JP4239081B2 - Magnesium-based member and manufacturing method thereof - Google Patents
Magnesium-based member and manufacturing method thereof Download PDFInfo
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Description
本発明は、表面が被膜によって被覆されたマグネシウム系部材およびその製造方法に関するものである。 The present invention relates to a magnesium-based member whose surface is coated with a coating and a method for producing the same.
近年の軽量化ニーズの高まりにより、アルミニウムよりも軽く、実用金属中で最も軽量なマグネシウム（Ｍｇ）が構造材料等として多くの分野で注目されている。例えば、航空機・宇宙機器用材料の他、自動車用材料、家電製品用材料等として多用されつつある。また、昨今の環境意識や資源の有効活用意識の高まりに伴い、各製品のリサイクル性が強く求めらている。このような観点からも、マグネシウム合金は非常に有望な材料として期待されている。 Due to the recent increase in needs for weight reduction, magnesium (Mg), which is lighter than aluminum and lightest among practical metals, has attracted attention as a structural material in many fields. For example, in addition to materials for aircraft and space equipment, it is being widely used as materials for automobiles, materials for home appliances, and the like. In addition, with the recent increase in environmental awareness and awareness of effective use of resources, the recyclability of each product is strongly demanded. From this point of view, the magnesium alloy is expected as a very promising material.
ところが、マグネシウムは、非常に活性な金属であり、実用金属中で最も電位的に卑な金属（つまり、イオン化傾向が大きい金属）である。そして、マグネシウム自体は、耐蝕性に優れる緻密な酸化被膜を形成することもないため、純マグネシウムは勿論、マグネシウム合金も耐蝕性が非常に劣る。従って、マグネシウムやマグネシウム合金からなるマグネシウム系部材の実用化や用途拡大を図るには、その耐蝕性の確保が不可欠である。 However, magnesium is a very active metal, and is the most potential base metal among practical metals (that is, a metal having a large ionization tendency). And since magnesium itself does not form a dense oxide film having excellent corrosion resistance, magnesium alloys as well as pure magnesium are very poor in corrosion resistance. Accordingly, in order to put the magnesium-based member made of magnesium or a magnesium alloy into practical use or to expand its application, it is essential to ensure its corrosion resistance.
その方策として、通常、マグネシウム系部材等の表面に、耐蝕性に優れた被膜が設けられる。このような被膜として、例えば、リン酸塩等を用いて化学的に形成した化成被膜、マグネシウム母材を陽極としてその表面に酸化被膜を形成した陽極酸化被膜等がある。この一例は下記特許文献１に開示がある。 As a measure for this, a film having excellent corrosion resistance is usually provided on the surface of a magnesium-based member or the like. Examples of such a film include a chemical conversion film chemically formed using phosphate or the like, and an anodic oxide film having a magnesium base material as an anode and an oxide film formed on the surface thereof. An example of this is disclosed in Patent Document 1 below.
もっとも、それらの被膜は、塗装の下地として用いられることが多く、高い耐蝕性が求められる場合には、化成被膜等の上にさらに塗装が施される。ちなみに、化成被膜や陽極酸化被膜を設けるための下地処理を行わずに、部材表面に直接塗装すると、形成された塗膜は密着性が悪く、剥離等を生じ易いため、耐蝕性の確保が難しい。このため、長期間に渡る耐蝕性の確保が必要な場合には、マグネシウム系部材の表面へ直接に塗装することは従来行われていなかった。 However, these coatings are often used as a base for painting, and when high corrosion resistance is required, further coating is performed on the chemical conversion coating or the like. By the way, when coating directly on the surface of the member without applying a base treatment for providing a chemical conversion film or an anodized film, it is difficult to ensure corrosion resistance because the formed coating film has poor adhesion and easily peels off. . For this reason, when it is necessary to ensure corrosion resistance over a long period of time, coating directly on the surface of the magnesium-based member has not been conventionally performed.
しかし、塗装の下地処理として化成処理や陽極酸化処理等を行うと、マグネシウム系部材の製造コストの上昇を招くことは避けられない。また、それらの処理溶液中に環境上好ましくない物質を含む場合、その処分に多くの費用を必要とし、やはりマグネシウム系部材の製造コストを上昇させる要因となる。 However, when chemical conversion treatment or anodizing treatment is performed as a base treatment for coating, it is inevitable that the manufacturing cost of the magnesium-based member increases. In addition, when these treatment solutions contain environmentally undesirable substances, the disposal requires a large amount of cost, which also increases the manufacturing cost of the magnesium-based member.
本発明は、このような事情に鑑みて為されたものである。すなわち、従来必要と考えられていた下地処理を省略しても、耐蝕性に優れた被膜（例えば、塗膜）が母材表面に安定して付着しているマグネシウム系部材を提供することを目的とする。また、その製造に適したマグネシウム系部材の製造方法を提供することを目的とする。 The present invention has been made in view of such circumstances. That is, an object of the present invention is to provide a magnesium-based member in which a coating (for example, coating) excellent in corrosion resistance is stably adhered to the surface of a base material even if the ground treatment that has been considered to be necessary is omitted. And Moreover, it aims at providing the manufacturing method of the magnesium-type member suitable for the manufacture.
