Effect Of Super Gravity Field And Modification On Eutectic Microstructures And Properties Of Al-Si Alloy

In this paper,the effects of super gravity field combined with eutectic Si modifier on the refinement of eutectic Si,the point shift of eutectic composition and mechanical properties of Al-Si alloy were investigated.Firstly,taking Al-12 wt.% Si alloy with more eutectic structure as the research object,The refining effect of super gravity field combined with different modifiers on eutectic Si in alloy structure was studied.After finding the modifier with the best synergistic refining effect,the synergistic effect of the super gravity field and the modifier was used as a new composite method for refining eutectic silicon,and its effect on the the displacement of eutectic composition on Al-Si alloy was mainly investigated.Finally,under the pseudoeutectic composition,we change the super gravity coefficient to explore the optimal super gravity size for the synergistic refining effect.The results of refining eutectic Si of Al-12 wt.% Si alloy by the combined treatment of super gravity field at 3000 g and different modifiers show that there is obvious macrosegregation in the alloy under the combined action.The microstructure of the alloy consists of two parts: the hypoeutectic zone at the edge and the eutectic zone at the center.The synergistic effect is better than that of pure super gravity or modification.Among them,the synergistic effect of super gravity field and sodium salt modification is the best.At this time,eutectic Si in the center of ingot appears as short rod,with an average length of about 0.39?m and an average diameter of about 0.22?m.The synergistic effect on the hardness of the alloy core is also more obvious.The highest hardness of the ingot core is 88 HV when treated by the combination of super gravity field and sodium salt modification.The results of super gravity field migration of eutectic composition of Al-Si alloy modified by sodium salt show that the eutectic composition of Al-Si alloy modified by sodium salt shifts to the right when solidified under 3000 g super gravity field.When the content of Si is 14.5wt.%,there is no primary Si in the alloy structure.At this time,the area of eutectic zone in the center of the alloy accounts for more than 40%.The length,diameter and hardness of eutectic Si in the heart are 0.47 um,0.25 um and 87 HV respectively.The results of the solidification structure and mechanical properties of Al-14.5Si alloy modified by sodium salt under super gravity field show that the refining degree of eutectic Si in the center of the alloy increases with the increase of gravity coefficient before G=2000g,and the size of eutectic Si in the center of the alloy does not change much after 2000 g.The synergistic effect of high gravity field and sodium salt modification can significantly improve the mechanical properties,especially elongation,from 1.3% at normal gravity to 12.7% at 4000 g.When G = 3000 g,the tensile strength,yield strength and core hardness of the alloy reach their maximum values,which are 224 MPa,111MPa and 87 HV,respectively,and increase 73.6%,22% and 34% respectively compared with those under normal gravity.