镁合金/不锈钢钨极氩弧焊熔钎焊接头结合界面微观组织分析

以黄铜为中间层, 采用钨极氩弧焊对 AZ31B镁合金和304不锈钢进行搭接熔钎焊, 观察分析了接头结合界面处的显微组织, 并测定了元素分布。结果表明, 在交流电流70 A、气流量15 L/min、焊接速度1.5 mm/s的条件下, 实现了镁合金和不锈钢的搭接熔钎焊。结合界面由铺展区、缩裂区和氧化区3部分组成。在铺展区, 镁合金在不锈钢表面润湿铺展良好, 形成有效的连接, 结合力最强; 在缩裂区, 部分位置有收缩形成的缝隙, 削弱了界面结合力, 结合力低于铺展区; 在氧化区, 镁合金被氧化, 只与不锈钢的表面形成微弱的连接, 结合力最弱。添加黄铜夹层, 增强了镁合金在不锈钢表面的润湿铺展, 增加了铺展区的长度, 从而增加了界面结合力。

Analysis of Interface Microstructure of TIG Brazing Joint of Magnesium Alloy and Stainless Steel

The TIG brazing of lap-jointed AZ31B magnesium alloy and 304 stainless steel was conducted with brass as an interlayer. The microstructure of the joint interface was observed and analyzed. The distribution of elements was determined. Results showed that magnesium alloy was brazed with stainless steel by TIG welding under the conditions including alternating current of 70 A, gas flow of 15 L/min and welding speed of 1.5 mm/s. The bonding interface consisted of three parts, spreading, shrinkage and oxidation zones. In the spreading zone, magnesium alloy had better wet spreading on the surface of the stainless steel, forming an effective connection with the strongest bonding force. In the shrinkage zone, cracks formed due to shrinkage at some positions, resulting in the weakened interface bonding strength, lower than that in the spreading zone. In the oxidation zone, magnesium alloy was oxidized, resulting in a weak connection with the stainless steel surface due to the weakest bonding force. An addition of brass interlayer enhanced the wet spreading of the magnesium alloy on the stainless steel surface, which increased the length of the spreading zone, thereby increased the interface bonding strength.