Varying welding speeds and their effect on the microstructure and properties of Mg-9Li-3Al-3Zn alloy

Abstract

Abstract Friction stir welding was used to join the duplex-structured Mg-9Li-3Al-3Zn alloys. The effects of welding speed on microstructure and mechanical properties were investigated. After FSW, the nugget zone(NZ) experienced grain refinement, and the α phase dissolved into the β phase. The minimum grain size of α phase is 6.51 μm and the minimum α/β ratio is 3.33%. The welding heat primarily facilitated the solution of the Mg17Al12 and AlLi phases into the matrix. MgLi2Al, a new phase, was formed in NZ. Microstructure changes lead to an overall increase in joint hardness. At a 500 mm/min welding speed, the joint exhibited UTS 162.94 MPa, comparable to the base metal. The corrosion resistance of the joint was enhanced due to grain refinement and a decreased α/β phase ratio. The self-corrosion current of the alloy was reduced from 4.298×10-5 A/cm2 to 2.06×10-4 A/cm2 in NZ. The corrosion products were confirmed to be Mg(OH)2, Al(OH)3 and Li2CO3.