针对熔焊条件下液态镁和铝易反应生成脆性Mg-Al化合物进而恶化镁合金/铝合金接头性能的难题,提出了镁合金在上铝合金在下且添加Ni夹层的激光熔焊技术,并采用该技术对AZ31镁合金和6061铝合金进行了焊接;基于热力学性能和力学性质的计算选择夹层元素,并研究了Ni夹层对激光熔焊接头组织和剪切性能的影响。结果表明:在激光功率为1450 W、焊接速度为1200 mm/min、激光头偏转20°、离焦量为0 mm、采用氩气作为保护气体进行侧吹和背面保护的工艺条件下,添加Ni箔夹层的焊缝表面呈规则的鱼鳞状,焊缝表面均匀,焊缝成形良好,接头的剪切强度(线载荷) 最高,为78.92 N/mm;Ni箔夹层可以起到阻隔作用,限制下层铝合金熔体中的Al向上扩散进入上层的镁合金熔池中,减少Al、Mg反应生成脆性Mg-Al化合物的量;此外,接头熔池区域中的Ni、Al反应生成了延性化合物AlNi和Al3Ni,其结构稳定性优于Mg-Al化合物,可以降低接头的脆性。上述的协同作用是添加Ni夹层改善镁合金/铝合金焊接接头剪切性能的重要原因。

To address the deterioration of the joint performance owing to the formation of brittle Mg-Al compounds, this paper proposes a laser fusion welding technology by adding Ni interlayer to magnesium and aluminum alloys'' interface layer. A lap joint is applied with a magnesium alloy sheet on the top and an aluminum alloy sheet at the bottom. The interlayer element is selected based on the calculations of thermodynamic properties and mechanical properties calculations. Finally, the effects of Ni interlayer on the microstructure and properties of fusion welded joints are studied. Results show that the surface of the joint with an Ni interlayer exhibits a regular fish scale, the weld has good formability, and the maximum shear strength (linear load) of the joint is 78.92 N/mm under laser power of 1450 W, a welding speed of 1200 mm/min, a laser head deflection angle of 20°, a defocus amount of 0 mm, and side blowing and back protection using the Ar protective gas. The Ni interlayer foil acts as a barrier to limit the upward diffusion of the Al element in the lower aluminum alloy liquid into the upper magnesium alloy molten pool; therefore, the formation of brittle Mg-Al compounds is reduced. In addition, the reaction of Ni and Al in the molten pool region of alloys joint to form ductile AlNi and Al3Ni compounds, AlNi and Al3Ni compounds have better ductility, and their structures are more stable than those of Mg-Al compounds, implying that the joint brittleness is reduced. The above synergistic effect is an important reason why adding Ni interlayer improves the shear performance of welded joints of magnesium/aluminum alloys.