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采用冷却速率为0.01~3 K/s的差示扫描量热法(DSC)和冷却速率更高的淬火膨胀法研究铸态Al-7Si-0.3Mg合金淬火的析出行为。在合金冷却的过程中发生了两种析出反应,高温反应开始于淬火起始温度540°C,低温反应始于400°C左右。3 K/s的淬火冷却速率已经显著抑制淬火过程中相的析出。合金T6态的硬度随着淬火速率的增快而增加,这是由合金过饱和固溶度增加而导致的。通过膨胀实验和硬度实验的结果可以估计临界冷却速率大约为60 K/s。通过光学显微镜观察淬火态的铸态Al-7Si-0.3Mg合金的显微组织。结果表明:根据淬火冷却速率的不同合金的显微组织由铝-硅共晶组织、铝固溶体枝晶及枝晶间的析出相组成。
The precipitation behavior of the as-cast Al-7Si-0.3Mg alloy during quenching was investigated by differential scanning calorimetry (DSC) with cooling rate of 0.01-3 K / s and quenching-expansion method with higher cooling rate. Two precipitation reactions occurred during the cooling of the alloy. The high temperature reaction started at a quenching start temperature of 540 ° C and the low temperature reaction started at about 400 ° C. The quench cooling rate of 3 K / s has significantly inhibited the precipitation of phases during quenching. The hardness of the alloy T6 state increases with the quenching rate, which is caused by the increase of supersaturated solid solubility of the alloy. The critical cooling rate can be estimated to be about 60 K / s from the results of the expansion and hardness experiments. The microstructure of the as-cast Al-7Si-0.3Mg alloy in as-quenched state was observed with an optical microscope. The results show that the microstructures of different alloys based on the quench cooling rate are composed of aluminum-silicon eutectic microstructure, aluminum solid solution dendrite and precipitation phase between dendrites.