镁合金/镀锌钢板电阻点焊接头拉剪断裂分析

Analysis of joint fracture of magnesium alloy and galvanized steel by resistance spot welding

针对2.0 mm厚的AZ31B镁合金以及1.0 mm厚的SPHC镀锌钢板,采用kDWJ-17型三相次级整流电阻焊机进行焊接试验,通过对接头的金相观察、扫描电镜分析,结合原子结合能研究点焊接头拉剪断裂特征.结果表明,点焊接头断裂的形式呈现结合面断裂和纽扣断裂两种方式,纽扣断裂抗拉剪力学性能优于结合面断裂,纽扣断裂断口是以韧性断口为主,脆性断裂为辅的混合断口.熔核区以Fe-Al化合物为主时发生纽扣断裂,熔合线边缘晶粒尺寸粗大以及熔核区Fe-Al化合物结合能大,使其断裂位置在熔合线边缘.熔核区以Mg-Zn化合物为主时发生结合面断裂,其Mg-Zn化合物结合能偏小,容易被拉断.

2. 0 mm thick AZ31 B magnesium alloy and 1.0 mm thick SPHC galvanized steel were welded by kDWJ-17 three-phase secondary rectification resistance welding machine.The fracture feature of the joint of magnesium alloy and galvanized steel by resistance spot welding was studied by the optical microscopy observation,scanning electron microscopy( SEM)and atomic binding energy. The results show that: joint fracture presented in the form of junction surface fracture and button fracture. Tensile shear of button fracture was better than junction surface rupture. Button fracture was main of ductile fracture surface,mixed little brittle fracture surface. Button fracture occured when Fe-Al compound is mainly distributed in the nugget. Grain growed coarse near the fusion line and Fe-Al binding energy is strong made the fracture location were in the fusion line. Joint surface fracture occured when Mg-Zn compound was main in the nugget. Binding energy of Mg-Zn compound is weak,which were easily pulled off.