本発明者はこの課題を解決すべく鋭意研究し、試行錯誤を重ねた結果、マグネシウム系部材の表面に、例えば、バリ取り、離型材除去等のために行うショット処理を、特定のショット材を用いて実施することで、下地処理を省略しても耐蝕性に優れた部材を提供することができることを新たに見出し、本発明を完成するに至った。 As a result of extensive research and trial and error, the present inventor has conducted a shot process for deburring, removing a release material, etc. on the surface of a magnesium-based member, and using a specific shot material. By carrying out the present invention, it has been newly found that a member excellent in corrosion resistance can be provided even if the base treatment is omitted, and the present invention has been completed.
（マグネシウム系部材）
すなわち、本発明のマグネシウム系部材は、Ｍｇを主成分とするマグネシウム系母材と、該マグネシウム系母材の少なくとも一部の表面を被覆する被膜とからなるマグネシウム系部材であって、前記被膜は、前記マグネシウム系母材の表面に亜鉛（Ｚｎ）を主成分とするビッカース硬さ（ＨＶ）が４０〜５０ＨＶの亜鉛系ショットを投射して形成された投射面を直接的に被覆するものであることを特徴とする。
(Magnesium-based material)
That is, the magnesium-based member of the present invention is a magnesium-based member composed of a magnesium-based base material containing Mg as a main component and a film covering at least a part of the surface of the magnesium-based base material. The projection surface formed by projecting a zinc-based shot having a Vickers hardness (HV) of 40 to 50 HV mainly composed of zinc (Zn) on the surface of the magnesium-based base material is directly covered. It is characterized by that.
本発明のマグネシウム系部材は、化成処理等の特殊な下地処理を行わずに、亜鉛系ショットを用いて投射した投射面へ直接的に被膜するだけで、腐蝕環境下でも優れた耐蝕性を発揮する。また、その被膜は、マグネシウム系部材の母材（マグネシウム系母材）表面に強固に密着しており、容易に剥離等することがなく、十分な耐久性を有する。 The magnesium-based member of the present invention exhibits excellent corrosion resistance even in a corrosive environment simply by coating directly onto the projection surface projected using a zinc-based shot without performing a special ground treatment such as chemical conversion treatment. To do. Further, the coating is firmly adhered to the surface of the base material (magnesium base material) of the magnesium-based member, and does not easily peel off and has sufficient durability.
本発明のマグネシウム系部材がこのような優れた耐食性を発現するメカニズムは必ずしも明らかではないが、現状、次のように考えられる。 Although the mechanism by which the magnesium-based member of the present invention exhibits such excellent corrosion resistance is not necessarily clear, the present situation is considered as follows.
亜鉛系ショットを投射した投射面は、その投射によって多かれ少なかれ表面に凹凸が形成される。また、亜鉛系ショットは、マグネシウム系母材の表面との動的な接触（例えば、擦れ、食い込み等）によって多かれ少なかれ亜鉛系ショットの構成材料（主にＺｎ）がその表面に残留する。本発明の場合、このような投射面における表面性状が被膜の密着性（つまり耐久性）やマグネシウム系部材の耐蝕性に大きく影響していると考えられる。本発明者は、この点に着目して鋭意研究調査した結果、そのような投射面の表面性状とマグネシウム系部材の耐食性等との相関を次のように考えるに至った。 On the projection surface on which the zinc-based shot is projected, unevenness is formed on the surface more or less by the projection. In addition, the zinc-based shot has a more or less constituent material (mainly Zn) remaining on the surface due to dynamic contact (for example, rubbing, biting, etc.) with the surface of the magnesium-based base material. In the case of the present invention, it is considered that such a surface property on the projection surface greatly affects the adhesion (that is, durability) of the coating and the corrosion resistance of the magnesium-based member. As a result of diligent research and investigation focusing on this point, the present inventor came to consider the correlation between the surface properties of such a projection surface and the corrosion resistance of the magnesium-based member as follows.
最初に、投射面の表面に形成された凹凸の程度（つまり、表面粗さ）の耐蝕性への影響について説明する。マグネシウム系母材は、純Ｍｇまたは種々の合金元素を含むＭｇ合金からなる。それらの組成が何であれ、マグネシウム系母材は通常、鋼材、ステンレス材またはガラス材等に比較して軟質である。このマグネシウム系母材の表面に、従来のような、鋼材、ステンレス材（ＳＵＳ材）またはガラス材等からなるショットを投射すれば、マグネシウム系母材の表面に相当深い凹凸が形成されて、その投射面の表面粗さは非常に粗いものとなってしまう。 First, the influence of the degree of unevenness (that is, the surface roughness) formed on the surface of the projection surface on the corrosion resistance will be described. The magnesium-based base material is made of pure Mg or an Mg alloy containing various alloy elements. Whatever their composition, magnesium-based base materials are usually softer than steel materials, stainless steel materials or glass materials. If a shot made of steel, stainless steel (SUS material), glass material, or the like is projected onto the surface of the magnesium-based base material, considerably deep irregularities are formed on the surface of the magnesium-based base material. The surface roughness of the projection surface is very rough.
