轻质金属的发展和应用：高强铝合金和镁合金

The influence of hierarchical aging temperature and time on the microstructure and properties of 7A85 a-luminum alloy panel was investigated by the mechanical property test and microstructure analysis. The results indicate that the precipitate phase in 7A85 aluminum alloy after single stage aging are mainly composed of Al₂Cu phase, Mg₂Zn₁₁phase, and G.P. II region, which are semi-coherent with the a-Al matrix, showing excellent plasticity while maintaining high strength. The precipitates of two-stage aging are MMg₂Zn₁₁, Mg_3.5Zn_1.5, and MgZn₂, and the strengthening mechanism is characterized by the semi-coherent lattice distortion strengthening between the G.P. II region or Mg₂Zn₁₁phase and the α-Al matrix, showing a rise of yield strength and hardness as well as descent of the plasticity. The precipitate phase is transformed into Mg₂Zn₁₁, MgZn₂. and Al₂CuMg phases as the aging process continues, where MgZn₂is the major, and the lattice relationship between the MgZn₂phase and the α-Al matrix is converted to incoherent completely,leading to a decline of strength, and continuous increase of plasticity under the influence of α-A1 matrix.