Design And Preparation And Property Study Of High Strength And Toughness Of Al-Si-Mg-Mn For Automobile

With the low relative density,high specific strength,ease of processing and abundant resource reserves,aluminum alloys are widely used in automotive to replace conventional steel.In this work,the composition of the alloy was optimized from conventional Al-Si alloy by literature search and thermodynamic calculations of phase diagrams.The effects of refining times,melting times and heat treatment on the composition,structure and mechanical properties of the alloy were investigated.The good toughness and strength cast Al-Si alloy and high strength T6 treated Al-Si alloy were obtained.Meanwhile,by comparing the on-plane projection of 3D orientations of grains revealed by EBSD and in-situ SEM observations of Si particles during deformation,the relative rotation of Si particles and its effect on the mechanical property were investigated.All findings are concluded as follows:(1)According to the current market demand,literature research and phase diagram calculation,the new alloy composition was designed as Al-8Si-0.2Fe-(0.25-0.30)Mn-(0.3-0.4)Mg-0.1Ti-0.02B-0.02 Sr.Increased refinements times can effectively reduce oxidation inclusions and porosity during the casting process.Increased the melting times can increase the Fe content of the melt and reduce the Sr and Mg contents.However,there is no significant effect on grain size during the change of melting time.Under the same die-casting conditions,the trapped gas is more serious in the flake tensile samples than the rod tensile samples.Therefore,the elongation of the former is lower.However,the yield strength of the former is higher because its solidification structure is finer.The tensile strength of the as-cast sample is 292.53 ± 8.15 MPa,the yield strength is 145.48 ± 9.82 MPa,and the elongation is 7.77 ± 1.01 %.The tensile strength of the T6 heat-treated sample is 311.80 ± 19.20 MPa,the yield strength is 203.98 ± 29.53 MPa,and the elongation is 6.42 ± 1.96 %.The yield strength of the T6 treated sample was increased by 40%,the elongation was reduced by 17%.(2)During tensile deformation of the Al-Si alloy,fine sub-micron Si particles were found to be rotated obviously with respect to α-Al matrix grains.Moreover,(geometrically necessary dislocations)GNDs can be generated in the matrix near the Si particles due to the relative rotation between them.The stronger the relative rotation,the higher the GND density.A high density of GNDs can cause larger work-hardening effects.When the particles were broken or deboned with the matrix,the GNDs and corresponding work-hardening effect would be released at the defect.However,new defects would be introduced at this time,which will become the source of crack nucleation and reduce the mechanical properties in the next tensile process.