Influence of two-step aging on structure and stress corrosion sensitivity of friction stir welded 7050-T7451 aluminum alloys
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摘要: 采用搅拌摩擦焊方法对3 mm厚7050-T7451铝合金进行焊接,为改善接头应力腐蚀敏感性,焊后进行121 ℃ × 5 h + 163 ℃ × 27 h双级时效处理. 通过对微观组织、显微硬度以及应力腐蚀敏感性的分析,研究双级时效对焊接接头性能的影响. 结果表明,双级时效后晶粒发生粗化,晶界内析出相和周边无沉淀析出带(PFZ)变宽,导致在热影响区和热力影响区出现大量不连续晶界;接头热影响区的显微硬度有所下降,但范围明显变窄,接头组织的均一性得到改善;时效处理后的接头在进行应力腐蚀试验 60天后仍未发生断裂,而未经时效处理的接头在1天内全部发生断裂,说明双级时效有效降低了焊接接头的应力腐蚀敏感性.Abstract: 3 mm thick 7050-T7451aluminum alloy joint was obtained by friction stir welding, and the two-stage aging treatment was performed at 121 ℃ × 5 h + 163 ℃ × 27 h after welding. Microstructure, hardness profiles and stress corrosion sensitivity of the joint were measured and studied. The results indicate that through the two-step aging, the grain size is coarsened, the age-hardening precipitates and PFZ become wider at the same time, which results in the discontinuous grain boundary; the microhardness of the FSW joints decreased, but the heat-affected zone significantly narrowed, which increased the uniformity of the microhardness of the FSW joints; and the two-stage aging effectively reduced the stress corrosion sensitivity of the FSW joints. The joints with aging treatment were not broken after 60 days, however all the joints without aging treatment were broken within 1 day.
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图 2 AA7050 焊接接头时效处理前后组织形貌
Figure 2. Organization morphologies before and after aging treatment of AA7075 welding joint. (a) before aging treatment welding nugget zone; (b) after aging treatment welding nugget zone; (c) before aging treatment thermal-mechanical affect zone; (d) after aging treatment thermal-mechanical affect zone; (e) before aging treatment heat affected zone; (f) after aging treatment heat affected zone
表 1 7050-T7451铝合金化学成分(质量分数,%)
Table 1 Chemical compositions of 7050-T7451 Al alloy
Zn Mg Cu Fe Si Zr Mn Ti Cr V Al 6.1 2.2 2.1 0.09 0.06 0.09 0.01 0.04 0.01 0.01 余量 表 2 7050-T7451铝合金力学性能
Table 2 Mechanical properties of 7050-T7451 Al alloy
抗拉强度Rm/MPa 屈服强度Rp0.2/MPa 断后伸长率A(%) 534.5 472 12.8 -
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