回归再时效对7050铝合金强度和断裂韧性的影响

Effects of retrogression and reaging on strength and fracture toughness of aluminum alloy 7050

采用光学显微镜、扫描电镜、透射电镜、常温拉伸及断裂韧性实验研究回归温度及回归时间对7050铝合金力学性能和断裂韧性的影响。结果表明:回归过程中,一部分GP区回溶进入基体,另一部分长大转变为η′相,同时η′相转变为η相,η相则不断粗化。随着回归时间的延长,合金的强度先下降至一谷值然后上升至一峰值再单调下降;再时效态合金强度先增大后减小,再时效态合金强度大于对应回归态合金强度。在190℃回归时,回归及再时效7050合金(RRA)的断裂韧性均随回归时间的延长而不断增大;然而,在170和150℃回归时,回归及再时效7050合金的断裂韧性先增大至一峰值然后下降至一谷值再增大。回归态合金的断裂韧性大于对应再时效态合金的断裂韧性。随着回归时间的延长,合金的断裂模式由沿晶断裂向穿晶韧窝断裂过渡。

The effects of retrogression and reaging（RRA） on the tensile property and fracture toughness of aluminum alloy 7050 were investigated by optical microscopy,scanning electron microscopy,transmission electron microscopy,tensile and toughness tests.The results show that during the retrogression treating,one part of GP zone dissolves into Al matrix and the other grows,and then transforms into η′ phase.At the same time,the η′ phase transforms into η phase constantly.And the η phase becomes coarse gradually.With the retrogression time elongating,the strength of the alloy falls to a valley value before increasing to a peak value,and then monotonically decreases.Meanwhile,the strength of the reaged alloys first increases and then decreases.The strength of the reaged alloys is larger than that of the retrogressed alloys.With the retrogression time elongating,the fracture toughness of alloy 7050 RRA retrogressed at 190 ℃ increases.However,the fracture toughness of alloy 7050 RRA retrogressed at 170 ℃ and 150 ℃ increases to a peak value before decreasing to a valley value and then increases.The fracture toughness of the retrogressed alloys is larger than that of the reaged alloys.With the retrogression time elongating,the main fracture mechanism changes from the intergranular fracture to transgranular fracture.