ところが、Ｚｎを主成分とする亜鉛系ショットは、その化学組成等にも依るが、鋼材、ＳＵＳ材等からなるショットよりも十分に軟質であり、マグネシウム系母材と硬さも近い。従って、この亜鉛系ショットをマグネシウム系母材の表面に投射した場合、亜鉛系ショットは変形し易く、マグネシウム系母材の表面にできる凹凸の程度、つまり、その表面粗さも比較的小さいものとなる。しかも、本発明者が種々の実験を繰返したところ、マグネシウム系母材の表面粗さ（Ｒａ）は、亜鉛系ショットの粒径やその投射条件によってあまり影響を受けないことも確認されている。 However, a zinc-based shot containing Zn as a main component is sufficiently softer than a shot made of a steel material, a SUS material, or the like, and has a hardness close to that of a magnesium-based base material. Therefore, when this zinc-based shot is projected onto the surface of the magnesium-based base material, the zinc-based shot is easily deformed, and the degree of unevenness formed on the surface of the magnesium-based base material, that is, the surface roughness is relatively small. . Moreover, when the present inventors repeated various experiments, it has been confirmed that the surface roughness (Ra) of the magnesium-based base material is not significantly affected by the particle size of the zinc-based shot and the projection conditions.
このように、マグネシウム系母材の表面に亜鉛系ショットを投射した場合、その表面には微細な凹凸が形成されるものの、その凹凸の高低差、つまり表面粗さは、ＳＵＳ材のショット等を投射した場合に比べて、十分に小さいものとなる。しかも、この表面にできる凹凸の高低差、つまり、表面粗さが小さい程、マグネシウム系母材が腐蝕されづらくなることを、本発明者は種々の試験を通じて確認している。このような現象が生じる理由は現状定かではないが、マグネシウム系母材の表面積の増大とその表面にできた凹凸の高低差に応じて電位差が生じ、その電位差によって腐蝕（電蝕）が進行するためと考えられる。従って、本発明のように、亜鉛系ショットの投射によって形成される投射面の凹凸の高低差が小さい場合、その間に生じる電位差も小さくなり、それに伴う電蝕も進行し難い。このことが、マグネシウム系部材の耐蝕性の向上に大きく寄与していると考えられる。 As described above, when a zinc-based shot is projected onto the surface of the magnesium-based base material, fine unevenness is formed on the surface, but the unevenness of the unevenness, that is, the surface roughness is the same as the shot of SUS material. Compared to the case of projection, it is sufficiently small. In addition, the present inventor has confirmed through various tests that the difference in height of the unevenness formed on the surface, that is, the smaller the surface roughness, the harder the magnesium base material is to be corroded. The reason why such a phenomenon occurs is not clear at present, but a potential difference occurs according to the increase in the surface area of the magnesium-based base material and the height difference of the irregularities formed on the surface, and corrosion (electric corrosion) proceeds due to the potential difference. This is probably because of this. Therefore, as in the present invention, when the height difference of the projections and depressions formed by the projection of the zinc-based shot is small, the potential difference generated therebetween becomes small, and the electric corrosion associated therewith hardly progresses. This is considered to have greatly contributed to the improvement of the corrosion resistance of the magnesium-based member.
次に、投射面の表面に残存する亜鉛系ショットの構成材料の耐蝕性への影響について説明する。マグネシウム系母材の表面にショットを投射すれば、ショットの種類に拘らず、多かれ少なかれショットの構成材料がマグネシウム系母材の表面に残存する。各種金属はそれぞれ固有の電位をもっているところ、Ｍｇと他の金属とが接触すると、当然に両者間には電位差を生じる。この電位差は、前述したように、電蝕の原因となる。特に、Ｍｇは実用金属中でもっとも電位が卑な金属であるため、この電位差が大きくなる傾向にあり、Ｍｇを主成分とするマグネシウム系母材は電蝕し易い。従って、このマグネシウム系母材の電蝕を抑制するには、可能な限り、その電位差を小さくするのが好ましい。ここで、本発明で用いた亜鉛系ショットの主成分であるＺｎは、実用金属中で最も腐蝕電位の小さいＭｇとの電位差が小さい。このため、そのショットの構成材料がマグネシウム系母材の表面に残存したとしても、マグネシウム系母材表面での電蝕は非常に少ない。ちなみに、各金属の海水中における自然電位の一例を挙げると、Ｍｇ：−１．５Ｖ、Ｚｎ：−１．０３Ｖ、ＳＵＳ４３０：−０．５７Ｖである。亜鉛系ショットの主成分であるＺｎとマグネシウム系母材の主成分であるＭｇとの間で生じる電位差が、ショット材として従来から多用されてるＳＵＳ材の場合と比較して、如何に小さいかが解る。このように本発明では、亜鉛系ショットの残留物をマグネシウム系母材の表面からわざわざ除去しなくても、マグネシウム系母材の表面で生じる異種金属間の電位差が非常に小さく、電蝕の進行が非常に抑制されたと考えられる。このことも、マグネシウム系部材の耐蝕性の向上に大きく寄与していると考えられる。 Next, the influence on the corrosion resistance of the constituent material of the zinc-based shot remaining on the surface of the projection surface will be described. If a shot is projected onto the surface of the magnesium-based base material, the constituent material of the shot remains on the surface of the magnesium-based base material regardless of the type of shot. Each metal has a unique potential, and when Mg and another metal come into contact with each other, a potential difference is naturally generated between them. This potential difference causes galvanic corrosion as described above. In particular, Mg has the lowest potential among practical metals, so this potential difference tends to increase, and a magnesium-based base material containing Mg as a main component is easily eroded. Therefore, in order to suppress the electrolytic corrosion of the magnesium base material, it is preferable to reduce the potential difference as much as possible. Here, Zn, which is the main component of the zinc-based shot used in the present invention, has a small potential difference from Mg having the smallest corrosion potential among practical metals. For this reason, even if the constituent material of the shot remains on the surface of the magnesium base material, there is very little electric corrosion on the surface of the magnesium base material. By the way, an example of the natural potential of each metal in seawater is Mg: −1.5V, Zn: −1.03V, SUS430: −0.57V. How small is the potential difference generated between Zn, which is the main component of the zinc-based shot, and Mg, which is the main component of the magnesium-based base material, compared to the SUS material that has been frequently used as a shot material. I understand. As described above, according to the present invention, the potential difference between different metals generated on the surface of the magnesium-based base material is very small and the progress of electrolytic corrosion without removing the zinc-based shot residue from the surface of the magnesium-based base material. Is considered to be greatly suppressed. This is also considered to contribute greatly to the improvement of the corrosion resistance of the magnesium-based member.
