| 1 | Pinless Friction Stir Spot Welding of Mg-3Al-1Zn Alloy with Zn Interlayer显示文摘With the addition of a thin Zn interlayer,2.4 mm thick Mg-3Al-1Zn alloy sheets were friction stir spot welded(FSSW) using a pinless tool with flat,convex and concave shoulder shapes. The results showed that an alloying reaction took place between the Mg substrate and Zn interlayer during FSSW,forming a discontinuous intermetallics layer composed of dispersive(α-Mg+MgZn) eutectic structure underneath the shoulder and a Mg-Zn intermetallics bonding zone at the outside of the joints. This alloying reaction increased the bonded area and eliminated the hook defects,thereby producing sound FSSW joints with a shallow keyhole without hook defects. The increase of plunge depth was beneficial to the Mg-Zn diffusion,thereby increasing the tensile-shear load of the joints. However,excessive plunge depths resulted in a decrease of the effective sheet thickness,reducing the strength of the joints. At a small plunge depth,the convex and concave shoulders were more beneficial to the interface reaction than the flat shoulder. The maximum joint load of 6.6 kN was achieved by using the concave shoulder at a plunge depth of 1.0 mm. A post-welding heat treatment promoted the dissolution of the discontinuous reaction layer in the joints; however,it led to the occurrence of void defects,influencing the bonding strength. | R.Z.Xu D.R.Ni Q.Yang C.Z.Liu Z.Y.Ma | 2016 | Journal of Materials Science & Technology2016，32，1： | 12 |
| 2 | Influencing mechanism of pre-existing nanoscale Al5Fe2 phase on Mg-Fe interface in friction stir spot welded Al-free ZK60-Q235 joint显示文摘Al-free ZK60 magnesium (Mg) alloy sheet was selected as substrate material of Mg-steel pinless friction stir spot welding (FSSW), avoiding the effect of the Al element in the substrate on the alloying reaction of Mg-iron (Fe) interface. The sound FSSW joint of ZK60 Mg alloy and Q235 steel with a hot-dipped aluminum (Al)-containing zinc (Zn) coating was successfully realized. The detailed microstructural examinations proved that Al5Fe2 phase at the Mg-Fe interface came from the pre-existing Al5Fe2 phase in the coating and acted as the transition layer for promoting the metallurgical bonding of Mg and Fe. The interfaces with well-matched lattice sites among Fe, Al5Fe2 and Mg were formed during FSSW. A low energy interface with good match of lattice sites ((002)Al5Fe2//(110)Fe, [110]Al5Fe2//[113]Fe) between Al5Fe2 and Fe was identified. For the interface between Al5Fe2 and Mg, an orientation relationship of (622)Al5Fe2//(3112)Mgand[158]Al5Fe2//[2423]Mg was observed. The tensile-shear load of the ZK60-steel joint could reach 4.6 kN. Moreover, the joint fracture occurred at the interface between the Al5Fe2 layer and the Mg alloy substrate, suggesting the brittle fracture characteristic. | R.Z.Xu Q.Yang D.R.Ni B.L.Xiao C.Z.Liu Z.Y.Ma | 2020 | Journal of Materials Science & Technology2020，42，7： | 2 |
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