| Abstract: | 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 succes s fully realized.The detailed micro structural examinations proved that Al_5 Fe_2 phase at the Mg-Fe interface came from the pre-existing Al_5 Fe_2 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,Al_5 Fe_2 and Mg were formed during FSSW.A low energy interface with good match of lattice sites((002)_(Al5 Fe2)//(110)_(Fe),[110]_(Al5 Fe2)//[113]_(Fe)) between Al_5 Fe_2 and Fe was identified.For the interface between Al_5 Fe_2 and Mg,an orientation relationship of(622)_(Al5 Fe2)//(3112)_(Mg) and[158]_(Al5 Fe2)//[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 Al_5 Fe_2 layer and the Mg alloy substrate,suggesting the brittle fracture characteristic. |
