AZ31B镁合金点焊接头拉剪断裂特征

针对板厚2 mmAZ31B镁合金板材在DZ-3×100三相次级整流点焊机上进行焊接.通过对其焊接接头的拉剪试验、金相显微观察、断口SEM分析、XRD分析,研究了镁合金点焊接头拉剪断裂特征.结果表明,点焊接头拉剪断裂呈现拉剪撕裂和整核断裂两种断裂形式.熔核处断口为韧性-脆性混合型断裂,母材断口处呈现一典型的韧性断裂特征.熔核与母材的物相基本一致.母材焊后,晶界及晶面上析出硬而脆的Mg17Al12金属间化合物,且所占比例远远超过母材基体,熔核区域的断裂倾向增大,Mg17Al12金属间化合物在XRD图谱上衍射峰强.

Fracture feature of spot welding joint under tensile-shear for AZ31B magnesium alloy

For AZ31B magnesium alloy sheet of 2 mm thickness,spot welding was carried at a three-phase secondary rectification welding machine DZ-3×100.Fracture feature of spot welding joint was studied by the tensile shearing test,optical microscope,SEM,X-ray method.The result showed that fracture of spot welding joint showed two kinds of fracture morphology under tensile-shear loading,one is tearing fracture,the another is whole nugget fracture.The fracture surface was a ductile-brittle mixed mode in the nugget region,whereas in base metal region it was a typical ductile mode.The phase of base metal is basically same as nugget in the spot welding joint.However the hard and brittle Mg17Al12 intermetallic compound is precipitated from intracrystalline or crystalline grain boundary in base metal after being welded,where the proportion is far more than that of base metal.It shows that fracture tendency of nugget region is more serious than base metal,and the diffraction peak of Mg17Al12 is more intense in the XRD patterns.