 is a pulse current application during tension forming according to an embodiment of the present invention. It is a time-temperature graph with respect to the point where 50% of recrystallization occurred under the conditions and heat treatment conditions.
本発明の一実施例によれば、パルス電流を印加すれば、マグネシウム合金で再結晶速度が増加する。 According to one embodiment of the present invention, when a pulse current is applied, the recrystallization rate is increased in the magnesium alloy.
図１５の（ａ）は、温度による再結晶速度（分率）を示すグラフであり、図１５の（ｂ）は、経時的な再結晶速度（分率）を示すグラフである。前記図面で、Ｘｒ（Ｃｏｎｖｅｒｓｉｏｎ ｏｆ ｒｅｃｒｙｓｔａｌｌｉｚａｔｉｏｎ）は、再結晶分率を意味する。 FIG. 15A is a graph showing the recrystallization rate (fraction) according to temperature, and FIG. 15B is a graph showing the recrystallization rate (fraction) over time. In the drawings, X r (Conversion of recrystallization) means a recrystallization fraction.
まず、５０％まで圧延したＡＺ３１−圧延材素材に対してパルス電流印加処理と熱処理とを行った後に、ＥＢＳＤのＧＯＳ（Ｇｒａｉｎ Ｏｒｉｅｎｔａｔｉｏｎ Ｓｐｒｅａｄ）を通じて再結晶程度を分析した。 First, a pulse current application process and a heat treatment were performed on the AZ31-rolled material material rolled to 50%, and then the recrystallization degree was analyzed through EBSD GOS (Grain Orientation Spread).
図１５の（ａ）を参照すれば、保持時間を３０分に一定にして、温度による再結晶分率を分析した結果、パルス電流印加処理された試片は、１７５℃から再結晶が起こり始め、２５０℃に再結晶が完全に完了したことが確認された。一方、熱処理された試片は、２００℃に再結晶が起こり始め、３５０℃に再結晶が完全に完了したことが確認された。 Referring to FIG. 15 (a), as a result of analyzing the recrystallization fraction depending on the temperature while keeping the holding time constant at 30 minutes, the specimen subjected to the pulse current application process starts to recrystallize at 175 ° C. It was confirmed that the recrystallization was completely completed at 250 ° C. On the other hand, the heat-treated specimen started to recrystallize at 200 ° C., and it was confirmed that the recrystallization was completely completed at 350 ° C.
また、図１５の（ｂ）を参照すれば、保持温度を２５０℃に一定にして、経時的な再結晶分率を分析した結果、パルス電流印加処理された試片は、３０分が経過した時、完全に再結晶が完了したことが確認され、熱処理された試片は、１１２時間が経過した時、完全に再結晶が完了したことが確認された。したがって、パルス電流を印加して処理する場合、熱処理条件で比較した時、低い温度と早い時間とに再結晶が完了することを確認して、パルス電流がマグネシウム金属の再結晶を加速化させることを確認することができる。 Referring to (b) of FIG. 15, the retention temperature was kept constant at 250 ° C., and the recrystallization fraction over time was analyzed. As a result, 30 minutes passed for the specimen subjected to the pulse current application treatment. At that time, it was confirmed that the recrystallization was completely completed, and it was confirmed that the heat-treated specimen was completely recrystallized after 112 hours. Therefore, when processing by applying pulse current, when compared under heat treatment conditions, confirm that recrystallization is completed at low temperature and early time, and pulse current can accelerate recrystallization of magnesium metal Can be confirmed.
図１６は、本発明の一実施例による引張成形時に、パルス電流印加条件と、熱処理条件と、で再結晶が５０％起こった地点に対する時間−温度グラフである。図１６で、ｔ５０は、再結晶分率が５０％になるまでかかった時間を意味する。 FIG. 16 is a time-temperature graph for a point at which 50% recrystallization occurs under pulse current application conditions and heat treatment conditions during tensile forming according to an embodiment of the present invention. In FIG. 16, t 50 means the time taken for the recrystallization fraction to reach 50%.
