CN110699578B

CN110699578B - High-zinc low-copper aluminum alloy with excellent corrosion resistance and preparation method thereof

Info

Publication number: CN110699578B
Application number: CN201911159010.9A
Authority: CN
Inventors: 杨育奇; 严平; 司恒刚; 王磊; 肖绮; 周晨曦; 张志勇; 方嘉文
Original assignee: Jiangxi University of Science and Technology
Current assignee: Jiangxi University of Science and Technology
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2021-04-30
Anticipated expiration: 2039-11-22
Also published as: CN110699578A

Abstract

High-zinc alloy with excellent corrosion resistance,The low-copper aluminum alloy and the preparation method thereof belong to the technical field of aluminum alloy materials, and the content of each element in the metal material is Zn =10-11wt.%, Mg =1.8-2.0wt.%, Cu =0.97-1.0wt.%, Cr =0.08-0.1wt.%, Y =1.4-2.0wt.%, and Al = the balance. The corrosion of the alloy grain boundary phase is greatly inhibited, and the corrosion resistance is greatly improved and is close to the level of pure aluminum. The alloy of the invention can reach about 195N/mm under the grain size of 30um²Corresponding to a tensile strength of about 630 MPa.

Description

High-zinc low-copper aluminum alloy with excellent corrosion resistance and preparation method thereof

Technical Field

The invention belongs to the technical field of alloy materials, and particularly relates to a corrosion-resistant aluminum alloy component and a treatment method thereof.

Background

Aluminum alloys are the most widely used non-ferrous structural materials in industry and have important applications in the aerospace, automotive, mechanical manufacturing, marine and chemical industries. Among them, the 7 series Al-Zn-Mg (Cu) aluminum alloys are characterized by small density, high strength and hardness, and are particularly suitable for the aerospace industry. However, such high strength aluminum alloys often suffer from low stress embrittlement. Under the combined action of stress and an environmental medium, the failure stress is far lower than that of the material (namely tensile strength). Therefore, corrosion-resistant aluminum alloys have been an important research and development direction in structural materials for aircraft. The Zn element can be used to improve the strength of the 7-series aluminum alloy. In the 90 s of the 20 th century, a new generation of ultrahigh-strength high-zinc-aluminum alloy containing more than 8% of Zn is developed, is used for manufacturing structural members with high strength and high stress bearing capacity, and is mainly applied to the field of aerospace. However, high Zn aluminum alloys also have disadvantages such as poor plastic toughness and poor corrosion resistance. The problem of corrosion resistance of the alloy needs to be solved while maintaining high Zn content and high strength.

After Mg element is added into high-Zn alloy, Mg and Zn can form MgZn₂And the alloy has obvious strengthening effect. But not just as good as the corrosion resistance at a Zn to Mg ratio of 2. According to the report of the literature, Zn: the stress corrosion cracking resistance is the greatest when the Mg ratio is generally controlled to be about 2.7. If this ratio is exceeded, the stress corrosion resistance is reduced. Therefore, at a high Zn to Mg ratio of (>3) In the case of (2), it is necessary to effectively suppress the deterioration of the corrosion resistance of the alloy.

Cu addition also improves the strength of the aluminum alloy, and Cu is reported to have the greatest strengthening effect in aluminum among all elements. Copper has been shown to improve mechanical and cutting properties in aluminum alloys, and strength is improved primarily by solid solution strengthening and age strengthening. However, the corrosion resistance of the copper-added aluminum alloy is also lowered, and thermal cracking is likely to occur. Therefore, the copper content in aluminum alloys is typically in the range of 2.5% -5%.

According to the reports of documents, chromium can prevent the nucleation and growth of recrystallized grains in aluminum, has a certain strengthening effect on the alloy, and can improve the toughness of the alloy and reduce the stress corrosion cracking sensitivity to a certain extent.

