Variational principles and forecasting models of the contents of Ca and Sr during the A356 melting process
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摘要: Ca和Sr是鑄造鋁硅合金中最有效的變質元素,一般在澆鑄前以中間合金的形式加入.然而在廢雜鋁熔鑄再生工業中,原料中常含有微量的Ca和Sr,預控它們在熔煉過程中的含量變化是它們再利用的前提.本文以工業A356鑄錠為原料,實驗研究了熔煉溫度和保溫時間對Ca和Sr質量分數變化規律的影響.結果表明:Ca和Sr質量分數隨著保溫時間延長均呈Exp3P2規律下降,且隨熔煉溫度升高質量分數下降速率均逐漸提高.根據熱力學和動力學分析可知,在廢雜鋁熔煉再生過程前期主要發生[Ca]和[Sr]與熔體中的氧發生氧化反應生成CaO和SrO,這些氧化物又會與Al2O3反應生成Al2O3·6CaO和Al2O3·SrO,經扒渣操作后Ca和Sr質量分數下降.在熔煉中后期,[Ca]和[Sr]以擴散至熔體表層還原Al2O3的方式使它們的質量分數降低.計算得出在660~740℃熔煉A356合金時Ca和Sr氧化反應的表觀活化能分別為182.6 kJ·mol-1和117.8 kJ·mol-1,兩者均受化學反應過程控制.根據Ca和Sr質量分數的變化規律建立了它們的質量分數預報模型,經生產驗證表明預報誤差均小于10%,可用于預報廢雜鋁熔煉再生過程Ca和Sr的質量分數.Abstract: Ca and Sr are the most effective modification elements in the casting of the Al-Si alloy, and they are usually added before casting when the alloy is in the form of the middle alloy. However, in the aluminum scrap melting regeneration industry, small amounts of Ca and Sr are often contained in the raw materials; as a result, controlling the mechanisms responsible for their contents in the raw aluminum scrap materials is a prerequisite for the reuse of such aluminum scrap during the melting process. This study aims to present the experimental investigation of the influences of the melting temperature and the holding time on the variational principles of the Ca and Sr percentage in an industrial A356 ingot during the melting process. The results indicate that the variations in the mass fractions of Ca and Sr both show Exp3P2 laws that continued decreasing gradually with the holding time and that the change rates of the mass fractions of Ca and Sr both improve with an increase in the melting temperature. Based on thermodynamic and dynamic analysis, the reactions of[Ca] and[Sr] with oxygen in the melt occur and CaO and SrO are produced in the first stage of aluminum scrap melting regeneration process; subsequently, Al2O3·6CaO and Al2O3·SrO are produced by the reactions of CaO and SrO with Al2O3, respectively, before the mass fractions of Ca and Sr finally decrease after slagging. In the middle and later stages of the melting regeneration process, the Ca and Sr percentages are reduced by[Ca] and[Sr] diffusing to the melt surface and then deoxidizing Al2O3. The apparent activation energies of Ca and Sr oxidation reactions calculated at 660~740℃ during the A356 melting process are 182.6 kJ·mol-1 and 117.8 kJ·mol-1, respectively, demonstrating that the both reactions are controlled by the chemical reaction process. The Ca and Sr mass fraction prediction models are established according to their variations and the forecast error is less than 10% by the production verification; thus, both mass fraction prediction models can be used to predict the mass fractions of Ca and Sr in scrap aluminum melting regeneration.
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Key words:
- melting temperature /
- holding time /
- mass fraction /
- variational principles /
- prediction models
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參考文獻
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