Al-Zn-Mg-Cu合金半固态等温组织粗化研究

Study on the Microstructure Coarsening of Al-Zn-Mg-Cu Alloy during Semi-Solid Isothermal Heat-Treatment

摘要:

采用半固态等温热处理方法，研究了Al-Zn-Mg-Cu合金在加热到两相区温度等温保温过程中的组织粗化规律。回归拟合结果表明，α(Al)晶粒平均直径与等温时间近似满足方程：，粗化速率系数K随等温温度升高而增大，其在610和620 ℃下对应的值分别为14811.4和17836.3 μm4/s。实验合金组织的多边化、球化和粗化现象是同时发生的，组织粗化以晶粒合并长大和Ostwald熟化的方式进行。等温前期粗化以合并为主，但随着晶间液相增多，合并变得困难，导致等温后期粗化速率下降

Abstract:

Using semi-solid isothermal heat-treatment, the behavior of grain coarsening of Al-Zn-Mg-Cu alloy at the temperatures in solid-liquid two phase region was studied. The results from regression analysis show that the relationship between the average diameter of α(Al) grains and the isothermal holding time nearly fits the formula . In the formula, the coefficient of coarsening rate K increases with the increase of the isothermal temperature, which equals to 14811.4 μm4/s at 610 oC and 17836.3 μm4/s at 620 oC, respectively. The microstructure’s polygonizing, spheroidizing and coarsening of the experimental alloy occur simultaneously; among them the coarsening is caused by the coalescence between the adjacent grains and Ostwald ripening. During the early stage of the isothermal treatment, the coarsening is governed by the coalescence growth, but the coalescence becomes more and more difficult with the increase of the liquid fraction, which results in the decrease of the coarsening rate in the late stage