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Mg3Al2和Mg12Al17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Mg2Sn,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％.
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 rrkagnesium 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 interdiffusion 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.
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