これまでは、マグネシウム系母材に亜鉛系ショットを投射した投射面における直接的な腐蝕傾向を説明してきた。ところが、本発明者がさらに研究したところ、その腐蝕傾向は、投射面に塗装して塗膜を形成した場合であっても同様の傾向を示すことが確認されている。 Until now, the direct corrosion tendency in the projection surface which projected the zinc-type shot on the magnesium-type base material has been demonstrated. However, as a result of further research by the present inventors, it has been confirmed that the corrosion tendency shows the same tendency even when the projection surface is coated to form a coating film.
また、上記亜鉛系ショットによる投射面に塗膜等を直接的に設けた場合と、亜鉛系ショットを投射していない鋳肌面等に直接的に塗膜を設けた場合とを比較すると、ショットを投射していない鋳肌面には離型材が残っているため密着性が悪く、前者の塗膜の方が遙かに優れた耐蝕性を示すことも本発明者は確認している。しかもその耐蝕性や耐久性は、ＳＵＳ４３０投射後の下地処理を施した場合と同等以上であった。こうして、本発明のマグネシウム系部材は、ショット投射後のマグネシウム系母材に下地処理等を施さずに、塗膜等の被膜を直接的に形成した場合であっても、長期間、優れた耐蝕性を示したと考えられる。 Moreover, when comparing the case where a coating film or the like is directly provided on the projection surface by the zinc-based shot and the case where a coating film is directly provided on a casting surface or the like where no zinc-based shot is projected, the shot The present inventor has also confirmed that the mold release material remains on the cast skin surface on which no film is projected, so that the adhesion is poor, and the former coating film exhibits much better corrosion resistance. Moreover, the corrosion resistance and durability were equal to or higher than those obtained when the ground treatment after SUS430 projection was performed. Thus, the magnesium-based member of the present invention has excellent corrosion resistance over a long period of time, even when a film such as a coating film is directly formed without subjecting the magnesium-based base material after shot projection to a ground treatment. It is thought that it showed gender.
なお、被膜が投射面との密着性に優れる理由は定かではないが、亜鉛系ショットの投射によって、投射面に残存する離型材等が除去されると共に投射面の表面にその表面粗さが荒れない程度の微細な凹凸が形成されるためと考えられる。 Although the reason why the coating film has excellent adhesion to the projection surface is not clear, the release material remaining on the projection surface is removed and the surface roughness of the projection surface is roughened by the projection of the zinc-based shot. This is thought to be due to the formation of fine irregularities that are not present.
（マグネシウム系部材の製造方法）
本発明は、マグネシウム系部材に限らずその製造方法としても把握でき、上記マグネシウム系部材は例えば次のような製造方法によって製造され得る。
すなわち、本発明は、Ｍｇを主成分とするマグネシウム系母材の表面にＺｎを主成分とするビッカース硬さ（ＨＶ）が４０〜５０ＨＶの亜鉛系ショットを投射する投射工程と、該亜鉛系ショットが投射されてできた投射面の少なくとも一部を直接的に被覆する被膜を形成する被覆工程とを備えてなり、該マグネシウム系母材の少なくとも一部の表面が該被膜で被覆されたマグネシウム系部材が得られることを特徴とするマグネシウム系部材の製造方法としても良い。
(Manufacturing method of magnesium-based member)
The present invention can be grasped not only as a magnesium-based member but also as a manufacturing method thereof, and the magnesium-based member can be manufactured by, for example, the following manufacturing method.
That is, the present invention includes a projecting step of projecting a zinc-based shot having a Vickers hardness (HV) of 40 to 50 HV containing Zn as a main component on the surface of a magnesium-based base material containing Mg as a main component, and the zinc-based shot. And a coating process for directly forming at least a part of the projection surface formed by projecting the projection, and a magnesium system in which at least a part of the surface of the magnesium base material is coated with the film It is good also as a manufacturing method of the magnesium-type member characterized by the member being obtained.
なお、本明細書でいう「直接的に」被覆するとは、化成処理や陽極酸化処理のような特殊な下地処理を投射面に施さずに被覆する、という意味である。また、「被膜」の代表的なものは、塗装後に形成される塗膜であるが、本発明の被膜は塗膜に限られずものではない。耐蝕性向上に効果のある被膜であれば、その種類等は問わない。例えば、塗膜以外の樹脂被膜等であっても良い。 Note that “directly” coating in the present specification means that the projection surface is coated without performing a special ground treatment such as chemical conversion treatment or anodizing treatment. A representative “coating film” is a coating film formed after painting, but the coating film of the present invention is not limited to a coating film. The type of the coating is not particularly limited as long as it is effective for improving the corrosion resistance. For example, a resin coating other than the coating may be used.