再結晶速度に電流が及ぼす影響を定量化するために、下記のアレニウスの式（Ａｒｒｈｅｎｉｕｓ ｅｑｕａｔｉｏｎ）を用いて再結晶に必要な活性化エネルギーを計算した。パルス電流印加処理条件と熱処理条件とで温度によってマグネシウム合金試片の再結晶が５０％完了する時間を測定した。それを用いて１／時間、１／温度ｓｃａｌｅでプロット（ｐｌｏｔ）して、傾きを通じて再結晶活性化エネルギーを計算した。 In order to quantify the effect of current on the recrystallization rate, the activation energy required for recrystallization was calculated using the following Arrhenius equation. The time required for 50% recrystallization of the magnesium alloy specimen was measured according to the temperature under the pulse current application treatment condition and the heat treatment condition. Using this, the recrystallization activation energy was calculated through the slope by plotting with 1 / hour, 1 / temperature scale.
ｋ１＝ｋ０ｅｘｐ（−Ｅａ／ＲＴ）
（ｋ：速度定数、Ｅａ：活性化エネルギー、Ｔ：絶対温度、Ｒ：気体定数（８．３１４Ｊ／ｍｏｌ Ｋ））
k 1 = k 0 exp (−E a / RT)
(K: rate constant, Ea: activation energy, T: absolute temperature, R: gas constant (8.314 J / mol K))
図１６のグラフの傾きを通じて再結晶活性化エネルギーを導出した結果、熱処理条件では、再結晶活性化エネルギー値が１３７．４ＫＪ／ｍｏｌであり、パルス電流印加条件では、５６．５ＫＪ／ｍｏｌである。したがって、パルス電流印加処理条件でマグネシウム合金試片の再結晶活性化エネルギーがさらに低い値を有し、パルス電流によって再結晶の駆動力が促進されて、再結晶速度が増加することを確認することができる。 As a result of deriving the recrystallization activation energy through the slope of the graph of FIG. 16, the recrystallization activation energy value is 137.4 KJ / mol under the heat treatment condition, and 56.5 KJ / mol under the pulse current application condition. Therefore, confirm that the recrystallization activation energy of the magnesium alloy specimen has a lower value under the pulse current application treatment condition, and that the driving force of recrystallization is promoted by the pulse current and the recrystallization speed increases. Can do.
本発明は、前述したように望ましい実施例を挙げて図示して説明したが、前記実施例に限定されず、本発明の精神を外れない範囲内で当業者によって多様な変形と変更とが可能である。そのような変形例及び変更例は、本発明と添付の特許請求の範囲の範囲内に属するものと認めなければならない。 Although the present invention has been illustrated and described with reference to the preferred embodiments as described above, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made by those skilled in the art without departing from the spirit of the present invention. It is. Such variations and modifications should be recognized as falling within the scope of the present invention and the appended claims.
Claims (12)
（ｂ）前記応力を印加している最中に、前記マグネシウム合金に少なくとも１回のパルス電流を印加する段階と、
を含むマグネシウム合金の成形性増加方法。 (A) applying a stress to the magnesium alloy;
(B) applying at least one pulse current to the magnesium alloy during the application of the stress;
Method for increasing formability of magnesium alloy containing
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| CN110512159A (en) * | 2019-10-08 | 2019-11-29 | 吉林大学 | It is a kind of for eliminating the pulsed current annealing device and its control method of processing hardening in magnesium alloy |
| CN111549305A (en) * | 2020-05-18 | 2020-08-18 | 中南大学 | Strengthening and toughening method for magnesium alloy strip |
| CN112760577A (en) * | 2020-12-28 | 2021-05-07 | 中南大学 | Method for simultaneously improving strength and plasticity of 2219 aluminum-based AlCoCrFeNi composite material plate |
| CN113235027A (en) * | 2021-05-21 | 2021-08-10 | 重庆理工大学 | Deformed magnesium alloy plate with good matching of strength and plasticity and preparation method thereof |
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