不同电流下AZ31镁合金交流钨极氩弧焊焊接接头的显微组织与力学性能

摘要

AZ31 magnesium alloy sheet with 7. 4 mm thickness were welded by AC-TIG welding under different welding current The microstructure and mechanical properties of welding joint of AZ31 magnesium alloy were studied by optical microscopy, scanning electron microscopies, energy spectrometer, X-ray diffractometer, tensile test machine and micro-hardness instrument The results showed that the microstructures of the weld zone were fine equiaxed orMg matrix and β-Al12Mg17 phase which precipitated on grain boundaries, and the heat-affected zone was overheated structure, the grains of seam and heat-affected zone coarsened with the increasing welding current The effect of welding current on mechanical properties of the welding joint was larger, the tensile strength of welding joint began to increase and then decrease with the increasing welding current With 190 A welding current, the tensile strength of joint was up to 88% of the base material, the fracture with mixed toughness and brittleness occurred in the heat-affected zone. The microhardness of the joint showed a W-shaped distribution, the hardness value of weld was higher than that of the base metal, and heat affected zone had a lowest value.%采用交流钨极氩弧焊在不同焊接电流下对7.4 mm厚AZ31镁合金板进行了焊接试验，用光学显微镜、扫描电镜、能谱仪、X射线衍射仪、拉伸试验机和显微硬度计等研究了焊接电流对焊接接头显微组织与力学性能的影响。结果表明：焊缝区组织为细小的等轴状α-Mg基体相和沿晶界析出的细小β-Al12Mg17相，热影响区为过热组织；随着焊接电流的增大，焊缝和热影响区的晶粒粗化；焊接电流对接头力学性能影响较大，随着焊接电流的增大，抗拉强度先升高后降低，焊接电流为190 A时，接头的抗拉强度可达到母材的88％，断裂均发生在热影响区，断口呈现韧脆混合断裂特征；接头显微硬度呈典型的W形分布，焊缝的硬度较母材的高，热影响区硬度最低。