超声振动强化搅拌摩擦焊的热力行为及微观组织特征

为了利用超声振动降低搅拌摩擦焊过程中金属材料的屈服应力和流动应力，研发超声振动强化搅拌摩擦焊试验装置，开展6061-T6铝合金的焊接工艺试验。采用实时采集焊机电参数并将其转化成力矩和力的方法，测试超声振动作用下搅拌摩擦焊的焊接载荷，利用热电偶测试施加超声时的焊接热循环，通过体视显微镜和金相显微镜分别观测焊缝截面尺寸和接头微观组织，并与相同参数下常规搅拌摩擦焊的情况进行比对。研究结果表明，超声振动能够显著降低焊接轴向压力和搅拌头转矩，增大焊缝横截面尺寸，细化和均匀焊核区和热力影响区的晶粒组织。热循环的测量结果显示，超声振动的施加略微降低了测量点的焊接热循环峰值温度。分析认为，超声振动与搅拌头附近的塑性变形材料相互作用，降低了金属材料的屈服应力和流变应力，进而改变了原有的温度场，从而产生了优异的工艺效果。

Thermo-mechanical Behaviors and Microstructure Characteristics of Ultrasonic Vibration Enhanced Friction Stir Welding

In order to utilize the ultrasonic energy to reduce the yield stress and flow stress of the metal materials during friction stir welding(FSW), the experimental system of the ultrasonic vibration enhanced friction stir welding(UVeFSW) is developed, and tests are conducted with 6061Al-T6 alloy plates. The welding load under the ultrasonic vibration are measured by real-time capturing the electrical parameters of the FSW machine and translating them to torque and force according to specific formula. Thermal cycle is measured by embedding thermal couples in specific positions. Weld cross-section size and microstructure in UVeFSW are also observed by stereomicroscope and metalloscope. They are all compared with those in conventional FSW at the same welding parameters. The results reveal that the ultrasonic vibration reduces the axial force and tool torque significantly, enlarges the weld cross-section size, refines and homogenizes the grains in weld nugget and thermo-mechanically affected zone. The measurements of the thermal cycle shows that the peak temperature of the measured points slightly decrease under ultrasonic vibration. It is inferred that the exerted ultrasonic vibration interacts with the plasticized material near the tool, decreases the yield stress and flow stress of the metals, and changes the temperature field, so that statisfactory results are achieved.