A356熔炼过程中Ca和Sr质量分数的变化规律及预报模型

Variational principles and forecasting models of the contents of Ca and Sr during the A356 melting process

Ca和Sr是铸造铝硅合金中最有效的变质元素,一般在浇铸前以中间合金的形式加入.然而在废杂铝熔铸再生工业中,原料中常含有微量的Ca和Sr,预控它们在熔炼过程中的含量变化是它们再利用的前提.本文以工业A356铸锭为原料,实验研究了熔炼温度和保温时间对Ca和Sr质量分数变化规律的影响.结果表明：Ca和Sr质量分数随着保温时间延长均呈Exp3P2规律下降,且随熔炼温度升高质量分数下降速率均逐渐提高.根据热力学和动力学分析可知,在废杂铝熔炼再生过程前期主要发生[Ca]和[Sr]与熔体中的氧发生氧化反应生成CaO和SrO,这些氧化物又会与Al2O3反应生成Al2O3·6CaO和Al2O3·SrO,经扒渣操作后Ca和Sr质量分数下降.在熔炼中后期,[Ca]和[Sr]以扩散至熔体表层还原Al2O3的方式使它们的质量分数降低.计算得出在660-740℃熔炼A356合金时Ca和Sr氧化反应的表观活化能分别为182.6 k J·mol^（-1）和117.8 k J·mol^（-1）,两者均受化学反应过程控制.根据Ca和Sr质量分数的变化规律建立了它们的质量分数预报模型,经生产验证表明预报误差均小于10%,可用于预报废杂铝熔炼再生过程Ca和Sr的质量分数.

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 Exp3 P2 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,Al2O3·6 CaO 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 k J·mol-1 and 117. 8 k J·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.