Effect of Solid Solution Temperature on the Microstructure and Mechanical Properties of Al-5Mg-2.5Li Alloy

This study systematically investigates the effects of solution treatment (S. S.) temperature (450-500 degrees C) on the microstructure, mechanical properties, and Portevin-Le Chatelier (PLC) effect of Al-5Mg-2.5Li alloy. At lower S. S. temperatures (450-470 degrees C), the alloy retained a fine grain size (similar to 9 mu m) with minimal Li oxidation, whereas higher temperatures (480-500 degrees C) induced grain coarsening (>50 mu m) and severe Li oxidation, forming 10 mu m-wide Li2O bands. Precipitation strengthening dominated the mechanical performance: aging at 450 degrees C after S. S. produced dense delta '-Al3Li precipitates. Its hardness can reach 142 HV, and its tensile strength is 502 MPa. High-temperature S. S. (500 degrees C) suppressed delta '-Al3Li formation due to Li oxidation. The PLC effect exhibited temperature-dependent behavior: aged alloys at 450-470 degrees C showed higher stress drops (Delta sigma: similar to 3.9 MPa in aging) and B/C-type serrations, attributed to delta '-Al3Li shearing and solute-dislocation interactions. At 480-500 degrees C, reduced Li content shifted PLC to Mg-dominated C-type serrations with lower stress drops (Delta sigma: similar to 2.3 MPa in aging) and higher critical strain (epsilon(C): similar to 5.3% versus similar to 3.5% at 450-470 degrees C). These findings underscore the critical role of S. S. temperature in balancing Li oxidation, precipitation kinetics, and PLC behavior, guiding the design of high-performance Al-Mg-Li alloys.