また、本明細書でいう「マグネシウム系」とは、純マグネシウムまたはマグネシウム合金を意味し、マグネシウム系母材は、被膜をもうける部分が少なくとも純マグネシウムまたはマグネシウム合金から構成されていれば良い。マグネシウム系部材は、そのようなマグネシウム系母材とその表面に設けられた被膜とを少なくとも備えれば良い。従って、マグネシウム系部材は、部材全体がマグネシウムまたはマグネシウム合金から形成されている必要はない。例えば、骨格部分が樹脂等の他の材質から構成された複合材料であっても良い。 In addition, “magnesium-based” in the present specification means pure magnesium or a magnesium alloy, and the magnesium-based base material only needs to be composed of at least pure magnesium or a magnesium alloy. The magnesium-based member may include at least such a magnesium-based base material and a coating provided on the surface thereof. Therefore, the magnesium-based member does not have to be formed entirely of magnesium or a magnesium alloy. For example, a composite material in which the skeleton portion is made of another material such as a resin may be used.
発明の実施形態を挙げて、本発明をより詳しく説明する。なお、以下の実施形態を含め、本明細書で説明する内容は、本発明に係るマグネシウム系部材のみならず、その製造方法にも、適宜適用できるものであることを断っておく。また、いずれの実施形態が最良であるか否かは、対象、要求性能等によって異なることを断っておく。 The present invention will be described in more detail with reference to embodiments of the invention. It should be noted that the contents described in the present specification, including the following embodiments, can be appropriately applied not only to the magnesium-based member according to the present invention but also to the manufacturing method thereof. Also, it should be noted that which embodiment is the best depends on the target, required performance, and the like.
（１）マグネシウム系母材
マグネシウム系母材は、材質、形態、製法等を問わず、少なくとも、本発明の被膜が設けられる部分に存在すれば足る。例えば、マグネシウム系母材は、鍛造品でも鋳造品（マグネシウム系鋳物）でも良い。鋳造品の場合、砂型鋳造、金型鋳造、ダイキャスト鋳造、射出成形等のいずれによって得られたものでも良い。もっとも、量産性、コスト等を勘案すると、マグネシウム系母材の多くはダイキャスト鋳造品となる。マグネシウム系母材が鋳造品の場合、いずれの鋳造方法を採用したとしても、多かれ少なかれバリ等が発生し易い。このバリ等を除去するために、従来はショットブラスト等が行われていた。このショットブラストで本発明の亜鉛系ショットを使用すれば、投射面の形成とマグネシウム系母材のバリ等を兼ねることができるので好都合である。この場合、本発明でいう亜鉛系ショットを投射する投射工程は、マグネシウム系母材からバリ等を除去するためのショットブラスト工程ともなる。
(1) Magnesium-based base material The magnesium-based base material is sufficient if it exists at least in the portion where the coating film of the present invention is provided, regardless of the material, form, manufacturing method, and the like. For example, the magnesium-based base material may be a forged product or a cast product (magnesium-based cast product). In the case of a cast product, it may be obtained by any of sand mold casting, mold casting, die casting, injection molding and the like. However, considering mass productivity and cost, most of the magnesium-based base materials are die cast products. When the magnesium-based base material is a cast product, no matter which casting method is employed, burrs or the like are more or less likely to occur. Conventionally, shot blasting or the like has been performed to remove the burrs and the like. If the zinc-based shot of the present invention is used in this shot blasting, it is advantageous because it can serve as the formation of the projection surface and the burr of the magnesium-based base material. In this case, the projecting step of projecting a zinc-based shot according to the present invention also serves as a shot blasting step for removing burrs and the like from the magnesium-based base material.
マグネシウム系母材の成分組成は、その主成分がＭｇである限り、その他の合金元素を問わない。マグネシウム系母材に要求される強度、耐蝕性等の観点から適当な合金元素および含有量が選択される。その合金元素にはＡｌ、Ｃａ、Ｍｎ、Ｚｎ、Ｒ．Ｅ．（希土類元素）等がある。 The component composition of the magnesium-based base material may be any other alloy element as long as the main component is Mg. An appropriate alloy element and content are selected from the viewpoints of strength and corrosion resistance required for the magnesium-based base material. The alloy elements include Al, Ca, Mn, Zn, R.I. E. (Rare earth elements).
（２）亜鉛系ショット
亜鉛系ショットは、主成分をＺｎとするショットであり、組成、形態、硬度等は問わない。例えば、その成分組成として、Ｚｎ以外にＡｌ、Ｍｎ等の合金元素を適量含有していても良い。もっとも、マグネシウム系母材の表面にショットが残存した際に、電位差を拡大するような合金元素は含まない方が好ましい。また、マグネシウム系母材との硬度差が著しく拡大しないように、合金元素やその範囲を選択するのが好ましい。
(2) Zinc-based shot A zinc-based shot is a shot containing Zn as a main component, and the composition, form, hardness and the like are not limited. For example, the component composition may contain an appropriate amount of alloy elements such as Al and Mn in addition to Zn. However, it is preferable not to include an alloy element that expands the potential difference when shots remain on the surface of the magnesium-based base material. Moreover, it is preferable to select an alloy element and its range so that the hardness difference from the magnesium base material does not significantly increase.
