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本文所研制的热分析装置用于快速测定铝硅合金的组织细化和变质效果,能在三分钟内完成测试过程。本热分析装置的特色是:(1)采用了高精度,多功能的测试仪器,它不仅可以测出温度与时间的关系曲线,还能测试相应的微分曲线,其温度绝对误差:ΔT≤±0.3℃;(2)对热分析样杯作了一系列试验。确定了适合铝硅合金的热分析样杯结构及材料,从而提高了测量结果的准确性和重复性。本文系统研究了Ti,Na,Sb,Sr,Re对亚共晶铝硅合金的变质及其对热分析曲线上特征值的影响,获得了能评估其变质程度的热分析判据。用Na,Sr,Re变质时,从未变质到变质良好,共晶生长温度TEG,共晶形核过冷度ΔTE;呈减小的趋势,共晶过冷度ΔT则呈增加趋势。用Sb变质时,从未变质到良好变质,ΔTE和ΔT呈增加趋势,TEG呈减小趋势,随着Ti量的增加,α初晶形核最低温度升高,初晶形核过冷度减小。以牛顿传热方程和热力学理论为基础,结合铝硅合金热分析曲线,可推导出液态合金凝固过程中固相分数,固相生长速度,固相生长加速度的方程,为铝硅合金热分析的研究提供了理论基础。利用金属形核与生长过程中固相生长加速度值,可从理论上解释采用TEG,ΔT,ΔTE,t3等作为评估细化及变质结果的热分析判据的原因。
The thermal analysis device developed in this paper is used to quickly determine the microstructure and metamorphism of Al-Si alloy and finish the test in three minutes. The thermal analysis device features: (1) The use of high-precision, multi-function test equipment, it can not only measure the relationship between temperature and time curve, but also test the corresponding differential curve, the absolute temperature error: ΔT ≤ ± 0.3 ℃; (2) a series of experiments on the thermal analysis of the sample cup. The thermal analysis cup structure and material suitable for aluminum-silicon alloy are confirmed, which improves the accuracy and repeatability of the measurement result. In this paper, the effects of Ti, Na, Sb, Sr and Re on the hypoeutectic Al-Si alloy and its influence on the eigenvalues of the thermal analysis curves were systematically investigated. The thermal analysis criteria for evaluating the degree of deterioration of the hypoeutectic Al-Si alloy were obtained. With Na, Sr, Re metamorphism never metamorphosed to good metamorphism, eutectic growth temperature TEG, eutectic nucleation undercooling ΔTE; decreased, eutectic undercooling ΔT showed an increasing trend. When metamorphic with Sb, it never metamorphosed to good metamorphism. The ΔTE and ΔT showed an increasing trend while the TEG showed a decreasing trend. As the Ti content increased, the minimum temperature of α primary nucleus increased and the degree of undercooling decreased. Based on Newton’s heat transfer equation and thermodynamics theory, combined with the thermal analysis curve of Al-Si alloy, the equations of solid fraction, solid-state growth rate and solid-state growth acceleration can be deduced. Research provides the theoretical basis. Utilizing the nucleation of metal and the acceleration of solid phase growth during growth, the reasons for the use of TEG, ΔT, ΔTE, t3 and so on as thermal evaluation criteria for evaluating refinement and metamorphism can be theoretically explained.