锌夹层添加对镁-铝异种金属搅拌摩擦点焊接头组织与性能的影响

Influence of Zn Interlayer Addition on Microstructure and Mechanical Properties of Friction Stir Spot Welded Mg-Al Dissimilar Joints

对于镁-铝异种金属的搅拌摩擦点焊(Friction stir spot weld,FSSW),镁-铝界面处连续分布的脆性Mg-Al金属间化合物是影响其强度的关键因素。针对AZ31镁合金和2024铝合金薄板的FSSW,采用0.1 mm厚纯锌箔作为预置夹层,分析锌夹层添加对接头微观组织与力学性能的影响。结果表明,无夹层时,接头中仅在钩状区中的镁-铝界面处生成了厚度约为5μm的连续金属间化合物层,其余部分以机械结合为主,接头拉剪载荷仅为0.8 k N。锌夹层添加后,降低了钩状区中靠近匙孔一侧的过渡层厚度(约2μm),并使钩状区外侧界面处生成了新型Al-Zn、Zn-Mg化合物组织,起到了阻碍该区域Mg-Al金属间化合物生成的作用,达到了促进镁、铝之间冶金结合的效果。与无夹层相比,有夹层接头拉剪载荷提高了75%,达到1.4 k N。

For the friction stir spot welding （FSSW） of Mg-A1 dissimilar metals, the joint strength is deteriorated due to the formation of intermetallic compound （IMC） layer at the interface. In the present study, AZ31 Mg and 2024 A1 sheets are friction stir spot welded with and without the addition of a Zn interlayer 0.1 mm in thickness. The results show that the load of the Mg-A1 FSSW joint without the Zn interlayer is only 0.8 kN due to the mechanical bonding between Mg and AI substrates as well as the formation of 5 μm thick IMC layer at the interface. For the joints with Zn interlayer, for the region away from the keyhole in the hook region, the Zn interlayer reacts with the substrates, forming the AI-Zn zone and Zn-Mg zone, thereby eliminating the formation of Mg-AI IMCs. In addition, the Zn interlayer reacts with the substrates, reducing the IMC layer thickness to about 2μm next to the keyhole in the hook region. As a result, the joint load increases from 0.8 kN to 1.4 kN with a increase of 75%.