摘要:
研究了Mg-Sn-Si系合金的热力学基础及合金相的演变过程.结果表明：对于Mg-Sn-Si系合金,合金相的比热容随着温度增加而增加,在低温下变化迅速,而在高温下变化平缓,其热膨胀系数在低温范围内随温度升高呈指数形式增加,而在高温范围内呈线性增大.在Mg2(Six, Sn1?x)、Mg2(Snx, Si1?x)相结构中, Sn(Si)原子的取代位置不固定,可以是面心,也可以是顶点.常规凝固过程中,由于处于非平衡状态,x的取值范围有所波动,对于Mg2(Six, Sn1?x)和Mg2(Snx, Si1?x)两种结构, x的取值范围在0.25或0.75附近. Mg2(Si, Sn)的生成温度较高,可从液相中直接析出,也可由Mg2Si转化而来,而Mg2(Sn, Si)的生成温度较低,只能从基体中析出,随着Sn含量的增加,开始析出Mg2(Sn, Si)相的温度升高.
Abstract:
Thermodynamics basic and alloy phase evolution of Mg-Sn-Si alloy are studied. The results indicate that for Mg-Sn-Si alloy, the specific heat of alloy phase increases with temperature, and it changes quickly at low temperature while gently at high temperature. In the range of low temperature, its thermal expansion increases exponentially with the increase of temperature, and in the range of high temperature the thermal expansion increases linearly. In the two structures of Mg2 (Six, Sn1?x) and Mg2 (Snx,Si1?x) phases, the replacement position of Si or Sn is indefinite, they could be face-center location or vertex location. Under the conditions of conventional solidification, the range of values for x is fluctuant, for it is in nonequilibrium state: x values are around 0.25 and 0.75 for Mg2(Six, Sn1?x) and Mg2(Snx, Si1?x) structure, respectively. The generation temperature of Mg2 (Si, Sn) phase is quite high, it can be precipitated directly from liquid phase, or be transformed from Mg2Si. The generation temperature of Mg2(Sn, Si) phase is lower than that of Mg2(Si, Sn), and it can be precipitated only from the matrix, the initial precipitation temperature of Mg2(Sn, Si) tends to rise with Sn content increasing.
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