AZ31镁合金板材点焊接头的力学性能与断裂特征

Mechanical Properties and Fracture Characteristics of Spot Welded Joints of AZ31 Alloy Sheet

用交流点焊机焊接了AZ31镁合金板材,测试了不同表面清理状态下点焊接头的力学性能,用光学显微镜和扫描电镜分析了接头的显微组织和拉伸断口形貌。结果表明:在其它参数不变的情况下,接头的拉剪强度随电极压力的增加先增大,后减小,中间有个峰值;焊接电流和焊接时间对接头断裂强度的影响规律与电极压力相似。表面清理状态对接头的质量有很大影响,焊前未经过清理的接头强度较低;焊前经机械打磨的接头总体焊接质量较好;焊前采用化学清理的接头,质量稳定,接头强度随焊接电流的增大而提高。焊缝组织由等轴晶和柱状晶构成,拉伸断口呈韧脆混合的断裂特征。

AZ31 alloy sheet was welded by AC electric resistance spot welding. The mechanical properties of the welded joints at different surface conditions were tested. The microstructure and fracture of the welded joints were investigatd using a microscope and SEM. The results show that the tensile strength of the joints increases to a maximum value with increasing electrode force, then decreases regularly. There is a peak value in the middle. The influence of welding current and welding time is the same as electrode force. The surface conditions has significant influence on the quality of the joints. Un-cleaned joints have the lowest strength. The mechanically grinding joints have higher welding quality. The chemically processed joints have the best welding quality, and the strength of the joints increases with rising current regularly. The microstructure of the joints consists of equiaxial and cylindrical grains. The tensile fracture has the characteristic of tough-brittle mixed fracture.