7075-T6合金超声辅助搅拌摩擦焊接头搅拌区组织与力学性能

搅拌区的金属流动不充分容易导致轴肩影响区与搅拌针影响区之间的过渡区出现疏松缺陷并恶化接头的力学性能.在不同焊接参数条件下，对7075-T6铝合金分别进行常规搅拌摩擦焊接(FSW)和超声辅助搅拌摩擦焊接(UAFSW)，研究了超声振动对接头搅拌区的金属流动行为、微观组织特征和力学性能的影响.结果表明:相同焊接参数下，UAFSW接头搅拌区的力学性能均优于FSW接头.焊接参数为1000r/min-110mm/min 的UAFSW接头搅拌区的抗拉强度和延伸率最高，分别达到515MPa和17.3%.在搅拌摩擦焊接过程中施加轴向超声振动可以显著降低搅拌区金属的屈服应力和流变应力，促进塑化金属沿板厚方向的流动.消除搅拌区中过渡区的疏松缺陷，并细化微观组织，是接头力学性能提高的主要原因.

Microstructure and Mechanical Properties of the Stirred Zone of Ultrasonic Assisted Friction Stir Welded Joint of 7075-T6 Alloy

Insufficient metal flow in the stirred zone(SZ) may easily lead to loose defects in the transition zone between the shoulder-affected zone and the pin-affected zone， and deteriorate the mechanical properties of the joint. 7075-T6 aluminum alloy was subjected to conventional friction stir welding (FSW) and ultrasonic assisted friction stir welding (UAFSW) under different welding parameters， and the effects of ultrasonic vibration on the metal flow behavior， microstructure characteristics and mechanical properties of the SZ were investigated. The results show that the mechanical properties of the SZ of UAFSW joints are better than that of FSW joints processed using the same welding parameters. Tensile strength and elongation of the SZ of UAFSW joint with the welding parameters of 1000r/min-110mm/min reach the maximum values， i.e. 515 MPa and 17.3%， respectively. The application of axial ultrasonic vibration during FSW can significantly reduce yield stress and flow stress of the metal in the SZ， promoting the flow of plasticized metal along the normal direction of the plate. Eliminating the loose defects in the transition zone of the SZ and refining the microstructure are the main reasons for improving the mechanical properties of the joint.