亜鉛系ショットの硬さを具体的に挙げれば、例えば、ビッカース硬さ（ＨＶ）で１５０ＨＶ以下であるのが好ましい。その下限は特に限定されない。ただし、純Ｚｎ（Ｚｎが９９％以上）のショットの場合、その硬さは４０〜５０ＨＶ程度であり、マグネシウム系母材の硬さは５０〜７０ＨＶ程度である。そこで、亜鉛系ショットの硬さは、４０ＨＶ以上が好ましい。亜鉛系ショットの硬さは、マグネシウム系母材の硬さに近い方が好ましく、亜鉛系ショットの硬さがあまり小さいと、亜鉛系ショットの寿命が短くなるからである。 Specifically, the hardness of the zinc-based shot is preferably, for example, 150 HV or less in terms of Vickers hardness (HV). The lower limit is not particularly limited. However, in the case of a shot of pure Zn (Zn is 99% or more), the hardness is about 40 to 50 HV, and the hardness of the magnesium-based base material is about 50 to 70 HV. Therefore, the hardness of the zinc-based shot is preferably 40 HV or more. The hardness of the zinc-based shot is preferably close to the hardness of the magnesium-based base material, and if the hardness of the zinc-based shot is too small, the life of the zinc-based shot is shortened.
亜鉛系ショットの粒径は拘らないが、０．４〜０．６ｍｍ程度であれば良い。その粒径が過小であるとバリ取り等を行う上で好ましくなく、過大であると鋳肌が荒れて好ましくないからである。また、亜鉛系ショットの粒形状は、球状でも長粒状でも良いが、尖った部分が少ない方が好ましい。亜鉛系ショットの表面に尖鋭的な部分が少ないと、マグネシウム系母材の投射面の表面も滑らかとなり、凹凸の高低差も小さくなって耐蝕性が向上すると考えられるからである。 The particle size of the zinc-based shot is not limited, but may be about 0.4 to 0.6 mm. This is because if the particle size is too small, it is not preferable for deburring and the like, and if it is too large, the casting surface becomes rough, which is not preferable. The grain shape of the zinc-based shot may be spherical or long-grained, but it is preferable that there are few sharp parts. This is because if there are few sharp parts on the surface of the zinc-based shot, the surface of the projection surface of the magnesium-based base material will be smooth, the unevenness of the unevenness will be reduced, and the corrosion resistance will be improved.
（３）投射面
投射面は、マグネシウム系母材の表面に亜鉛系ショットを投射して形成された面である。前述したように、この投射面にできた凹凸の高低差が小さい方がマグネシウム系部材の耐蝕性が向上する。例えば、その表面粗さは、中心線平均粗さ（Ｒａ）で１．０μｍ以下、さらには、０．７μｍ以下であると好ましい。亜鉛系ショットを使用する限り、投射面の表面粗さは、その粒径や投射速度等にはあまり影響されない。どの程度の間、亜鉛系ショットを投射するかは、マグネシウム系部材に要求される特性（強度、耐蝕性、製造コスト等）に応じて決定すれば良い。
(3) Projection surface The projection surface is a surface formed by projecting a zinc-based shot onto the surface of a magnesium-based base material. As described above, the corrosion resistance of the magnesium-based member is improved when the unevenness of the unevenness formed on the projection surface is smaller. For example, the surface roughness is preferably 1.0 μm or less, and more preferably 0.7 μm or less in terms of centerline average roughness (Ra). As long as the zinc-based shot is used, the surface roughness of the projection surface is not significantly affected by the particle size, the projection speed, and the like. The extent to which the zinc-based shot is projected may be determined according to characteristics (strength, corrosion resistance, manufacturing cost, etc.) required for the magnesium-based member.
投射面は、亜鉛系ショットの投射によってバリ等が除去される。この投射面には、亜鉛系ショットの構成材料が部分的に残存するが、前述したように、亜鉛系ショットとマグネシウム系母材との間の電位差は小さい。従って、亜鉛系ショットの構成材料が投射面に残存していても、マグネシウム系母材が大きく腐蝕されることはない。従って、あえてその残存したショット材を除去する必要はないが、この投射面に被膜を形成する前に、予めその投射面を脱脂、洗浄等して、残留したショット材を除去しておいても良いことはいうまでもない。 Burrs and the like are removed from the projection surface by the projection of the zinc-based shot. Although the constituent material of the zinc-based shot partially remains on the projection surface, the potential difference between the zinc-based shot and the magnesium-based base material is small as described above. Therefore, even if the constituent material of the zinc-based shot remains on the projection surface, the magnesium-based base material is not greatly corroded. Therefore, it is not necessary to dare to remove the remaining shot material, but before forming a film on this projection surface, the projection surface may be degreased and washed in advance to remove the remaining shot material. It goes without saying that it is good.
投射面は、亜鉛系ショットの投射によって、多かれ少なかれ塑性変形して表面に凹凸が形成される。このような塑性変形によって、マグネシウム系母材の表層部分には圧縮残留応力が付与される。圧縮残留応力の付与は、マグネシウム系母材の強度や耐疲労性の向上に有効である。この場合、本発明でいう亜鉛系ショットの投射工程は、ショットピーニング工程とも考えられる。 The projection surface is more or less plastically deformed by projection of the zinc-based shot, and irregularities are formed on the surface. By such plastic deformation, compressive residual stress is applied to the surface layer portion of the magnesium-based base material. The application of compressive residual stress is effective in improving the strength and fatigue resistance of the magnesium-based base material. In this case, the zinc-based shot projecting process referred to in the present invention may be considered as a shot peening process.
