| Magnesium and aluminum alloy have got more and more applications in light industry, and the welding problem between them is one of the key problems restricting its widespread applications. The surface of magnesium and aluminum alloy forms oxide film easily, and in the weld also easily form a large number of brittle inter metallic compounds. Friction stir spot welding(FSSW) with its inherent advantages becomes the preferred technology in the welding of Al/Mg alloy, and joining cementing technology on the basis of FSSW under certain conditions can get plastic welding head with enough strength and sealing performance, This bonding-Friction stir spot hybrid welding(Bonding-FSSW) composite connection technology has showed a new way for magnesium and aluminum alloy welding.In this paper, aiming at the two materials of AZ31Mg and5052Al alloy, first conduct material selection and design of the pin tool. Study found that shorting the length of the pin properly can obtain a joint with a good forming and properties. Then with the good pin tool do FSSW of Al/Mg alloy test, analyzing the influence of different process parameters (rotational speed, shoulder press and welding time) to the joint. Results show that the rotational speed:800-1200r/min, press quantity:0.25-0.35mm,welding time:4～8s, in this range can get a better welding spot, the shear resistance is between2and4KN. Finaly analyzing the microstructure and performance to the joint, the analysis shows that in the border of Al/Mg formed a diffusion layer composed of magnesium alloy, Transverse fracture surface SEM scanning found the junction magnesium plate and aluminum plate is straight and magnesium alloy side tends to expand to the aluminum side, there are many diffuse distribution of white particles near the interface phase. EDS analysis concluded that the particle area is composed of mixture of Al12Mg17and Al3Mg2.On the basis of FSSW, doing Bonding-FSSW test. First determining the order of welding process, then optimizing the process parameters, the research shows that:under the same process, the shear resistance of Bonding-FSSW joint is generally higher than that of single spot welding and bonding alone, which says that bonding and spot welding have a good combination, and increase welding time appropriately on the basis of single spot welding can increase the joint strength. Finally, also choose the better process parameters to analysis the joint microstructure and performance, microstructure analysis shows that in the border of Al/Mg interface formed a diffusion layer composed of magnesium alloy, aluminum alloy and the adhesive, the diffusion layer nearby has the highest hardness, the reason is that there might be a near the brittle inter metallic compound, XRD found that the diffusion layer exists Al17Mg12brittle inter metallic compounds, and this is the main reason of brittle fracture. |
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