The Effect of Mg Adding Order on the Liquid Structure and Solidified Microstructure of the Al-Si-Mg-P Alloy: An Experiment and ab Initio Study

Abstract

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.

Alloy development and reheating process exploration of Al–Si casting alloys with globular grains for thixoforming

“…The most distinct characteristic of thixoformed microstructure is the co-existence of liquid and solid during processing (since this occurs at semi-solid temperatures), and the formation of a primary phase with near-spherical grain morphology [9][10][11]. This process has received considerable attention recently due to its significant advantages over traditional metal forming process, such as minimization of as-cast porosity and macrosegregation; reduced forming temperatures, forming forces, and machining costs; and high strength and corrosion resistance [12][13][14][15].…”

Some Issues in Liquid Metals Research

“…In [6], thermodynamic calculations are carried out to identify the regions of the ternary phase diagram of Al-Cu-Y, where the formation of amorphous alloys is most probable. Experimental data and ab initio calculations are presented in [7] to show that an optimal microstructure is obtained if Mg is added to the Al-Si melt before than the modifier AlP alloy. Shock-induced melting of metals by means of laser driven compression is discussed in [8].…”

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The ten articles [1][2][3][4][5][6][7][8][9][10] included in this Special Issue on "Liquid Metals" do not intend to comprehensively cover this extensive field, but, rather, to highlight recent discoveries that have greatly broadened the scope of technological applications of these materials. Improvements in understanding the physics of liquid metals are, to a large extent, due to the powerful theoretical tools in the hands of scientists, either semi-empirical [1,5,6] or ab initio (molecular dynamics, see [7]).

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“…In order to modify this microstructure, several elements and/or alloys are added to the melt that during the solidification process modify the acicular eutectic to a less detrimental globular eutectic acting also as a high-efficiency heterogeneous nucleation substrate for the primary Si so reducing their size. Zhu et al [7] consider the performance of AlP alloy as a modifier addressing the important technological problem of whether the order in which Mg and AlP are added to the melt matters. Extensive experimental studies and numerical calculations by means of ab initio molecular dynamics simulations allow the authors to conclude: (a) when pure Mg is added to the Al-Si melt before the Al-P alloy, Mg-Si clusters form that coexist with P-Al clusters.…”

“…Improvements in understanding the physics of liquid metals are, to a large extent, due to the powerful theoretical tools in the hands of scientists, either semi-empirical [1,5,6] or ab initio (molecular dynamics, see [7]). Surface tension and wetting at metal/ceramic interfaces is an everlasting field of fundamental research with important technological implications.…”