Molecular Dynamics Simulations And Experiments Of Relationship Of Al₂O₃ And Hydrogen And Wetting Behavior Of Salt Fluxes For Removing Inclusions In Aluminum Melts

This article is based on molecular dynamics simulations and experimental studies of the relationship of Al2O3and hydrogen in aluminum melts,as well as the molecular dynamics simulations of the wetting behavior of salt fluxes with Al2O3in aluminum melts and salt fluxes with aluminum melts,and the agglomerate test of melting of aluminum scraps in salt fluxes,combined with the salt fluxes phase diagram analysis and the design requirements of the salt fluxes for removing inclusions,designed an salt fluxe for removing inclusions suitable for the reuse of waste aluminum,which was applied to removing inclusions of A356 aluminum alloy melts.The main findings are as follows:(1)The molecular dynamics simulation of the relationship of Al2O3 and hydrogen in the aluminum melt shows that the Al2O3 content and temperature in the aluminum melt have a significant effect on the hydrogen diffusion behavior.The Al2O3content and temperature in the aluminum melt affect the ordering of atoms and the formation of vacancies in the aluminum melt,which affects the accumulation and diffusion behavior of hydrogen.Within a certain range,the higher the content of Al2O3 in the aluminum melt,the higher the extreme value of the first peak of the H-H RDF curve,and the higher the coordination number,the higher the degree of hydrogen accumulation.The higher the temperature in the aluminum melt,the higher the diffusion rate of hydrogen,the corresponding extreme value of the first peak of the H-H RDF curve decreases,the coordination number also decreases,and the degree of hydrogen accumulation is smaller.The vacancy increases the diffusion channel of hydrogen in the aluminum melt on the one hand,and on the other hand,it has a binding effect on hydrogen.Therefore,the effect of the vacancy on the diffusion behavior of hydrogen is the result of the interaction of these two factors.The vacancy formed by molecular dynamics simulation can be considered as similar to the"window"structure in the Al2O3 space structure,which becomes the cause of hydrogen adsorption,hinders hydrogen diffusion,and makes it the basis of the hydrogen pore nucleus.(2)The experimental results of relationship of Al2O3 and hydrogen show that,with the increase of A356 aluminum scrap in the melt of A356 aluminum alloy,the porosity of solidification sample increases,the content of oxidized inclusions increases,and the tensile strength of the sam ple decreases.Oxidation inclusions were found around the pores in the metallographic mor:phology and fracture morphology,which further indicated that the pores were formed on the Al2O3,and the Al2O3 and hydrogen in the aluminum melt was Interdependent and effective.This is consistent with the results of molecular dynamics simulations of the relationship of Al2O3 and hydrogen in aluminum melts.(3)Based on the previous experimental results of this research group,(CaF2+AlF3+Na3AlF6)eutectic component was selected as an auxiliary component,and equimolar NaCl+KCl was used as the basic component.Molecular dynamics simulations was used to analyze the wetting behavior of salt fluxes with Al2O3 in aluminum melts and salt fluxes with aluminum melts under the difference of auxiliary component contents.Molecular dynamics simulations of the wetting behavior of salt fluxes with Al2O3in aluminum melts and salt fluxes with aluminum melts indicate that 15%(CaF2+AlF3+Na3AlF6)eutectic component is used as an auxiliary component of salt fluxes compared to a single fluoride as an auxiliary component,which salt fluxes has the best wettability with Al2O3in the aluminum melt and poor wettability with the aluminum melt.The results of aggregation test of A356 aluminum scraps melting in the salt fluxes further show that the 15%(CaF2+AlF3+Na3AlF6)eutectic component as an auxiliary component of salt fluxes which has the strongest ability to dissolve the surface oxide film of A356 aluminum scrap.(4)This article designed an equimolar NaCl+KCl salt fluxes,equimolar NaCI+KCl(85%)+15CaF2(15%)salt fluxes,equimolar NaCl+KCI(85%)+AlF3(15%)salt fluxes,equimolar NaCl+KCl(85%)+Na3AlF6(15%)salt fluxes and equimolar NaCl+KCI(85%)+Na3AlF6(7.8%)+AlF3(5.7%)+CaF2(1.5%)salt fluxes and applied to removing inclusions of A356 aluminum alloy melts.It shows that the equimolar NaCl+KCl(85%)+Na3AlF6(7.8%)+AlF3(5.7%)+ CaF2(1.5%)salt fluxes is the best of removing inclusions and degassing rate reaches 86.59%.The impurity rejection rate reached 86.42%and the tensile strength reached 183.5 Mpa.Compared with the samples without salt fluxes treatment,the tensile strength increased by 27.79%.This is because the equimolar NaCl+KCl(85%)+Na3AlF6(7.8%)+AIF3(5.7%)+ CaF2(1.5%)salt fluxes is the best wettability of Al2O3 in aluminum melt compared to other salt fluxes.The ability of dissolving alumina is stronger.Therefore,during the test of removing inclusions of A356 aluminum alloy melts,it can effectively absorb and dissolve alumina in the aluminum melt and obtain a relatively pure aluminum alloy melt.This shows that the results of molecular dynamics simulations are of great significance for the design of salt fluxes for removing inclusions.