7020铝合金搅拌摩擦焊接接头微观组织和力学性能

摘要

通过显微硬度测试、室温拉伸性能测试、金相观察、扫描观察和高角环形暗场透射电镜观察等手段研究7020合金搅拌摩擦焊接焊缝的微观组织和力学性能.结果表明:合金焊缝处硬度呈W型分布,热机械影响区/热影响区(TMAZ/HAZ)硬度最低.焊接接头的抗拉强度为352 MPa,屈服强度为223 MPa,伸长率为9.8%,焊接系数达86.9%.合金经90 ℃/8 h+135 ℃/16 h双级时效处理并焊接后,焊缝处的晶粒组织差异明显,各区域GP区和η'相发生溶解,并重新析出更加细小均匀的GPI区,其尺寸和密度均小于原始基材.%The microstructure and mechanical properties of friction stir welded 7020-T6 alloy were investigated by micro-hardness test, tensile mechanical properties test, metangraphic microscope, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the hardness distribution appears as the W-shaped profile in alloy weld zone and reaches to minimum in HMAZ/HAZ. The tensile strength, yield strength, elongation and welding coefficient of the welded joint are 352 MPa, 223 MPa, 9.8% and 86.9%, respectively. The grain structure shows significant difference in the welded zone. The fine and dispersive precipitates of CP zone and η' phase formed after artificial aging (90 ℃/8 h+135 ℃/16 h) in base metal are dissolved during the process of friction stir weld and re-precipitate later, but the size and density of precipitates in welded joint are much smaller than base metal.