焊后热处理对异种金属搅拌摩擦焊2024-T4和7075-T6铝合金接头性能的影响

摘要

The effect of post-weld heat treatment on dissimilar friction stir welded AA7075 and AA2024 joints was studied. After welding in constant parameters, solution heat treatment and various aging treatments were given to the welded joints. Microstructural and phase characterizations were done using optical microscope, SEM, FE-SEM, XRD and EDS techniques. Finally, mechanical properties of post-weld heat treated joints were evaluated and compared with as-welded joints. Results show that both 2024-T6 and 7075-T6 post-weld heat treatment procedures considerably improve the mechanical strength of the welded joint, with higher strength obtained for the 7075-T6 procedure, in comparison with the as-welded joint. This is explained by the formation of fine precipitates during the aging process, despite the abnormal grain growth. Fracture occurs at the interface between thermo- mechanical affected zone (TMAZ) and heat affected zone (HAZ) on the retreating side (AA7075) of as-welded joint, while by applying post-weld heat treatment fracture location shifts towards the stir zone (SZ) of the welded joint. Also, for post-weld heat treated samples, fracture surface is predominantly inter-granular, while in as-weld joint, fracture surface is mostly trans-granular. This is explained by dissolution and coarsening of precipitates within grains in post-weld heat treated joints.%研究焊后热处理对异种金属搅拌摩擦焊AA7075和AA2024接头性能的影响.在一定的参数下焊接后,对焊接接头进行固溶处理和不同的时效处理.采用光学显微镜、SEM、FE-SEM、XRD和EDS表征材料的显微组织和相成分,最后测试对比热处理前后样品的力学性能.结果显示,与焊接后未热处理的接头相比,焊后热处理过程可以明显提高2024-T6和7075-T6焊接接头的力学性能,7075-T6的力学性能提高更明显,这是因为在时效过程中形成细小沉淀相,尽管有异常晶粒长大.未热处理的AA7075的接头断裂发生在后退侧热机械影响区(TMAZ)和高热影响区(HAZ)的界面,而热处理后断裂位置转移到接头的搅拌区(SZ).未热处理的接头断裂为穿晶断裂,而热处理后样品的断裂主要以晶内断裂为主,这主要是因为接头热处理后晶体内的沉淀相发生分解和粗化.