Abstract
In this paper, the relationship between the liquid structure and the corresponding solidified microstructure of an Al-Si-Mg-P alloy was studied. Experimental results show that Mg can reduce the phosphorous-modification effect if it was added after adding Al-P alloy. However, when it is added before adding Al-P alloy, Mg has no effect on the phosphorous-modification. It is considered that the difference in liquid structure induced by changing the adding order of Mg should be responsible for the above phenomenon, and was investigated by ab initio molecular dynamics simulation (AIMD). It was believed that the high-active Mg atoms could bond P atoms to form P-Mg clusters and then reduce the modification effect of AlP, when pure Mg was added into the prepared Al-Si-P melt. When the pure Mg was added into Al-Si melt before adding Al-P alloy, the Mg atoms would be first occupied by Si atoms to form Mg-Si clusters, and thus lose the ability to eliminate P-Al clusters which dissolve into melt later, leading to a good phosphorous-modification effect.
Highlights
The structural relationship between the liquid melt and the corresponding solidified alloy has been a long-standing concern and is not very clear
There is no proper Al-Si-Mg diagram that can describe in detail all the phases in Al-12.6Si-1.5Mg alloys, but we can speculate on these phases based on the binary Al-Si and Mg-Si diagrams
Since part of Si atoms was bonded by Mg atoms to form Mg2Si phase, the content of Si which would crystallize as Si phase is less than 12.6%
Summary
The structural relationship between the liquid melt and the corresponding solidified alloy has been a long-standing concern and is not very clear now. In 1927, Levi focused on the correlation between the difference in the liquid melt and its resulting varying performance of solid alloys which have the same composition and underwent the same processing [1]. AlP is a very effective compound to modify primary Si phase [6]. Due to the similar crystal parameters, AlP phase could act as high-efficiency heterogeneous nucleation substrate for the primary Si, resulting in an increase in the number of small Si particles [6,7,8,9,10]. As a high-active element, Mg has the potential to react with P element This reaction may reduce the modification effect of AlP. The ab initio molecular dynamics simulation (AIMD), which is a computational chemistry method based on quantum chemistry, was adopted to calculate the information of clusters in the Al-Si-Mg-P system
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