The effect of homogenization and aging treatments on the strength and the stress-corrosioncracking (SCC) resistance of the 7050 aluminum alloy has been investigated and compared with those of the same-series 7075 alloy. The recrystallized structure and the quench sensitivity are found to be significantly affected by the dispersoid distribution, depending on the homogenization conditions. The finest and densest dispersoid distribution, generated by the stephomogenization (Step-H) treatment, can effectively inhibit recrystallization to obtain the smallest fraction of recrystallized structure. Such a characteristic lowers considerably the quench sensitivity of the 7050 alloy, but it produces the reverse in the 7075 alloy. For the 7050 alloy,Step-H always exhibits the highest strength among all the aging conditions, and the proposed step-quench and aging (SQA) treatment is confirmed to achieve an optimum strength and coarsened and wide-spaced grain-boundary precipitates (GBP), which have been found to improve the resistance of the SCC by the slow-strain-rate test (SSRT). Therefore, the attainment of both optimum strength and SCC resistance is possible for the 7050 alloy via the Step-H and SQA treatment. However, such treatment is not applicable to the 7075 alloy because of its inborn high quench sensitivity.
The influence of matrix and grain boundary microstructural characteristics on the mechanical properties and resistance to stress corrosion cracking (SCC) of the 7050 aluminum alloy was investigated. The proposed step‐quench and aging (SQA) treatment can effectively improve the SCC resistance and attain optimum strength by controlling the microstructures, i.e., the coarse and widely‐spaced grain boundary precipitates (GBPs), and a matrix of GP zones with η′ phases. The highest strength of the 7050 alloy is obtained by using duplex aging at 120°C for 6 h and then 168°C for 3 h in the T6 temper. When the duplex aging is used in the SQA treatment, not only the SCC resistance and yield strength are significantly improved, but also the aging time is much reduced simultaneously, as compared to those obtained by the conventional T73 treatment. The process has good potential to be applied in industry. However, the SQA treatment is not applicable to the 7075 alloy because of its high quench sensitivity.
This investigation studies 3003 aluminum alloys for automobile heat exchangers. The effects of precipitation in homogenization treatments, recrystallization in extrusion and brazing on extrusion forming ability and final material properties are examined. At first, fine second phase particles were precipitated during the 460 C Â 9 h homogenization treatment and coarse particles were precipitated by homogenization treatments with 600 C Â 9 h. Second, when the precipitation were not plentiful and fine enough during extrusion, the amount of solution dominated the extrusion breakout pressure, and recrystallization was easier; on the contrary, the domination state was replaced by plentiful and fine precipitated particles, and recrystallization became more difficult. Additionally, the hardness after extrusion was lower in the complete recrystallization position, and higher in the incomplete recrystallization position. Finally, in brazing, the sample under the 460 C Â 9 h condition (a) underwent full recrystallization from partial recrystallization with a reduction in strength; the local position of the edge of the sample under the 600 C Â 9 h ! 460 C Â 3 h condition (c) exhibited a second recrystallization and a significant drop in hardness.
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