镁/钢无匙孔搅拌摩擦点焊接头连接机理与断裂方式研究

Study on Connection Mechanism and Fracture Mode of Mg/Steel Keyholeless Friction Stir Spot Welding

采用最新研制的无匙孔搅拌摩擦点焊设备对AZ31B镁合金和DP600镀锌钢板进行搭接点焊试验。通过对点焊接头宏观、微观组织形貌及断口分析表明,接头搅拌区结合界面处镁钢呈“楔状”与“弯钩状”相互嵌入对方基体中,形成牢固的机械互锁结构,而轴肩作用区结合界面平整,生成了厚度约6～9μm的“竹节状”中间层,其长度各不相同,且中间层之间存在裂纹;点焊接头拉伸断口有两种断裂方式,轴肩作用区为解理断裂,搅拌区为韧脆混合断裂;原位拉伸试验结果表明,应力集中最大的部位在镁钢两板之间点焊接头的焊点边缘处;接头的拉伸断裂面靠近镁侧,断裂时脆性中间层基本上留在了钢侧。

The lap welding tests between AZ31 magnesium alloy and DP600 galvanized steel sheets were carried out by using newly developed keyholeless friction stir spot welding device. The analysis of the macrostructure, microstructure and fracture shows that the Mg alloy and steel are hooked into each other as wedge and hook at the bonding interface of stirring zone of the joint, and it forms strong mechanical interlock structure. However, the bonding interface of the shoulder zone is smooth and there exists about 6-9 μm thick bamboo interlayers with different lengths, and there is crack between the layers. There are two fracture modes in tensile fracture of the spot welded joint, one mode is cleavage fracture in the shoulder zone, another is ductile brittle fracture in the stirring zone. The in-situ tensile test results show that the maximum stress concentration position is located at the edge of the joint between magnesium and steel plates. The tensile fracture surface of the joint is close to the Mg alloy side and the brittle intermediate layer essentially remains on the steel side.