热处理对AZ91D镁合金显微组织的影响

Influences of Heat Treatment on Microstructure of AZ91D Magnesium Alloy

研究了铸态、固溶及时效AZ91D镁合金的微观组织,分析了热处理对合金组织和显微硬度的影响。结果表明,薄片状共晶α相和粗大块状β相的热稳定性都不高,但可分别经过380和410℃固溶处理加以消除;Al-Mn相主要呈颗粒状或针状,尺寸为10～50μm,经410℃×24h固溶处理未发生明显改变。固溶样品经200℃×12h时效后有大量长10μm、直径1～2μm的杆状相析出,且主要垂直或斜交于基体,但当时效温度继续升高时析出相将转变为大部分平行于基体分布,使第二相的强化效果减弱。

The microstructure of as-cast, solution-treated and aged AZ91D magnesium alloy was studied. The influences of heat treatment on microstructure and microhardness of the alloy were analyzed. The results show that the thermal stability of laminar α phase and blocky β phase are not good, but can be eliminated by solution treatment at 380 ℃ and 410 ℃ respectively. Al-Mn phases, on the other hand, are the morphologies of granule and aciculae with the dimension of 10 to 50 μm, and keep almost unchanged during solution treatment （410 ℃ × 24 h）. A large amount of second phases in the forms of rod with dimension of 10 μm, φ1--φ2μm are precipitated after aging at 200 ℃ for 12 h, and are perpendicular to or crossed with the matrix. Such precipitates will change into the ones which are mainly parallel to the matrix when aging temperature increases further. As a result, the strengthening effect of precipitates declines.