利用直流脉冲MIG焊接技术，进行6061变形铝合金与A356铸造铝合金板材的搭接焊接，并分析接头的力学性能、微观组织及元素分布。拉伸试验结果表明，当A356铸造铝合金板在上，6061变形铝合金板在下，焊枪行走速度为10 mm/s时，搭接接头抗拉强度最高，为95 MPa。接头拉伸试样的断裂位置都位于焊缝区，断裂形式主要为混合型断裂。微观组织及元素分析结果表明，在A356铝合金一侧的部分熔融区内发生Fe和Mg元素偏聚，形成了片状Al-Fe-Si相和颗粒状Al-Fe-Mg-Si相，这两种富Fe相会削弱接头性能。在6061铝合金一侧的部分熔融区内产生了晶界液化，形成了Al-Mg-Si-Cu相+Al固溶体贫化区的液化组织，且该相周围有Fe元素偏聚。三角区是接头中最薄弱的位置，接头拉伸试样均起裂于此并最终断裂于焊缝。

Lap joining between wrought 6061-T6 and cast A356-T6 aluminum alloys plates by direct current pulse MIG welding is investigated. The mechanical property,microstructure and composition of the joints are analyzed. The tensile results indicate that the maximum tensile strength of the joints is 95 MPa with the welding speed of 10mm/s and joint design with A356-T6 aluminum alloy as upper plate. The samples during tensile test fail mainly in weld through mixed fracture mode. The analysis on the microstructure and composition of the joints shows that the segregation of Fe and Mg occurs in the partially melted zone on A356 aluminum alloy side,resulting in formation of flake-like Al-Fe-Si phases and Al-Fe-Mg-Si particles,and these Fe-rich phases can weaken the joints. Grain boundary liquation occurs in the partially melted zone on 6061 aluminum alloy side,which is composed of Al-Mg-Si-Cu phases and solute-depleted α-Al zone,and a little Fe segregated near this structure. The weakest position locates at the root of the lap joint,where the tensile samples crack and finally fracture through the weld.