（４）被膜
被膜は、投射面に直接的に形成されるものであり、マグネシウム系母材の腐蝕を抑止するものである。この被膜は、例えば、投射面に塗料を直接的に付着させた塗膜である。この場合、本発明の被覆工程は投射面に塗料を直接的に付着させる塗装工程となる。塗装方法に種々あるが、工業的には（カチオン）電着塗装や粉体（溶剤）塗装等がある。
(4) Coating The coating is formed directly on the projection surface and suppresses the corrosion of the magnesium base material. This coating film is, for example, a coating film in which a paint is directly attached to the projection surface. In this case, the coating process of the present invention is a coating process in which the paint is directly attached to the projection surface. There are various coating methods, but industrially, there are (cation) electrodeposition coating, powder (solvent) coating, and the like.
電着塗装とは、例えば、被塗物を水溶性塗料中に浸積して、その被塗物（マグネシウム系母材）を陰極にし、塗料を陽極として直流電圧を印加して、被塗物の表面に塗膜を形成される塗装方法である。この電着塗装を行うと、塗料はマグネシウム系母材の投射面の微細な空隙にまで浸透し、全面的に均一な塗膜が形成される。しかも、マグネシウム系母材を塗料溶液から引上げたときに形成されている塗膜は、水に不溶でかつ含水率の低いものとなっており、非常に好ましい。また、塗着効率９５％以上であり経済性に優れ、完全な焼付け塗装を行うこともできる。この場合、本発明でいう塗装工程は、電着塗装工程となる。 Electrodeposition coating means, for example, immersing an object to be coated in a water-soluble paint, using the object to be coated (magnesium base material) as a cathode, applying a DC voltage with the paint as an anode, It is the coating method in which a coating film is formed on the surface. When this electrodeposition coating is performed, the paint penetrates into the fine gaps on the projection surface of the magnesium base material, and a uniform coating film is formed on the entire surface. Moreover, the coating film formed when the magnesium-based base material is pulled up from the coating solution is very preferable because it is insoluble in water and has a low water content. In addition, the coating efficiency is 95% or more, which is excellent in economic efficiency and can be completely baked. In this case, the coating process referred to in the present invention is an electrodeposition coating process.
粉体（溶剤）塗装とは、吹きつけ塗装等によって、被塗物の表面に有機質の連続被膜を形成する方法である。静電塗装を行う場合には、静電発生機で得られた直流高電圧により粉体塗料を帯電させ、被塗物をアースしておいて、その被塗物に静電引力により塗料を付着させる方法である。被塗物に塗着した粉体塗料は、焼付炉等で加熱溶融、硬化させて連続被膜とすることができる。
勿論、本発明でいう塗装方法は、上述したような塗装方法に限定されるものではなく、刷毛塗り等による塗装であっても良い。
Powder (solvent) coating is a method of forming an organic continuous film on the surface of an object to be coated by spray coating or the like. When electrostatic coating is performed, the powder coating is charged by the direct current high voltage obtained by the electrostatic generator, the substrate is grounded, and the coating is attached to the substrate by electrostatic attraction. It is a method to make it. The powder coating material applied to the object to be coated can be heated and melted and cured in a baking furnace or the like to form a continuous film.
Of course, the coating method referred to in the present invention is not limited to the above-described coating method, and may be coating by brushing or the like.
さらに、本発明でいう被膜は、上記塗膜に限らず、マグネシウム系母材の耐蝕性を向上させるものであればその種類を問わない。従って、被膜は、塗膜以外の樹脂層や電解めっきや無電解めっき等によって形成されためっき層であっても良いし、さらには、陽極酸化層や化成被膜等であっても良い。 Furthermore, the coating film referred to in the present invention is not limited to the above coating film, and any type can be used as long as it improves the corrosion resistance of the magnesium-based base material. Therefore, the coating film may be a resin layer other than the coating film, a plating layer formed by electrolytic plating, electroless plating, or the like, or may be an anodized layer or a chemical conversion film.
実施例を挙げて、本発明をより具体的に説明する。
（試験片の製造）
試験片として、Ｍｇ−Ａｌ系溶湯を金型に注湯して自然凝固させたＭｇ合金試験片（マグネシウム系母材）を用意した。この試験片に各種のショットを投射した。使用したショットの材質、硬さ、粒径等は表１に示した。投射は、遠心投射機（新東ブレータ社製のブラスト装置）を用いて行った（投射工程）。各ショット材を投射後の試験片の表面（投射面）の粗さ（Ｒａ）を測定した。その結果を表１に併せて示した。なお、表面粗さを測定する際のパラメータの算出規格はＪＩＳ−’８２規格に準拠した。
The present invention will be described more specifically with reference to examples.
(Manufacture of test pieces)
As a test piece, an Mg alloy test piece (magnesium base material) prepared by pouring Mg—Al-based molten metal into a mold and spontaneously solidifying it was prepared. Various shots were projected on the test piece. The material, hardness, particle size, etc. of the shot used are shown in Table 1. Projection was performed using a centrifugal projector (a blast device manufactured by Shinto Blator Co., Ltd.) (projection process). The roughness (Ra) of the surface (projection surface) of the test piece after each shot material was projected was measured. The results are also shown in Table 1. In addition, the calculation standard of the parameter at the time of measuring surface roughness followed the JIS-'82 standard.
