The Effect Of Micro-nano ZnS On The Solidification Structure Of Al-Si Alloy

As a light alloy with good casting properties,aluminum-silicon cast alloys have been extensively used in automobile industry,aerospace and electronic packaging owing to their many advantages such as thermal expansion,good wear resistance,high specific strength,which can help meet energy conservation requirements and reduce emissions to satisfy the performance requirement.However,due to the high Si content of Al-Si alloys,a large amount of long,coarse needle-like eutectic Si and coarse bulk primary Si in the microstructure can seriously dissever the matrix and adversely affect the mechanical properties of the alloy.Therefore,in recent years,researchers have mainly focused on the refining of primary Si and eutectic Si in Al-Si cast alloys to improve the overall properties of the Al-Si cast alloy.In this paper,the effect of ZnS on the solidification structure of hypereutectic Al-24 Si cast alloy and eutectic Al-12 Si cast alloy were studied:(1)Adopting the additive method and the in-situ generation method,the hypereutectic Al-24 Si alloys were modified using ZnS.The primary Si and eutectic Si in hypereutectic Al-24 Si alloy have been refined.Comparing the in-situ generation method with the additive method,it is found that when 0.6% of micro-nano ZnS was added to the alloy by the additive method,the primary Si in the hypereutectic Al-24 Si alloy has been grately refined,and the average size is 23.46?m,the size distribution range of primary Si is narrow.(2)The Al-12Si/ZnS modifier was prepared by a simple chemical water bath deposition method,and its phase and morphology were analyzed by XRD,SEM,TEM and EDX.The size and morphology of eutectic Si in the Al-12 Si alloy was modified by the addition of Al-12Si/ZnS powder.The best refinement effect for needle-like eutectic Si was achieved in the Al-12 Si cast alloy with 17.5%Al-12Si/ZnS powder.Eutectic Si is modified into a coral-like spherical shape with the average size of about 6.53 ?m.The hardness,tensile strength and elongation of Al-12 Si alloys modified with 17.5% Al-12Si/ZnS powder increased by 6.3%,16.19 and 55.35%,respectively,compared to the non-modified Al-12 Si alloy.Fracture behavior was dominated by transgranular fracture supplemented by intergranular fracture.(3)According to the principle of thermal analysis,an aluminum-silicon(Al-Si)-based cast alloys thermal analysis instrument was designed and installed,and the cooling curve of Al-Si based cast alloys with and without modification were measured and analyzed.It was found that the degree of subcooling for the crystallization of primary Si and eutectic Si were reduced by adding ZnS modifier.The subcooling degree for the crystallization of primary Si in hypereutectic Al-24 Si alloy with 0.6% nano ZnS increased by 56.2?;the subcooling degree for the crystallization of eutectic Si in eutectic Al-12 Si alloy with 17.5%Al-12Si/ZnS increased by 23.2?.