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Al-8.0Zn-2.1Mg-2.3Cu ultra high strength aluminum alloy sheet ingot homogenization treatment and aging treatment of the three

Author: ChenXiaoFei
Tutor: ZhaoGang;TianNi
School: Northeastern University
Course: Materials Science
Keywords: High strength aluminum alloy Semi-continuous casting Homogenization Solution treatment Three aging treatment
CLC: TG29
Type: Master's thesis
Year: 2009
Downloads: 76
Quote: 1
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Abstract


Al-8.0Zn-2.1Mg-2.3Cu type of ultra-high-strength aluminum alloy aerospace industry is urgently needed strength lightweight structural materials. But our country in such ultra-high-strength aluminum alloy industrial production is only in its infancy, the production of slabs often not up to the international production of these alloys developed level of performance problems, we address the problem, mainly through mechanical properties, electrical conductivity and resistance to exfoliation corrosion measurement and optical microscopy, scanning electron microscopy and transmission electron microscopy and micro-structure observation spectrum analysis and other means of ordinary semi-continuous casting of the alloy ingot and electromagnetic semi-continuous casting ingot side cast structure and uniformity of treatment, and the general semi-continuous casting of 25mm thickness after rolling the hot rolled sheet stretching board solution treatment and aging treatment of the pre-conducted studies to develop the optimum Al-8.0Zn -2.1Mg-2.3Cu high strength aluminum alloy ingot homogenization heat treatment process, and ultimately aging foundation. The main results obtained are as follows: (1) Al-8.0Zn-2.1Mg-2.3Cu Φ170mm ordinary high strength aluminum alloy continuous casting ingot melting point in the large number of non-equilibrium solidification 475 ℃ and the formation of dendritic crystals network of crystal lamellar second phase contains AlZnMgCu four elements, there are still strip ingot Al 7 Cu 2 Fe phase crystalline phase. The homogenized ingot after 470 ℃ for 24h, the alloy of non-equilibrium solidification crystal content drastically reduced, they are also dissolved in the substrate into the S-phase (Al 2 CuMg). Homogenization heat treatment time is increased to 48h after, S-phase (Al 2 CuMg) levels have decreased, but can not disappear. (2) low-frequency electromagnetic semi-continuous casting can significantly refine the Al-8.0Zn-2.1Mg-2.3Cu ultra high strength aluminum alloy semi-continuous ingot organization, but also lamellar eutectic alloy and Al 7 < / sub> Cu 2 Fe phase content decreased. (3) 25mm thick Al-8.0Zn-2.1Mg-2.3Cu presence of high-strength aluminum alloy hot rolled low melting point melting point of 475 ℃ to 483 ℃ products and melting point of the S-phase (Al 2 CuMg). Solution treated at 470 ℃ within 3 hours of the product of a melting point of 475 ℃ was significantly reduced, but a melting point of 483 ℃ 470 ℃ S-phase solution process is not changed. Solution treatment at 470 ℃ for more than 3 hours without significance. (4) after 470 ℃ × 3h 25mm thick plate solution treatment temperature is higher for the three second-stage aging treatment, the second stage aging treatment temperature alloys that time is to determine the strength and exfoliation corrosion key factor; alloy sheet and by the first stage solution treatment 120 ℃ aging for 24 hours, the second stage in the range 175 ℃ -185 ℃ aging time, with the second stage aging time from 0.5h extended to 3h, the tensile strength is substantially decreased, But the second stage aging temperature is high, the intensity decreased faster; when from the first stage to the second stage and the second stage heating faster aging time is shorter at higher temperatures, the three alloy strength after aging treatment can slightly higher than the temperature of the second stage aging results; 0.5h first stage aging treatment temperature to 175 ℃ for 2h or 185 ℃, insulation 1.5h, can make the alloy strength and corrosion resistance to achieve a good match.

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