Key Takeaways & Executive Findings
- •• Cooling rate critically controls the volume fraction of Al-Li phases (AlLi and MgLi2Al) in annealed LAZ832 alloy, with slower cooling increasing their presence. • Solid solution strengthening from Al and Zn dissolution enhances tensile strength but reduces ductility at high solute levels. • Air cooling achieves the best balance of strength, ductility, and corrosion resistance, outperforming furnace cooling and offering a compromise over water quenching. • Elevated work function, measured by SPM, correlates with improved corrosion resistance due to solute dissolution.
Abstract
Annealing treatment is an effective strategy to enhance the comprehensive properties of Mg-8Li-3Al-2Zn (LAZ832) alloy, where the cooling rate plays a decisive role in tailoring microstructure and performance. This study systematically investigates the effects of cooling rates, controlled via water quenching (WC), air cooling (AC), and furnace cooling (FC), on the phase evolution, mechanical properties, and corrosion resistance of LAZ832. The annealed microstructure consists of α-Mg, β-Li, AlLi, and MgLi2Al phases, and the volume fraction of Al-Li phases (AlLi and MgLi2Al) increases as the cooling rate decreases. Strengthening mechanisms are dominated by solid solution strengthening, driven by the dissolution of Al and Zn atoms into the matrix, which significantly enhances tensile strength. However, excessive solute content leads to a marked decline in ductility. Scanning probe microscope (SPM) reveals an elevated work function due to the dissolution of Al and Zn atoms into the matrix phase, correlating with improved corrosion resistance. Comprehensive analysis demonstrates that air cooling achieves an optimal balance between tensile strength, ductility, and corrosion resistance, outperforming furnace-cooled samples and offering a pragmatic compromise compared to water-quenched specimens with higher strength but brittle failure. These findings establish a robust framework for designing LAZ832 alloys with tailored microstructures and multi-property optimization, advancing their application in lightweight engineering fields.
1. Introduction
Magnesium (Mg) alloys find extensive applications in the industrial field owing to their low density and high specific strength [1-3]. To further pursue reduction of density and enhancement of comprehensive properties, the lighter element, Li, is added into Mg alloys. Magnesium-lithium (Mg-Li) alloys are distinguished as the lightest metallic structural materials, with a density below 1.5 g·cm-3 [4, 5]. The introduction of Li reduces the axial ratio (c/a) and leads to the formation of a ductile β-Li phase with a body-centered cubic structure, which substantially enhances the plastic deformation capability. This improvement makes Mg-Li alloys increasingly desirable for applications requiring lightweight and malleable materials [6].
However, the Mg-Li alloy system faces two drawbacks that hinder its broader application. With the increase of Li content, the tensile strength decreases due to the increase of β-Li phase. When the Li content surpasses 10.3wt.%, the tensile strength can fall to approximately 100 MPa, which is notably lower than that of commercially used Mg alloys [7]. Moreover, the already poor corrosion resistance of Mg alloys is further deteriorated with the addition of Li, owing to the highly reactive chemical nature of Li [8, 9].
The multi-componentization design has been proven effective in improving the comprehensive properties of the Mg alloys. The addition of Al to the Mg alloy, for example, improves the yield strength and hardening rate during plastic deformation by reducing stacking fault energy and promoting dislocation slipping along the basal plane [5, 10]. The introduction of Zn to the Mg-Li alloy provides a substantial solid solution strengthening effect, enhancing the mechanical stability, ductility, and plasticity of the second phase [11]. Therefore, present research attention is focused on the Mg-Li-Al-Zn alloys. Heat treatment can further enhance the tensile strength of Mg-11Li-3Al alloy to over 400 MPa [12]. Furthermore, the passive film can be formed during the corrosion process due to the dissolution of Al into the matrix phase [13]. In the case of the Mg-8Li-3Al-2Zn-0.5Y alloy, a trade-off between tensile strength and corrosion resistance is achieved, with a maximum tensile strength of 265.7 MPa due to the dissolution of the AlLi phase into the matrix phase [14]. In the Mg-9Li-3Al-1Zn alloy, the synergistic optimization in strength-ductility-corrosion is attained through the introduction of cross-pass friction stir processing [15], facilitated by the unique distribution of the α-Mg/β-Li phases and ultrafine MgLi2Al precipitates.
The previous studies highlight that the Mg-Li-Al-Zn alloys exhibit a significant improvement in comprehensive properties through multi-componentization design. Nevertheless, it is observed that the Mg-Li-Al-Zn alloys show decreasing plasticity with the increasing content of s
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Ling Li, Wang-yang Xue, Zhu-min Li, Tian-yu Liu, Rui Zheng, Guo-bing Mao (2025). Microstructural evolution and comprehensive properties of Mg-8Li-3Al-2Zn alloy during annealing treatment under various cooling rates. China Foundry. https://doi.org/10.1007/s41230-025-3113-6
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Frequently Asked Questions
What is the effect of cooling rate on the microstructure of Mg-8Li-3Al-2Zn alloy?
Slower cooling rates (e.g., furnace cooling) increase the volume fraction of Al-Li phases (AlLi and MgLi2Al) in the annealed microstructure, while faster cooling (water quenching) suppresses their formation.
How does cooling rate influence the mechanical properties of LAZ832 alloy?
Water quenching yields higher tensile strength due to solid solution strengthening but results in brittle failure. Air cooling provides a balanced combination of strength and ductility, while furnace cooling leads to lower strength and ductility.
What is the relationship between work function and corrosion resistance in this alloy?
The dissolution of Al and Zn atoms into the matrix increases the work function, which correlates with improved corrosion resistance.
Which cooling condition is optimal for achieving balanced properties in LAZ832 alloy?
Air cooling achieves the optimal balance between tensile strength, ductility, and corrosion resistance, making it a pragmatic choice for engineering applications.
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