The literature reports that rare earth elements increase the supercooling degree of components during the casting of aluminum alloy, refine grains, reduce gas and impurities in the alloy and enable the impurities to tend to be spheroidized. It is considered that the amount of the rare earth added is not excessively large, and the amount of each rare earth added is preferably about 0.1 at.%. As in the literature: plum fruitGuirong, wang hong ming, zhao yutao, cheng gang, chen bin, han sword, dong mozu, rare earth yttrium pair 7055 aluminum Mechanism of action of alloy melting and solidification process, rare metal materials and engineering, vol.39 (2010) p.80It is mentioned that the addition of 0.25 wt.% Y reduces the grain size from 60-70 um to 40-50 um. However, the literature:rare earth elements in Wang Qing Liang and Wang Daqing Effect of Yttrium on the texture and Properties of AlZnMgCu alloys, proceedings of university of mineral China, Vol.28 (1999) 382Then, it is pointed out: the addition of rare earth yttrium is not good for the aging strength and hardness of the alloy, but when the yttrium content is high<When the content of yttrium is 0.3%, the refined structure effect of yttrium is obvious, the formation of a coarse eutectic structure is inhibited, and the crack source is reduced. When the content of yttrium is large, the refining is carried outThe use is not increased any more, and a large amount of rare earth-containing compound is formed, causing discontinuity between crystal grains, increasing the possibility of crack propagation. From the reports of the literature, the effect of the rare earth on the aluminum alloy reported at present has contradiction, and the credibility of the data given by a plurality of literatures is insufficient. The main expression is that rare earth has no effect of refining grains, the addition amount of the refined grains is, the action mechanism is, and the rare earth is favorable for alloy strength or unfavorable for alloy strength, so that exact answers cannot be found in the literature at present. The reason may be that the engineering application of the aluminum alloy is mature in recent years, the depth and attention degree of the research on the aluminum alloy are far from enough, and the early domestic research on the aluminum alloy is limited by the laggard experimental means so that a plurality of contradictory conclusions still exist.

Currently, there are two main approaches to improve the corrosion resistance of aluminum alloys, one is to use a three-stage aging process of recovery and re-aging (RRA) during heat treatment, and the other is to effectively adjust the chemical composition of the alloy.

Earlier, a single-stage overaging process was often employed in 7-series aluminum alloys, which, although improving corrosion resistance, also decreased alloy strength. To overcome this drawback, B Cina (USA patent, number US3856584A) developed a tertiary aging process of recovery-reaging. At present, researchers generally consider that the RRA three-stage annealing process improves corrosion resistance (particularly stress corrosion resistance) by breaking the continuity of grain boundary phase to form discrete granular grain boundary phase at the position of grain boundary.

In addition to improving the protective effect of the oxide film on the alloy surface, the purpose of adjusting the chemical composition with respect to the corrosion capability is most important to change the electrode potential between the crystal grains and the grain boundary phase and reduce or prevent the oxidation of the grain boundary phase caused by the reaction of the corrosion galvanic cell. The electrode potentials of the crystal grains and the grain boundary phase are mainly affected by their compositions. In the 7-series aluminum alloys, the grain boundary phase may be a single phase or a plurality of phases, and the composition thereof is greatly affected by the alloying elements. Therefore, the influence of the electrode potential of the grain boundary phase on the corrosion performance of the alloy is larger than that of the grain phaseMuch more. The difference in electrode potential between the grain and grain boundary phases determines whether the grain or grain boundary phase preferentially corrodes when the galvanic cell is corroded. If the grain boundary phase preferentially corrodes, the alloy material is likely to fracture under low stress conditions. According to the literature (R. Buchheit, J. Electrochem. Soc., 142 (1995) 3994.) It is reported that the corrosion potential of Mg atoms in Al is reduced from-0.76V to-0.81V when the content of Mg atoms in Al is changed from 0 to 7wt.%, and the corrosion potential of Zn in Al is reduced from-0.76V to-0.995V when the content of Zn in Al is changed from 0 to 8 wt.%. That is, if Mg and Zn appear at grain boundaries, the corrosion potential of the grain boundary phase will decrease. For another example, documents (Bard, A. J., Parsons, R., and Jordan, J. "Standard Potentials in Aqueous Solutions," Marcel Dekker, New York, 1985.) It is reported that the electrode potential of Cu2+/Cu(s) is +0.337V, and it is presumed that if Cu remains in the grain boundary phase, the electrode potential of the grain boundary phase will rise. In the case where the electrode potential of the grain boundary phase rises, the potential difference between the crystal grains and the grain boundary phase will decrease, which contributes to a decrease in the corrosion rate of the alloy. Therefore, purposefully controlling the content of elements which are unfavorable for the corrosion performance in the grain boundary phase, such as controlling the content of Mg, Zn and other elements in the Al alloy, is beneficial to improving the corrosion potential of the grain boundary phase. The thought is considered to be the key point for improving the corrosion resistance of the 7-series aluminum alloy, and is not seen in literature reports, which is the first innovation point of the invention.