投射工程後の各試験片に、電着塗装を行った（電着塗装工程）。これにより、表面が厚さ約１５〜２０μｍの塗膜で被覆された試験片（マグネシウム系部材）を得た。 Electrodeposition coating was performed on each test piece after the projection process (electrodeposition coating process). This obtained the test piece (magnesium-type member) by which the surface was coat | covered with the coating film about 15-20 micrometers thick.
（評価試験）
上記のようにして得られた各試験片について、塩水噴霧試験を行った。この試験方法は、ＪＩＳ Ｚ２３７１に規定されている方法に従った。この塩水噴霧試験を２５０時間行った後の腐蝕減量比（％）を表１に併せて示した。ちなみに、腐蝕減量比（％）は、次のようにして求めた。
(Evaluation test)
A salt spray test was performed on each test piece obtained as described above. This test method followed the method prescribed in JIS Z2371. Table 1 also shows the corrosion weight loss ratio (%) after the salt spray test was conducted for 250 hours. Incidentally, the corrosion weight loss ratio (%) was determined as follows.
腐蝕減量比（％）＝腐蝕減量（ｇ）／元重量（ｇ） ｘ１００
参考として、ＳＵＳ４３０のショットを投射した投射面に、化成処理または含浸処理からなる下地処理を行った後に電着塗装を行った場合の腐蝕減量比（％）も併せて示した。なお、この化成処理は、脱脂、エッチングした後に行った。また、含浸処理は、市販の樹脂を入れた含浸槽中で、１０〜２０℃ｘ２０分間保持して行った。
Corrosion weight loss ratio (%) = corrosion weight loss (g) / original weight (g) × 100
As a reference, the corrosion weight loss ratio (%) when the electrodeposition coating was performed after the ground treatment including the chemical conversion treatment or the impregnation treatment was performed on the projection surface on which the shot of SUS430 was projected was also shown. This chemical conversion treatment was performed after degreasing and etching. Moreover, the impregnation process was performed by hold | maintaining for 10-20 degreeC x 20 minutes in the impregnation tank which put commercially available resin.
（評価）
表１から明らかなように、本発明のように亜鉛系ショットの投射面に電着塗装したものは、その腐蝕減量比が非常に小さくなっている。しかも、その腐蝕減量比は、ＳＵＳ４３０ショットの投射面に下地処理を行った下地面に、電着塗装行ったものよりも耐蝕性に優れていることが確認された。
(Evaluation)
As is clear from Table 1, the corrosion weight loss ratio of the electrodeposited zinc-shot shot surface as in the present invention is very small. In addition, it was confirmed that the corrosion weight loss ratio is superior to the corrosion resistance of the base surface obtained by subjecting the SUS430 shot projection surface to the base surface treatment and electrodeposition coating.
ちなみに、各ショットをマグネシウム系母材に投射した後、電着塗装を行わずに、上述の塩水噴霧試験を８時間行って、その場合の腐蝕減量比を同様に求めた。各ショット毎の腐蝕減量比の大小関係は、電着塗装をした場合と同傾向を示すことを本発明者は確認している。従って、電着塗装後の耐蝕性の良否は、投射面の性状に大きく起因していると考えられた。 By the way, after each shot was projected onto the magnesium base material, the above-mentioned salt spray test was conducted for 8 hours without performing electrodeposition coating, and the corrosion weight loss ratio in that case was similarly determined. The present inventor has confirmed that the magnitude relationship between the corrosion weight loss ratios for each shot shows the same tendency as in the case of electrodeposition coating. Therefore, the quality of the corrosion resistance after electrodeposition coating was considered to be largely attributable to the properties of the projection surface.
Claims (8)
前記被膜は、前記マグネシウム系母材の表面に亜鉛（Ｚｎ）を主成分とするビッカース硬さ（ＨＶ）が４０〜５０ＨＶの亜鉛系ショットを投射して形成された投射面を、直接的に被覆するものであることを特徴とするマグネシウム系部材。 A magnesium-based member comprising a magnesium-based base material containing magnesium (Mg) as a main component and a coating covering at least a part of the surface of the magnesium-based base material,
The coating directly covers a projection surface formed by projecting a zinc-based shot having a Vickers hardness (HV) of 40 to 50 HV mainly composed of zinc (Zn) on the surface of the magnesium-based base material. A magnesium-based member characterized by the above.
該亜鉛系ショットが投射されてできた投射面の少なくとも一部を直接的に被覆する被膜を形成する被覆工程とを備えてなり、
該マグネシウム系母材の少なくとも一部の表面が該被膜で被覆されたマグネシウム系部材が得られることを特徴とするマグネシウム系部材の製造方法。 A projecting step of projecting a zinc-based shot having a Vickers hardness (HV) of 40 to 50 HV containing Zn as a main component on the surface of a magnesium-based base material containing Mg as a main component;
A coating step of forming a coating that directly covers at least a part of a projection surface formed by projecting the zinc-based shot,
A method for producing a magnesium-based member, wherein a magnesium-based member in which at least a part of the surface of the magnesium-based base material is coated with the coating film is obtained.
前記被膜は塗膜である請求項５に記載のマグネシウム系部材の製造方法。 The coating step is a coating step in which paint is directly attached to the projection surface,
The method for producing a magnesium-based member according to claim 5 , wherein the coating is a coating.
前記投射工程はショットブラスト工程である請求項５に記載のマグネシウム系部材の製造方法。 The magnesium base material is a magnesium casting,
The method for manufacturing a magnesium-based member according to claim 5 , wherein the projecting step is a shot blasting step.
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