焊接能量对Mg/Al超声波焊接接头微观组织与力学性能的影响

Effect of Welding Energy on Microstructure and Mechanical Properties of Mg/Al Joints Welded by Ultrasonic Spot Welding

在Mg/Al超声波焊接(USW)领域,现有研究侧重于接头的组织性能,但对焊接过程中的界面应力分布和成形机制报道较少。运用USW技术制备了Mg/Al异种金属搭接接头,通过FEA、OM、SEM、EDS、XRD及剪切试验等测试手段,研究不同焊接能量对接头的界面应力分布、界面峰值温度、界面连接状态、微观组织特点以及力学性能的影响规律。研究发现:焊接过程中Mg/Al界面应力分布较均匀,连接界面较平直,未出现明显的漩涡状塑性流动和机械咬合。随着焊接能量的增加,界面应力水平提高,峰值温度升高,界面冶金结合区域逐渐增大。以有限元仿真模拟为基础,系统地分析阐述界面成形机制,指导选择合适的热输入量,以期为Mg/Al超声波焊接在实际生产应用中提供必要的技术和数据支撑。当焊接能量为500 J时,界面处生成Al_(12)Mg_(17)金属间化合物(IMC),而且随着焊接能量的增加,IMC层增厚,导致接头剪切性能随着焊接能量的增加呈现出先增加后减小的趋势,厚度适中的IMC层对提高接头力学强度具有重要意义。

Existing studies focus on the microstructure and mechanical properties of joints,but there are few reports on the interfacial stress distribution and forming mechanism during welding process in the field of Mg/Al ultrasonic spot welding(USW).Mg/Al dissimilar metal lap joints are prepared by USW technology.The effects of different welding energies on the interfacial stress distribution,interfacial peak temperature,interfacial connection state,microstructure characteristics and mechanical properties of joints are investigated by means of FEA,OM,SEM,EDS,XRD and shear tests.It is shown that the Mg/Al interfacial stress distribution is uniform during the welding process,and the connected interface is relatively straight with no obvious whirlpool-like plastic flow and mechanical occlusion.The interfacial stress level and the peak temperature increase with the increase of welding energy,resulting in the metallurgical bonding area at the interface gradually increases.Based on the finite element simulation,the interface forming mechanism is systematically analyzed to guide the selection of appropriate heat input,in order to provide the necessary technical and data support for the actual production application of Mg/Al ultrasonic spot welding.When the welding energy is 500 J,the Al12 Mg17 intermetallic compound(IMC)is formed at the interface and the intermetallic compound layer gradually thickens as the welding energy increasing,leading to the shearing force of joints increase first,reach to a peak value and then decrease with the further increase of welding energy.The moderate thickness of the IMC layer plays an important role in improving the mechanical strength of the joint.