Effect of heat treatment on microstructure evolution, strengthening-toughening and corrosion behavior of high-strength LA103Z Mg-Li alloy fabricated by wire-arc additive manufacturing

Abstract

This study investigated the effects of heat treatment on the mechanical and corrosion properties of cold metal transfer-based wire arc additively manufactured (CMT-WAAM) LA103Z magnesium-lithium alloy. The results demonstrated that both solid solution treatment and aging treatment improved the mechanical properties of the alloy, while the corrosion resistance of the solid solution-treated alloy was significantly enhanced. The solid solution treatment (340°C) dissolved the fine needle-like α-Mg and AlLi phases, and the Li₂MgAl phase precipitates were dispersed. The ultimate tensile strength of the solution-treated alloy increased significantly from 144 ± 6.2 MPa to 299 ± 1.2 MPa, an increase of almost 107.6%. The high-temperature (225°C) aging treatment made the alloy grain distribution more uniform, caused the AlLi phase particles to gradually coarsen, and transformed the Li₂MgAl phase into a substantial quantity of fine AlLi phase particles. The yield strength increased from 100 ± 5.0 MPa to a maximum of 182 ± 2.6 MPa, representing an approximately 82% increase, while the maximum elongation reached 24.1% ± 2.0%. The electrochemical test results showed that the fine equiaxed grains and uniformly distributed fine needle-like α-Mg phase in the As-built sample reduced micro galvanic corrosion sensitivity and enhanced corrosion resistance compared to the rolled sample. The AlLi phase particles in the solid solution-treated sample were nearly completely dissolved, leading to a significant reduction in micro-galvanic corrosion between the secondary phases and the matrix. Corrosion primarily occurred along the interface between the α-Mg and β-Li phases, exhibiting filamentary corrosion, and the sample showed the highest corrosion resistance. In contrast, the samples subjected to direct high-temperature aging and solution treatment followed by aging exhibited exacerbated local corrosion due to the coarsening of the AlLi phase and the increased amount of precipitation.