Effects of Solution Treatment on the Microstructural Evolution and Mechanical Behavior of an Extruded Mg-Li-Al-Zn-Ca Alloy after Long-Term Natural Aging

Authors:
  • SYShuaiping Yang
    Shuaiping Yang
  • RWRuihao Wei
    Ruihao Wei
  • HYHuiHui Yang
    HuiHui Yang
  • YPYang Pu
    Yang Pu
  • YZYirong Zhang
    Yirong Zhang
  • DZDan Zhang
    Dan Zhang
  • QWQi Wei
    Qi Wei
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Abstract
The microstructural evolution and mechanical properties of a dual-phase Mg-9Li-4Al-1.5Zn-0.2Ca alloy subjected to 30 d of natural aging followed by solution treatment at 350 °C were systematically investigated. After natural aging, the alloy exhibited pronounced interphase partitioning of Al, multiscale second-phase particles, and a high density of deformation-induced defects. After solution treatment at 350 °C х 0.5 h, the Al-Zn-rich particles were partially dissolved, promoting solute redistribution, while MgLi2Al-type nanoprecipitates, Al2Ca particles, and dislocation structures were largely retained. Consequently, the ultimate tensile strength increased from 288 to 372 MPa, while a high elongation of 14.8% was maintained. With increasing holding time, Al progressively evolved toward a more homogeneous distribution between the two matrix phases. Distinct precipitation behaviors were observed within the β-Li grains and at the α-Mg/β-Li interfaces, accompanied by dislocation rearrangement and phase coarsening, resulting in non-monotonic variations in strength and ductility. These results demonstrate that the strengthening response during solution treatment after prolonged natural aging is governed by the synergistic effects of second-phase dissolution, solute redistribution, spatially heterogeneous precipitation, and defect-structure evolution.

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