Experiments of TIG welding-brazing of AZ31B magnesium alloy and PRO500 steel were carried out to investigate the effect of heat input on the microstructure and mechanical properties of lap joints.The results indicated that a effective bonding achieved between AZ31B magnesium alloy and PRO500 steel by TIG welding-brazing method.Under a optimized current process parameters,the strength of the joint could reach 85 ％ of the Mg alloy base metal.The transition zone in the interface was formed including the formation of the Fe-Mg-O compounds,the AlFea intermetallic compound (IMC),and the cross diffusion of the elements Fe and Mg from the substrate.The fracture mode of AZ31B/PRO500 joint presented a mixed-rupture characteristics of quasi-cleavage and tearing at a smaller heat input.With the increase of welding current,the fracture mode changed to a brittle rupture with the leading role of the quasi-cleavage fracture.Then the bonding strength decreased obviously.%利用TIG电弧作为热源开展了AZ31B镁合金与超高强钢PRO500熔-钎连接试验,研究了不同焊接热输入条件对接头微观结构及力学性能的影响.结果表明:利用TIG电弧能够实现AZ31B镁合金/PRO500钢的有效熔-钎连接,强度可达镁合金母材的85％,接头界面区形成由Fe-Mg-O化合物、金属间化合物AlFe3相和基体Fe元素、熔敷金属中扩散过来的Mg元素等共同组成的过渡区;随着焊接电流的增大,AZ31B镁合金/PRO500钢熔-钎焊接头断裂模式由包含了延性断裂和准解理断裂的混合断裂模式转化为准解理断裂主导的脆性断裂模式,结合强度显著下降.
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