Top issue of magnesium alloy "JMA": Progress has been made in the study of heat treatment to control the microstructure of magnesium lithium alloys and improve their corrosion resistance

Magnesium lithium alloy, as a metal material for ultra light structures, has broad application prospects in fields such as aerospace, electronic products, and rail transportation. However, its low mechanical properties and poor corrosion resistance greatly limit its application. Zn is one of the common alloying elements in magnesium lithium alloys, which can improve the mechanical processing performance, mechanical properties, and corrosion resistance of magnesium lithium alloys. Through heat treatment, the precipitated phase θ '- MgLi2Zn can be obtained, thereby improving the mechanical properties of magnesium lithium alloys. However, the metastable θ 'phase gradually transforms into a stable θ - MgLiZn phase at room temperature, resulting in a decrease in the mechanical strength of magnesium lithium alloys and typical aging softening phenomena. Although the evolution law of the second phase and its influence mechanism on the mechanical properties of magnesium lithium alloys after adding Zn element have been reported, there is relatively little research on the influence of the evolution of the second phase and matrix substructure on the corrosion resistance of magnesium lithium alloys during heat treatment, and the relevant mechanism is unclear. Recently, the research team of Academician Han Enhou from our institute has made significant progress in the study of the corrosion mechanism of magnesium lithium alloys in collaboration with Guangdong University of Technology. They have found that appropriate heat treatment processes can regulate the second phase in magnesium lithium alloys, thereby significantly improving their corrosion resistance. The research result is titled "Improving the corrosion resistance of an ultra lightweight BCC Mg Li Zn alloy via controlling the microstructure by heat treatment" and was published in the top journal in the field of magnesium alloys, Journal of Magnesium and Alloys (IF: 15.8). The first corresponding author of the paper is Associate Professor Li Chuanqiang from Guangdong University of Technology, and the co corresponding authors are Associate Researcher Bian Dong from Guangdong Provincial People's Hospital and Associate Researcher Yan Changjian from our hospital.

This study regulates the microstructure of as cast Mg-14Li-8Zn alloy through heat treatment, which can significantly improve its corrosion resistance and demonstrate the corrosion mechanism of alloys with different microstructures. This research achievement not only deepens the understanding of the microstructure evolution and corrosion resistance of BCC structured Mg Li Zn alloys, but also provides important theoretical support for the design and application of high-strength, high corrosion resistant, and ultra light magnesium lithium alloys, which has important guiding significance in material design and engineering applications.

This study obtained the microstructure of Mg-14Li-8Zn alloy with BCC structure through heat treatment, and systematically studied the microstructure evolution of the alloy from cast state to solid solution state to aging state, as well as the corrosion mechanism of the three in 0.1 mol/L sodium chloride solution. The results show that there are a large number of continuous β - Li/θ 'eutectic phases in the as cast alloy, and strong micro galvanic corrosion effects occur during the corrosion process. In addition, there are a large number of dislocations in the matrix, leading to lattice distortion and further reducing the corrosion resistance of the alloy due to the local stress generated. After solution treatment, a large number of nano precipitates θ 'are evenly distributed in the alloy matrix, and the dislocations in the matrix are significantly reduced. The corrosion process can also form a good surface facial mask, showing the best corrosion resistance. After aging treatment, θ 'phase grows larger and forms θ phase. θ phase and β - Li produce obvious micro galvanic corrosion and destroy the integrity of the surface facial mask. Therefore, the corrosion resistance of aging alloy is lower than that of solid solution alloy, but still better than that of as cast alloy.