根据已有的实验结果提出了Al－Mg－Si系合金均匀化过程中片层状β－AlFeSi相向球形α－Al(FeMn)Si相转变过程模型图, 并据此采用稳态扩散理论对其转变动力学过程以及555 ℃不同时间相转变过程等进行了系统深入的研究. 结果表明, 均匀化温度T对β→α相转变的动力学影响很显著, 温度越高, 转变速率越快; 而α相原始核心的大小只略微影响β相溶穿时间; α相核心间距l主要影响转变过程中β相的边界溶解阶段; β相的厚度对β→α相转变过程的影响最大, 特别是溶穿阶段, 随着厚度的增加,转变过程由β相边界溶解为主导的方式向由β相溶穿为主导的方式发生转变; 当β相厚度分别为0.1,0.2和0.3 μm时, 理论预测发生熔断所需均匀化时间分别大于5, 10和15 h, 这与实际的实验结果非常吻合. 此外,β相厚度小于0.3 μm时, 经16－24 h很容易达到转化率f(α) ≥0.9, 因此, 除了优化均匀化过程进而更好地控制β→α相转变之外, 合金熔铸工艺也应该尽量保证基体内的β相厚度小于0.3 μm.

According to the present experiment results about the transformation from β－AlFeSi to α－Al(FeMn)Si phase in Al－Mg－Si series alloys, the model and kinetics of phase transformation,and microstructure evolution at 555 ℃ were systematically investigated. The results show that, the homogeneous temperature T can give a significant effect on the transformation kinetics, and with increasing T, the transformation rate increases fast. The nucleus radius of α phase only affects the breakthrough time along the thickness direction of β phase. The distance l between twoα phases mainly has an influence on the dissolving of rim for β phase. The thickness of β phase normally has a greatest influence on the phase transformation β→α,especially for the breakthrough stage of β phase, with increasing the thickness of β phase,the main transformation with longer time in the whole phase transformation process can changes from rim dissolving of β phase to breakthrough along the thickness direction of β phase. The breakthrough time of β phases with the thickness of 0.1, 0.2 and 0.3μm is above 5, 10 and 15 h, respectively, which corresponds with the real experiment results. In addition, if the thickness of β phase is smaller than 0.3μm, the transformation rate f(α) easily reaches above 0.9 after homogeneous heat treatment at 555 ℃ for 16－-24 h. Therefore, the importance of optimizing casting process to make sure the thickness of β phase below 0.3μm, is the same as the homogeneous heat treatment for the better controlling the phase transformation β→α.