Influencing mechanism of pre-existing nanoscale Al5Fe2 phase on Mg-Fe interface in friction stir spot welded Al-free ZK60-Q235 joint

• 来源期刊: 材料科学技术（英文版）
• 年，卷（期）: 2020,（7）
• 页码范围: 220-228
• 页数: 9页
• 语种: 英文

摘要

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//[(1)13]Fe) between Al5Fe2 and Fe was identified.For the interface between Al5Fe2 and Mg,an orientation relationship of (6(2)2)Al5Fe2//(3(112))Mg and[1(58)]Al5Fe2//[2(4)23]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.