Study On The Effect Of P-Cu Alloy On The Structure And Properties Of Al-25wt.%Mg₂Si Composites Based On First Principles

Al-Mg₂Si composites are particle reinforced aluminum matrix composites,which have the advantages of low density,high specific modulus,high thermal expansion coefficient,good wear resistance and simple preparation process.However,in Al-Mg₂Si composites prepared by traditional melting and casting methods,the primary Mg₂Si grains are coarse and mostly sharp,which will severely split the aluminum matrix structure and greatly reduce the mechanical properties of the composites.At present,the selection of appropriate metamorphic elements for alloying modification of Al-Mg₂Si composites can effectively refine the primary Mg₂Si grains,regulate the morphology and distribution of Mg₂Si grains,and improve the mechanical properties of composites.In this paper,the influence of P-Cu modifier on the microstructure morphology,grain size and mechanical properties of Al-25wt.%Mg₂Si composites was studied by experimental means.The study found that adding P-Cu modifier to the Al-25wt.%Mg₂Si composites not only refines the primary Mg₂Si grains,but also improves the morphology and distribution of the Mg₂Si grains.When the added amount of P-Cu modifier reaches about 2.8wt.%,the fineness and morphology control effect of the primary Mg₂Si grains are optimal,and the mechanical properties of the composites are also significantly improved.First-principles calculations based on density functional theory can predict the state and properties of the microscopic system from the atomic or electronic scale without relying on any empirical parameters,so as to realize the optimization and design of materials.In this paper,the second phase strengthening mechanism of Al-Mg-Si-P-Cu alloy relative to matrix structure and the influence mechanism of P and Cu metamorphism elements on the solution strengthening,heteronucleation and morphology control of the strengthening phase Mg₂Si have been studied by first principles calculation method.It is found that Mg₂Si,Al P,Mg₃P₂and Al₂Cu Mg belong to the brittle phase,and Al₂Cu belongs to the ductile phase.Al₂Cu has the best thermodynamic stability and mechanical properties,and can be used as the second phase particles to strengthen Al-25wt.%Mg₂Si composites.The Al P compound has the best alloying ability and good thermodynamic stability,and can be used as the nucleation core of Mg₂Si to refine Mg₂Si grain.Secondly,through the calculation of the interface binding energy and the electronic structure analysis of the Al P(100)//Mg₂Si(211)interface,the study found that the bonding strength of the P terminal Al P(100)//Mg₂Si(211)interface structure is higher than that of the Al terminal Al P(100)//Mg₂Si(211)interface structure.Finally,this paper used first-principles calculation methods to study the influence of the solid solution doping behavior of P and Cu elements on the stability and mechanical properties of the Mg₂Si phase,and the effect on the anisotropy of Mg₂Si(100)and(111)crystal planes.The results show that the solid solution doping behavior of P and Cu elements improves the stability,plasticity and toughness of the Mg₂Si intermetallic compound.The surface doping behavior reduces the anisotropy of Mg₂Si(100)and(111)crystal planes,so that Mg₂Si crystals tend to exist in the matrix in the form of cut-angle octahedrons with(111)and(100)crystal planes coexisting.