Development Of Al-Mn Master Alloy And Its Effect On Al-15Si Alloy Structures

The final mechanical properties and performances of materials depend on their microstructure.Specific melts treatment is often used to obtain high-quality materials for industrial application.Al-Si alloy is one of the most widely used aluminum alloys by virtue of its excellent performance.With the increasing demanding for Al-Si alloys,the standard of qualities has also been continuously improved.A variety of treatments have been developed to regulate the internal microstructure of Al-Si alloys.For hypereutectic Al-Si alloys,the coarse primary Si phase can seriously deteriorate the comprehensive mechanical properties of the materials.Specific master alloys adding to the melt can control the morphology of the Si phase,which is the most effective melts treatment method in industry at present.The inoculating mechanism of most master alloys is to introduce heterogeneous nucleation substrates into the melt to refine Si phase.In this paper,we employ a new AI-Mn master alloy,and its inoculating effects on the nucleation and growth of Si phase in Al-15Si were investigated through systematic experiments.The microstructure and solidification behavior of Al-Mn master alloy were characterized by XRD,SEM and DSC.And structure factors of Al-Mn system were simulated by first-principle molecular dynamics calculation software VASP.It was found that local ordering(AIMn)clusters will appear in the melt along with the melting of Al-Mn master alloy in the heating process.The refinement effects of Al-Mn master alloy on Si phase in Al-15Si were studied by numerous systematic experiments and the optimal inoculation parameter was determined.The optimal parameter is verified to be 1%inoculant addition holding 30 min,the average size of primary Si decreases from?110?m to?20?m,and the morphology is more regular.It is found that inoculating mechanism of Al-Mn master alloy is different from that of traditional heterogeneous nucleants through investigation of cooling curves and contrast experiments.Combining the discovery of high density nanoscale particles in HRTEM images,cluster-assisted crystallization mechanism was proposed.The appearance of nanoscale particles is directly related to the presence of(AlMn)clusters in Al-Si melt,pre-nucleation clusters can be induced by(AlMn)clusters to increase nucleation.The effects of complex modification by Al-Mn master alloy and Sr modifier on Al-15Si were further studied.Eutectic Si transforms from sharp plate-like to dense coralline in Al-15Si by complex modification,and the size of the primary Si is also clearly controlled.The tensile properties of the material was elevated to a higher level.The optimal parameter of complex modification treatment for Al-15Si:modified by Sr modifier and held for 10min and then inoculated by 1%Al-Mn master alloy for 30min.