Microstructural Modification by Large Pre-Deformation and Post-Aging to Improve Properties in Al-Mg-Li Alloy

Abstract

Al-Mg-Li alloy is an ideal lightweight structural material for aerospace applications due to its low density, high specific strength, and excellent low-temperature performance. This study examines the mechanical properties and microstructural evolution of Al-Mg-Li alloy subjected to cryogenic and room temperature cold rolling, which induces large plastic deformation. Compared with room temperature rolling, cryogenic rolling significantly reduces surface cavity formation, thereby enhancing the alloy’s rolling surface quality. After cryogenic rolling by 80% and subsequent natural aging, the yield strength of artificially aged Al-Mg-Li alloy reaches 560 MPa, delivering a 60% increase compared to the traditional T6 state with a slight reduction in elongation from 6.5% to 4.6%. The specific strength achieves 2.23 × 105 N·m/kg, outperforming conventional Al-Cu-Li and 7xxx-series Al alloys. The depth of intergranular corrosion decreases from 100 µm to 10 µm, demonstrating excellent corrosion resistance enabled by the new method. Transmission electron microscopy reveals that finely distributed δ′ (Al3Li) is the primary strengthening phase, with high-density dislocations further enhancing strength. However, coarsening of δ′ (from ~2.9 nm to >6 nm) induced by ensuing artificial aging results in coplanar slip and reduced elongation. Lowering the post-aging temperature inhibits δ′ coarsening, thereby improving both strength and elongation. Our results provide valuable insights into optimizing the properties of Al-Mg-Li alloys for advanced lightweight applications.

Keywords

• Al-Mg-Li alloy
• cryogenic rolling
• artificial aging
• mechanical properties
• microstructural evolution