Abstract
Developing light structure materials that work stably at elevated temperatures is a long-standing challenge for many application fields, particularly in the development of aerospace equipment. Zn/Cd alloying elements were prospected to improve the stability of the lightest Mg-Li based alloys; however, little is known about the intermediate-temperature mechanical properties of such alloys. The present work investigated the tensile behaviors of a cold-rolled Mg-Li-Al-Cd-Zn alloy in a temperature range of 30–150 °C. The results indicate that the alloy can host a tensile strength σUTS of 108~121 MPa, a yield strength σYP of 97~109 MPa and elongation εB of 14–15 % at 150 °C, dependent on the tensile direction. The mechanical properties intensively are modulated by temperature through the competition between work hardening and softening. Work hardening due to dislocation blocking by the precipitated MgLi2X phase dominated the deformation at low temperatures, while softening that resulted from dynamic recrystallization was the main effect at high temperatures. Correspondingly, a quasi-cleavage mechanism dominated the fracture at temperatures near room temperature, and microvoid coalescence worked at high temperatures above 100 °C. Our results offer a new experimental understanding of the elevated-temperature mechanical behaviors of Mg-Li alloys and will advance the development of new light magnesium alloys with high stability.
Highlights
As the lightest structural metal material, Mg-Li alloys are expected to be widely used in the aerospace, health care, automobile and electronic industries because of their low density, high specific strength and elastic modulus, excellent formability and damping property [1–4]
Typical duplex phases were confirmed by the optical microscopy (OM) metallographic analysis (Figure 2a) and by transmission electronic microscopy (TEM) at a low magnification scale (Figure 2b)
The two phases were assigned as the α-Mg phase and β-Li phase by a combination of the XRD and energy dispersive spectrum (EDS) analysis results and the reported scales
Summary
As the lightest structural metal material, Mg-Li alloys are expected to be widely used in the aerospace, health care, automobile and electronic industries because of their low density, high specific strength and elastic modulus, excellent formability and damping property [1–4]. It is well documented that Mg-Li alloys with a hexagonal closed-packing structure phase (hcp-α) have a moderate strength and a limited formability, while the body-centered cubic structure phase (bcc-β) Mg-Li alloy demonstrates an excellent workability but notably lower strength [7,8]. A big challenge for Mg-Li alloy application is the low stability due to the high mobility of lithium atoms and vacancies even under room temperature, which could be relieved by the addition of Zn and Cd in the MA21 alloy [9]. It is necessary to investigate the elevated temperature mechanical properties of this material
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