Thermal Analysis On Modification Effect Of Hypoeutectic Aluminum-silicon Alloys With Antimony

Al-Si alloy,which has the advantages of low density,good wear resistance and so on,is widely used in the fields of automobile,rail transportation,household appliance industry.The modification treatment of hypoeutectic Al-Si alloys is often used to ameliorate the eutectic morphology and improve the mechanical properties.Thermal analysis?TA?technology is one of the advanced methods for rapid detection of melt quality before casting.In this paper,the aluminum alloy thermal analysis software was programmed firstly with LabVIEW language.Then,the modification effect of Sb on Al-Si alloys was studied using this software.The TA software was provided with temperature-time data acquisition,data handling,first order differential,automatic identification of characteristic values and print fuction.ZL101 and ZL104,as typical hypoeutectic Al-Si alloys,were studied by means of thermal analysis in this paper.The modification effect for the alloy with different antimony?Sb?addition and holding time was studied.The results of thermal analysis showed that,the addition of Sb exalted the primary crystal platform,declined the eutectic platform,and there was a significant eutectic recalescence in cooling curves of both kinds of alloys.When the characteristic values?T_EG>7°C,better modification effect of Sb on the ZL101 alloy can be achieved.Sb had little effect on primary?-Al crystal microstructure,but eutectic Si phase began to be refined under slower cooling rate at 0.9°C/s.With increasing the amount of Sb,the size of Si acicular decreased gradually in both width and length direction.While cooling at 33°C/s,the modification effect was greatly enhanced,the morphology of eutectic Si phase exhibited slender rod or even nearly granular shape.On the whole,the optimum additions of Sb were0.2 wt.%and 0.4 wt.%for ZL101 and ZL104 alloys respectively.As holding time prolonged,the modification effect of ZL101 alloy exhibited the trend of promotion,but it had negligible impact on ZL104 alloy.The eutectic nucleation temperature T_EN reduced with the addition of Sb,it proved that Sb can retrain the nucleation of eutectic Si to a certain extent.During solidification process,high melting point compound Mg₃Sb₂ precipitated firstly,and then affected the solute redistribution,eutectic Si phase achieved refinement in the larger undercooling.Rapid cooling rate changed the interface structure,tended to form a short rod-like morphology in faster growth velocity.The as-cast tensile strength of the unmodified ZL101 alloy is 207.7MPa,the elongation is 2.53%,the performance of modified alloy is improved firstly and then deteriorated.The optimum value is obtained when adding 0.2 wt.%Sb,which reaches at 237.1MPa and 8.38%,respectively.It increased by 14.12%and 231%respectively compared with the unmodified alloy.After T6 heat treatment,the tensile strength of unmodified alloy is 290.4MPa,which is nearly 40%higher than that as-cast alloy.However,the promotion amplitude of T6-treated properties contrast to as-cast alloy reduced with the increase of Sb addition.T6 heat treatment can fuse the eutectic silicon and convert it to spherical phase,the decline of the mechanical properties is due to Sb consumption of Mg alloy in the alloy,reducing the precipitation of dispersion strengthening phase Mg₂Si.