【摘要】 研究了等温热处理温度和保温时间等工艺参数对AZ91D镁合金半固态组织演变和成形性的影响。结果表明 ,半固态等温热处理可以将普通金属型铸造的AZ91D镁合金锭中的枝晶组织转变为球形晶粒组织 ,其演变过程为 :在升温过程中晶界处部分γ相先发生溶解 ,随着温度的升高 ,剩余的γ相开始熔化 ,继而δ相也发生熔化 ,并在等温处理中逐渐演变为球状 ;保温温度越高 ,半固态重熔和δ相演变过程越快 ,保温温度过高或保温时间过长 ,试样易发生变形 ,同时 ,球状晶粒也容易趋于长大。AZ91D镁合金半固态成形所需的最佳工艺条件为加热温度 5 70℃左右 ,保温时间 2 5～ 35min ;或加热温度 5 80℃左右 ,保温时间 15～ 2 0min。更多还原

【Abstract】 The effects of isothermal temperature and holding time on microstructure evolution and forming of AZ91D magnesium alloy in semi-solid state were studied. The results show that the semi-solid isothermal heat-treatment can turn the dendritic structure of AZ91D magnesium alloy by permanent mould cast into spheroids. The process is as following: during the increasing of temperature, the partial γ phase at grain interface of eutectic structure is dissolved first; then with the further increasing of temperature, the residual γ phase and the δ phase begin to remelt successively and the δ phase gradually evolves into spheroidal shape during the holding. The higher the isothermal temperature, the faster the semi-solid remelting of samples and the δ phase evolution process. When the isothermal temperature is much higher or the holding time is much longer, the samples are susceptible to deformation. And the spheroidal structure is also susceptible to grow up. The best semi-solid structure for semi-solid-forming can be obtained at about 570 ℃ and the holding time about 30～45 min, or about 580 ℃ and the holding time about 15～25 min.更多还原