Effect Of Sb On Microstructure And Mechanical Properties Of ZL114A Alloys

As a high-strength casting Al-Si alloy independently developed in China,ZL114A alloy is widely used in the fields of aerospace and automobile industry due to its superior casting property,fluidity and processability.With the development and progress of industrial technology,higher requirements have been put forward for the strength and toughness of ZL114A alloy.In this paper,ZL114A alloy was taken as the research object,and the effect of Sb on the microstructure and mechanical properties of ZL114A alloy at different cooling rates was studied by OM,SEM,EDS,EBSD,TEM and room temperature mechanical properties detection,and the mechanism of Sb element on the primary?-Al dendrite and eutectic silicon of the alloy was analyzed.(1)The microstructure and mechanical properties of ZL114A alloy with different Sb content were studied.The addition of trace Sb element would significantly affect the primary?-Al dendrite and eutectic silicon morphology of ZL114A alloy.In the solidification process,because the distribution coefficient of Sb in Al is very small,it is easy to accumulate in the solid-liquid interface leading to the composition of supercooling,which increases the instability of the solid-liquid interface,leading to the growth of the primary?-Al dendrite of the alloy,the narrowing and lengthening of the secondary dendrite,and the decreasing of the secondary dendrite arm spacing.After Sb modification,the eutectic silicon of the alloy decreased in size,and the average eutectic silicon width of the unmodified alloy was 5.4?m;after 0.19wt%Sb metamorphism,the average eutectic silicon width of the alloy decreased to 2?m,and its morphology changed from unmodified lamellar to short bar shape.The eutectic silicon containing 0.19wt%Sb alloy had the best modification effect.At this time,the tensile strength,yield strength,elongation and reduction of section of the alloy were328.1MPa,234.2MPa,8.5%and 10.5%,respectively.(2)The microstructure and mechanical properties of base alloys and alloys containing 0.19wt%Sb at different cooling rates were studied.The results show that with the increase of cooling rate,the primary?-Al dendrite in ZL114A alloy were further refined,and the metamorphic effect of eutectic silicon was significantly enhanced.When the cooling rates reached 7.42?/s,the average width of the eutectic silicon of the base alloy was 4.13?m,and the average width of the eutectic silicon of the alloy containing 0.19wt%Sb was 1.13?m,respectively.At this time,the comprehensive mechanical properties of the alloy were the best.The tensile strength,yield strength and elongation of the alloy were 351MPa,253MPa and 17.9%,respectively.The increase of cooling rate and the addition of Sb will result in the decrease of eutectic reaction temperature of the alloy,in Sb metamorphic alloy,the eutectic reaction temperature has a good linear relationship with the cooling rate.The sensitivity of eutectic reaction temperature to cooling rate of unmodified alloy decreases with the increase of cooling rate,because eutectic silicon grows faster at high cooling rate and releases a lot of latent crystallization heat.(3)The modification mechanism of Sb on eutectic silicon was studied,and the effect of Sb on the nucleation and growth of eutectic silicon was analyzed.Sb modification was not realized by direct adsorption on the growth step of eutectic silicon but by reacting with Mg in the alloy to form Mg₃Sb₂ phase,Mg₃Sb₂ phase poison the heterogeneous nucleation particle Al P of eutectic silicon,resulting in the increase of eutectic silicon nucleation supercooling degree and inhibiting the growth of eutectic silicon.In the unmodified alloy,most eutectic silicon is directly nucleated on the surrounding primary?-Al.After Sb modification,the nucleation mode of eutectic silicon is transformed into nucleation growth in the inter dendritic fluid.The higher the cooling rate is,the more obvious this phenomenon is.