THERMOPHYSICAL PROPERTIES OF HYPOEUTECTIC, EUTECTIC AND HYPEREUTECTIC Al-Si AUTOMOTIVE ALLOYS UNDER AGEING TREATMENT

Q3 Engineering
Ahmed Asif Razin, Dewan Sal-Sabil Ahammed, A. Khan, Mohammad Salim Kaiser
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Abstract

Influence of different levels of silicon under a variety of thermal treatment is investigated on the thermophysical behaviour of Al-Si-Cu-Mg automotive alloys. Conventional cast alloys are subjected to T6 heat treatment for age hardening. Hardness values, thermal conductivity along with microstructural observation under different heat-treated conditions are well thought-out to comprehend the ageing performance and the precipitation behaviour of the alloys. From these investigational results it is indicated that two successive hardening peaks take place in the agedalloys. Ageing sequence consists of different phases like a supersaturated solid solution, GP zones, intermediate βʹʹ, intermetallic βʹ, equilibrium β and the Q phase but GP zones and the metastable phases are most likely responsible for these ageing peaks. Thermal conductivity decreases for these precipitates formation during ageing and increases for relieving the internal stress, dissolution of metastable phase and coarsening the precipitation of the alloys. Addingup of Si to the alloy showed earlier ageing peaks with higher intensities intended for its increasing properties of heterogeneous nucleation and diffusion kinetics. After ageing around at 200°C for four hours the alloys offer the height hardness. Microstructural study reveals that eutectic silicon makes the grain boundary coarsen and beyond the eutectic composition the star-shaped blocky primary Si is formed. Subsequent to ageing at 350oC for one hour the alloys reach completely recrystallized state.
老化处理下的氢化、电解和热解铝硅合金的热物理特性
研究了在各种热处理条件下不同含量的硅对铝-硅-铜-镁汽车合金热物理特性的影响。传统的铸造合金经过 T6 热处理进行时效硬化。通过对不同热处理条件下的硬度值、热导率以及微观结构的观察,可以很好地理解合金的时效性能和析出行为。这些研究结果表明,在老化合金中会出现两个连续的硬化峰值。老化序列由不同的相组成,如过饱和固溶体、GP 区、中间 βʹʹ、金属间 βʹ、平衡 β 和 Q 相,但 GP 区和析出相最有可能造成这些老化峰。这些析出物在老化过程中形成时,热导率会降低,而在消除内应力、溶解析出物和粗化合金析出物时,热导率会升高。在合金中添加硅会出现更早的老化峰,且强度更高,这是因为硅会增加异质成核和扩散动力学的特性。在 200°C 左右的温度下老化四小时后,合金的硬度有所提高。微观结构研究表明,共晶硅会使晶界变粗,在共晶成分之外会形成星形块状原生硅。在 350 摄氏度老化一小时后,合金达到完全再结晶状态。
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来源期刊
Journal of Chemical Technology and Metallurgy
Journal of Chemical Technology and Metallurgy Engineering-Industrial and Manufacturing Engineering
CiteScore
1.40
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