DINGSHEN SUPPLY HIGH QUALITY AL7075-T651 ALUMINIUM BAR 3-500mm, AL7075-T651 ALUMINIUM BAR 1-500mm
Aluminum is one of the most abundant elements in the crust, accounting for about 8.2wt% of the total crustal mass. Aluminum usually exists in the form of oxides because of its active atmosphere. In Al2O3, it is difficult to extract Al by electrolysis, so the development history of aluminium has not exceeded 200 years. In recognition of Mendeleev's outstanding contribution to chemistry, the Royal Society of England made an aluminium cup for Mendeleev at great expense. At present, with the rapid development of aerospace technology, aluminum alloy and its composite materials have been widely used in aerospace because of their high specific strength, good corrosion resistance and good formability. 7075 (Al-Zn-Mg-Cu) superhard aluminium alloy was used in aircraft in the late 1940s. After that, many aerospace materials with excellent properties were obtained by adding other kinds of alloying elements, changing the content of alloying elements and changing the heat treatment process. The addition of Ni to Al-Zn-Mg-Cu alloy by Beerschamp et al. has been studied. The results show that in addition to neutralizing iron to form Al9FeNi phase, the strengthening phase Al7Cu4Ni is formed with 0.25% Ni content in the alloy, which plays a precipitation hardening role in the aging process.
1. Al-Zn-Mg-Cu Aluminum Alloys
Al-Zn-Mg-Cu aluminium alloy is a kind of high strength aluminium alloy at present. Its strength ranges from 500 MPa to 700 MPa. With its excellent technological properties, it has become an important structural material in aerospace industry. It is developed on the basis of Al-Zn-Mg alloys. It belongs to heat-treated and strengthened aluminium alloy. Its yield ratio is high and specific strength is also high, but its plasticity is low, its corrosion resistance is worse than pure aluminium, and its fatigue strength is not high. Usually, the method of coating aluminium is used to improve its corrosion resistance. When the temperature is higher than 120 C, it will soften sharply, in which the solid solution will decompose and the dispersed phase will grow sharply. The main chemical constituents are: chemical constituents /%, not more than other impurities /%, not more than
2. Heat Treatment of Al-Zn-Mg-Cu Aluminum Alloys
Al-Zn-Mg-Cu superhard aluminium alloys are usually annealed, quenched and aged (solution and aging) to obtain higher mechanical properties. Solution treatment is to integrate alloy elements into the matrix sufficiently. If the solution temperature is too high, the alloy elements will dissolve sufficiently, but usually the grain size will be large. Solution temperature is too low, the alloy elements dissolve insufficiently, which affects the effect of solid solution. Al-Zn-Mg alloys are widely used as welding structural materials because of their low solid solution treatment temperature, small influence of cooling rate on strength and good aging hardening effect at room temperature. After quenching, the solid solution is retained at room temperature. The quenching effect mainly depends on the solubility of alloy elements, the way of dissolution and the cooling speed of quenching. However, after quenching, the plasticity of aluminium alloy decreases obviously, the internal stress is higher and the cracking tendency is larger. Therefore, isothermal quenching is usually used to reduce this kind of problem. Moreover, the ability of solution strengthening is limited, so quenched aluminium alloys do not have the same high strength as steel. In the subsequent process, aging treatment plays an important role in strengthening of aluminium alloy. Aging is a process in which the second phase of quenched aluminium alloy precipitates in supersaturated solid solution after holding for a period of time at low temperature, resulting in changes in strength and hardness. According to the different aging temperature, it can be divided into low temperature aging (natural aging) and high temperature aging (artificial aging). In the aging process, it is very important to control the appropriate aging temperature and time. Deformed aluminium alloys are quite sensitive to aging. The heat treatment state of aluminium alloy can be subdivided into T1~T10. State Code Interpretation T1 High Temperature Forming+Natural Aging T2 High Temperature Forming+Cold Processing+Natural Aging T3 Solid Solution Treatment+Natural Aging T4 Solid Solution Treatment+Natural Aging T5 High Temperature Forming+Artificial Aging T6 Solid Solution Treatment+Artificial Aging T7 Solid Solution Treatment+Aging T8 Solid Solution Treatment+Cold Processing+Artificial Aging T9 Solid Solution Treatment+Artificial Aging+Cold Processing T10 High Temperature Forming+ Artificial aging
3. Strengthening mechanism of Al-Zn-Mg-Cu system aluminium alloy
There are many trace alloying elements in Al-Zn-Mg-Cu series aluminium alloys. The role of Zn, Mg and Cu in 7075 is discussed in this paper. The main strengthening elements in Al-Zn-Mg-Cu alloys are Zn and Mg. With the increase of the content of Zn and Mg, the strength of the alloys increases remarkably. They can form T (Al2Mg3Zn3) phase and_ (MgZn2) phase. The desolution and precipitation effect of these two phases is quite remarkable, which is the main strengthening means of 7075 series aluminum alloys. Cu also has certain strengthening effect, and S (Al2CuMg) phase can be formed by the combination of Cu and Al and Mg. To strengthen, the strength of the alloy can be improved. Its main function is to improve the corrosion resistance and the corrosion potential of the matrix. Many researchers at home and abroad have done a lot of research in this area. Liang Weisheng et al. analyzed the mechanical properties of Al-8.25Zn-2.4Mg-2.3Cu alloy by adding trace Zr and Er. It was found that the addition of Zr and Er could refine the structure of the ingot, mainly the core of crystallization nucleation during solidification. Moreover, its tensile strength and elongation have been significantly improved. Wei et al. added Li in Al-Zn-Mg-Cu system. The results showed that 1% Li could promote the dissolution of precipitated phase. The addition of Ni alloy elements to Al-Z n-M g-C u-R E super-high strength aluminium alloys by Biesqiang et al. The results show that the hardness can reach 138 HB and the precipitation of Al 7Cu4Ni can also be formed after 0.25wt% Ni is added.
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