At present, how to control the element content in the grain boundary phase of the 7 series aluminum alloy is basically based on experience, and the national research on alloy elements (such as research on the diffusion of the alloy elements) is represented by Duyong professor of the university of China and south and the team thereof (see documents: Y. Du, Y. Chang, B. Huang, W. Gong, Z. Jin, H. Xu, Z. Yuan, Y. Liu, Y. He, F.Y. Xie, mater. Sci. Eng., A363 (2003) 140). Deep explanation for corrosion performance theoretically lacks a mature theory. The difficulty is to control the distribution of a specific element only in the grain boundary or only in the interior of the grain based on precise calculation of thermodynamics. This requires a profound understanding of the laws of atomic migration and thermodynamic properties of aluminum alloys in order to make the most of the changes in external conditions (e.g., temperature, time, process) to facilitate the diffusion of these elements as desired. Our studies show that: under certain conditions, Mg and Zn elements in the Al alloy can be distributed only in the interior of grains and not in a grain boundary phase. The distribution characteristic improves the electrode potential of the grain boundary phase, so that the corrosion primary cell reaction between crystal grains and the grain boundary phase is inhibited. As shown in the attached figure 1, the content of Mg and Zn in grain boundary positions is controlled by the invention, and compared with the grain boundary positions of a comparative alloy, segregation of Mg and Zn elements is not observed in the embodiment of the invention. It is this distribution of elements that improves the corrosion resistance of the alloy, which is the second innovation of the present invention.

Disclosure of Invention

In order to improve the corrosion resistance of high-zinc and low-copper aluminum alloy, the invention provides an alloy containing Mg, Zn, Cu, Cr and Y. The content of the elements is represented as follows: higher Zn content, about 11 wt.%; lower Cu content, about 1 wt.%; higher Zn to Mg ratio, about 5.5, higher Y content, >1.4 wt.%. The specific components are that the content of each element is Zn =10-12wt.%, Mg =1.8-2.0wt.%, Cu =0.97-1.0wt.%, Cr =0.08-0.1wt.%, Y =1.4-2.0wt.%, and Al = the rest.

During smelting, the volatilization of Zn is required, most of alloy elements are preferably added in the form of intermediate alloy, and other refining and degassing processes are the same as those of the common aluminum alloy smelting process. After the alloy is cast into an ingot, carrying out the I-th solution heat treatment at the temperature of 460-480 ℃, wherein the time of the solution heat treatment is between 2 and 4 hours, so as to ensure that the alloy elements are dissolved into the aluminum as much as possible. Then, the alloy is subjected to the II heat treatment at the temperature of 110-125 ℃ for 20-26 hours, then is subjected to the III heat treatment within the range of 160-180 ℃ for 0.5-2 hours, and finally is subjected to the IV heat treatment at the temperature of 110-125 ℃ for 20-26 hours. And the room temperature cold water is adopted for cooling between each heat treatment.

The alloy has the remarkable characteristic that the corrosion resistance can be close to the level of pure Al in an environment with saturated NaCl solution as electrolyte (see attached figure 1). The hardness of the alloy is about 19 under the condition of large grains with the average size of about 30um5N/mm²The strength was about 630MPa (see FIG. 2B). In the invention, Y element and other elements have synergistic effect, and the corrosion resistance can be improved by 45% compared with the alloy with zero content of Y element (see figure 2A). Meanwhile, the corrosion condition of the alloy of the invention after being soaked in saturated NaCl for 30 days is observed, and the corrosion condition of the grain boundary phase is greatly inhibited (see figure 3).

Drawings

FIG. 1 shows the distribution of Mg, Zn, Cu elements in two aluminum alloys, wherein the lower part of the diagram is marked as (B) (G) (H) (I) (J) in the embodiment of the present invention. The Mg and Zn elements in the alloy of the invention are uniformly distributed in the alloy, while the Mg and Zn elements in the comparative aluminum alloy are more distributed in the grain boundary, as shown by red arrows.

FIG. 2 shows the surface of the alloy after 30 days of immersion in saturated NaCl solution. Where plot (a) is the alloy sample surface without Y added, plot (B) is the alloy surface with a Y content of 2.0wt.%, and plot (C) is the pure Al surface.

FIG. 3 shows the corrosion of grain boundary phases (white regions) of different alloys after 30 days of immersion in saturated NaCl solution, where (C) and (D) are examples of the present invention and (A) and (B) are comparative examples. The present invention greatly suppresses corrosion of the grain boundary phase, and compared with the corrosion products (black areas) in the graphs (a), (B), it can be seen that the grain boundary phase inside the alloy of the present invention is very complete, and no corrosion phenomenon is observed.

