Study On Integration Processing Of Grain Refinement And Eutectic Modification In Al-Si Alloys

In this work,Sb was used as modifier to first investigate its modification effect on Al-7Si alloy.Microstructure observations showed that addition of 0.4% Sb was suffiect to achieve a fully modified eutectic structure,the mean are and aspect ratio of eutectic Si particles were reduced remarkably.Tensile tests showed that the mechanical properties especially elongation of A356 alloy were largely improved by addition of Sb.It can be conclude that Sb can be used as an effective modifier for Al-Si alloys.The interaction between Sb and Al-5Ti-1B/Al-3B in Al-7Si alloys were investigated,and the grain refinement effects of Al-5Ti-1B and Al-3B mster alloys were compared.Results indicated that there was an “poison effect” between Al-5Ti-1B and Sb in Al-Si alloy,therefore the grain refinement and modification effects were depreesed.while that there was no “poison effect” between Al-3B and Sb in Al-7Si alloy which means that the addition of Al-3B and Sb in Al-7Si alloys can fullfil excellent grain refinement and eutectic modification.The grain refinement results show that Al-3B had a better grain refinement effect than that of Al-5Ti-1B master alloy.Al-10Sb-1B master alloy was prepared by flux-covered reaction method and it is used to fulfill an integration processing of grain refinement and eutectic modification in Al-Si alloys.The master alloy thus prepared has a clear matrix and uniformly distributed second phase.The second phase is comproised of AlSb phase acting as modifier and AlB2 particles acting as heterogeneous nucleation sites.The grian refinement and eutectic modification effects of Al-10Sb-1B master alloys on Al-7Si alloy were investigated.Results showed that Al-10Sb-1B master alloy was able to reduce the grain size of Al-7Si alloy to less than 200?m and to transfer the coarse plate-like eutectic Si phase into fine fibrous structure.The mechanical properties of Al-10Sb-1B treated A356 alloy were also investigated.Tensile tests showed that by addition of Al-10Sb-1B master alloy,the tensile strength of A356 alloy reached 194 MPa and the elongation reched 12.1%.The grain refinement and modification mechanisms were investigated respecticely.Results showed that AlB2 had a great crystallographic matching with Al matrix,therefore,AlB2 appeares to be an efficient substrate for nucleating ?-Al;the nucleation temperature and frequency were depressed by Sb and this is probably attributable to the formation of AlSiSb phase which consume the free-P mostly during holding before solidification.