Effect of processing parameters on the microstructure and tensile properties of a dual-phase Mg–Li alloy during friction stir processing

Abstract

A dual-phase Mg–Li alloy LA103Z sheet was subjected to single pass submerged friction stir processing (FSP) at various of tool sizes, rotation rates and travel speeds. The relationships between processing parameters, frictional heat generation, microstructure, and the room-temperature tensile properties of LA103Z in the stir zone were systematically investigated. Both the α-Mg phase and the β-Li phase undergo complete dynamic recrystallization, the grains are significant refined and the texture is significantly weakened. The precipitation of the AlLi phase and the Li2MgAl phase are promoted by FSP. With the increase of the tool size and rotation rate, the average grain size of the FSPed LA103Z rises as well as the tensile strength, showing an inverse Hall–Petch relation. This is owing to the solid-solution strengthening effect and the reduction of the α/β phase boundaries caused by the dissolution of the α-Mg phase. After being processed by a 16 mm-diameter-shoulder stirring tool under the rotation rate of 800 rpm and the traverse speed of 100 mm/min, the ultimate tensile strength of the FSPed LA103Z is remarkably improved from 177.92 MPa (base metal, BM) to 268.04 MPa, showing the best mechanical property.