FIG. 4 shows the difference in corrosion resistance (A) and hardness of the alloy of the present invention relative to the comparative alloy. After 30 days of immersion in saturated NaCl solution, the weight of the corrosion products in the examples of the invention is reduced by about 45%, and their hardness is reduced by only about 10N/mm²。

Detailed Description

Example (b):

this embodiment is merely to illustrate the effects exhibited by the present invention. The smelting mode in the embodiment is a special small-batch smelting mode adopted in a laboratory, and the smelting is carried out under the protection of argon, so that the working procedures of degassing and the like in actual production are omitted. In actual production, smelting can be carried out according to the degassing refining mode of 7 series aluminum alloy, and the quality and the performance of the cast ingot, such as strength, plasticity, porosity and the like, can be further improved.

The ingredients are mixed according to the table I in percentage by weight. The metallic blocks of Al, Zn, Mg, Cr and Y have a purity of greater than 99.9 and a total weight of 20 g. In the material preparation process, in order to supplement Zn volatilization loss in smelting, the weight of Zn is excessive by 3 percent.

Table one example ingredient table.

Numbering	Zn(g)	Mg(g)	Cu(g)	Al-Cr(g,10%Cr)	Y(g)	Al(g)
							①	2.266	0.4330	0.34	0.14	0.0000	16.90
②	2.266	0.4326	0.34	0.14	0.2828	16.62
							③	2.266	0.4326	0.34	0.14	0.3434	16.52
④	2.266	0.4326	0.34	0.14	0.4040	16.50

All the metal elements were charged into an electric arc furnace of type DHL-400 produced by shenyang instruments. The electric arc furnace is vacuumized and filled with argon, and the operations are repeated for three times to realize the complete furnace washing effect. In order to avoid metal volatilization during metal melting, low current is firstly adopted for melting. After all the metal had melted, the sample was turned over and remelted 4 times to ensure homogeneity of the alloy.

And putting the smelted alloy block into an alumina crucible and placing the alumina crucible into a resistance furnace. The furnace was warmed to 720 ℃ and held for 90 minutes. And rapidly slagging off the alloy liquid after the alloy liquid is discharged out of the furnace, and then directly casting the molten alloy liquid into a mold. All the alloy ingots were processed into square bars of 5X 15 mm and then subjected to subsequent heat treatment.

The heat treatment is first solutionized at 470 ℃ for 3 hours and quenched by dropping into cold water. The alloy blocks were then aged at 110 ℃ for 24 hours, 170 ℃ for 1 hour, and then re-aged at 110 ℃ for 24 hours. And cooling the sample by adopting cold water after the aging treatment is finished. Corrosion experiments were performed by soaking directly in saturated NaCl solution for 30 days, then weighing after 3 hours of drying in a vacuum oven at 40 ℃, and the amount of corrosion products was reflected by the weight increase before and after soaking. Hardness was controlled using microhardometers with loading forces of 0.5g (HV 0.5) and 1.0g (HV 1) respectively, tested 5 times on each piece of equipment at different locations on the alloy. The results are shown in FIG. 4, where the corrosion resistance of the alloy of the invention is improved by about 45% and the hardness is reduced by only about 10N/mm, compared to the comparative alloy (Table one component No. 1)²。

Claims

1. A high-zinc low-copper aluminum alloy with excellent corrosion resistance is characterized in that: the metal material comprises the following elements in percentage by mass, Zn =10-12wt.%, Mg =1.8-2.0wt.%, Cu =0.97-1.0wt.%, Cr =0.08-0.1wt.%, Y =1.4-2.0wt.%, and Al = the balance.

2. A preparation method of high-zinc and low-copper aluminum alloy with excellent corrosion resistance sequentially comprises the following steps:

(1) sequentially smelting and casting raw materials corresponding to the corrosion-resistant aluminum alloy component of claim 1 to obtain an aluminum alloy casting blank;

(2) sequentially carrying out the first heat treatment, the second heat treatment, the third heat treatment and the fourth heat treatment on the aluminum alloy casting blank to obtain corrosion-resistant aluminum alloy;

the temperature of the I heat treatment is 460-480 ℃;

the temperature of the second heat treatment is 110-125 ℃;

the temperature of the third heat treatment is 160-180 ℃;

the temperature of the IV heat treatment is 110-125 ℃.

3. The method for preparing high-zinc low-copper aluminum alloy with excellent corrosion resistance as claimed in claim 2, wherein the heat treatment I is carried out for 2-4 hours;

when the second heat treatment is carried out, the heat preservation time is 20-26 hours;

when the heat treatment of the III is carried out, the heat preservation time is 0.5 to 2 hours;

and when the IV heat treatment is carried out, the heat preservation time is 20-26 hours.

4. The method for preparing high zinc, low copper aluminum alloy with excellent corrosion resistance as claimed in claim 2 or 3, wherein all the heat treated alloys are rapidly cooled in cold water at room temperature after being taken out of the furnace.