AZ31B镁合金超声强化TLP接头组织演变及缺陷分析

超声强化瞬间液相扩散焊(U-TLP)可在大气环境下实现难润湿材料的快速连接，是一种高质量、高效率、低成本的先进连接方法. 文中以AZ31B 镁合金为基材，纯Zn为中间层，分析超声作用下结合区组织演变规律，探究AZ31B镁合金U-TLP接头缺陷形成机理. 结果表明，随着超声时间的延长，结合区组织由细小的Mg-Zn共晶相及MgZn，Mg7Zn3相组成的共晶花纹组织逐渐向扩散完全的α-Mg 固溶体转变，接头压剪强度随之提高. 但随超声时间的延长，结合区产生孔洞缺陷的几率增加，当超声时间增加至60 s时，孔洞缺陷占焊缝总长度的46.4%，接头压剪强度为55 MPa，为母材压剪强度的64.7%. 采用在冷却过程中二次超声强化工艺可有效提高原子扩散程度，接头压剪强度同比提高17%.

Microstructure evolution and defect analysis of ultrasonic-assisted transient liquid phase bonding of AZ31B Mg alloy

Ultrasound-promoted transient liquid phase bonding (U-TLP) can achieve fast connection of difficult-to-wet materials in the atmosphere. It is a high-quality, high-efficiency, low-cost advanced connection method. This paper uses AZ31B magnesium alloy as the substrate. Pure zinc is the middle layer, and the evolution law of the microstructure of the bonding zone under ultrasonic irradiation is analyzed. The formation mechanism of Mg/Zn/Mg U-TLP interface defects is investigated. The results show that the microstructure of the bonded zone is composed of fine Mg-Zn eutectic with the extension of ultrasonic time. The liquid phase structure consisting of alternating MgZn and Mg7Zn3 phases gradually transforms to the fully diffused α-Mg phase, and the joint shear strength increases. However, when the ultrasonic time is increased to 60s, due to the loss of the liquid phase, pore defects appeared along welding seam. The joint shear strength is 55 MPa, which is 64.7% of the base material compressive shear strength. Using the secondary ultrasonic optimization process during the cooling process, the joint shear strength increased by 17%.