焊接电流对镁/镀锌钢 TIG熔--钎焊接头显微组织与力学性能的影响

采用TIG熔-钎焊焊接方法，以镁合金焊丝为填充材料，对镁合金与镀锌钢进行连接实验，并分析热输入量对接头显微组织和力学性能的影响.热输入量过小会阻碍镁/钢界面反应层的形成而使得焊缝难以焊合，热输入量过大又会促进焊缝内部脆性第二相的长大，降低接头力学性能.接头强度随着焊接电流和焊接速度的增大都呈现先上升后下降的趋势，电流为70 A时强度达到最大，该值接近AZ31B母材的88．7%.此时断裂发生于焊缝熔焊区，断面出现大量韧窝和撕裂棱，呈现出塑性断裂特征.

Effect of heat input on the microstructure and mechanical properties of TIG welded--brazed magnesium/steel joints

A tungsten inert gas ( TIG) welding-brazing technology using an Mg-based filler was developed for joining Mg alloys to steel. The effects of heat input on the microstructure and mechanical properties of Mg/steel joints were investigated. The results indi-cate that the joining strength of the joints is poor with low heat input, owing to insufficient metallurgical reaction between the Mg alloy and steel. But with excessive heat input, the growth of the brittle second phase in the seam occurs, resulting in the decrease of me-chanical properties. The joining strength of the joints increases first and then decreases with the increase of welding current and weld-ing speed. An acceptable joint is obtained with a welding current of 70 A, representing 88. 7% joint efficiency relative to AZ31B base material. With this parameter, fracture occurs at the fusion zone and the fracture surface is characterized by equiaxed dimple patterns accompanied with lamellar tearing. The fracture surface embodies the characteristics of plastic fracture.