化学镀锡层对镁铝异种金属超声波焊接的影响

为提高镁铝异种金属超声波焊接接头强度,预先在铝合金表面镀锡后进行镁铝异种金属超声波点焊,并对接头的微观组织和力学性能进行分析.研究表明:无镀锡层的镁铝超声波焊接接头界面出现了大量的Mg_3Al_2和Mg_(12)Al_(17)相,其接头的最大拉伸剪切强度为27.5 MPa;含镀锡层的铝镁超声波焊接结合区由镁锡反应扩散层、残余锡层和铝锡反应扩散层组成,其中,铝锡反应层是固溶体层,镁锡反应层主要是过饱和的固溶体基体及弥散析出的中间相Mg_2Sn,其接头的最大拉伸剪切强度为32.9 MPa.镀锡层的加入有效阻止了镁铝的相互扩散,抑制了硬脆的Mg-Al系金属间化合物的生成,提高了镁铝超声波焊接接头强度,与镁铝超声波焊接相比最大拉伸剪切强度提高了19.6%.

Effects of chemical plating Sn coating on the ultrasonic spot welding of Mg/Al dissimilar metals

Main problem of magnesium/aluminum joining is the formation of hard and brittle Mg-Al intermetallic compounds (IMCs) at the interface. To improve the strength of the welding joints, the aluminum alloy was firstly chemical plated with a Sn layer and then welded with the magnesium alloy using the ultrasonic spot welding(USW) method. After that, the microstructure and mechanical properties were analyzed. Result shows that lots of Mg₃Al₂ and Mg₁₂Al₁₇ phases were found on the interface of Mg/Al USW joint without Sn layer, and the maximum lap shear strength of the joint is 27.5 MPa. While a characteristic of a multilayer sandwich structure was found on the interface of Mg/Al USW joint with Sn layer, which includes the transition zone of Mg-Sn, the residual Sn interlayer, as well as the transition zone of Al-Sn. The transition zone of Al-Sn is mainly composed of a solid solution structure, while the Mg-Sn transition zone is consist of supersaturated solid solution Mg and Mg₂Sn IMCs after a rapid eutectic reaction, and the maximum lap shear strength of the joint is 27.5 MPa. Sn coating is found to inhibit the inter-diffusion between Mg and Al alloys, eliminate the formation of the brittle Mg-Al IMCs, thus resulting in an enhancement of 19.6% of the lap shear strength of the joint compared to that of the directly welded Mg/Al joints.