Study On Microstructers And Properties Of In-situ Mg₂Si/ZA40 Composites

In this paper,in-situ Mg₂Si/ZA40 composites were fabricated by gravity casting and liquid forging process.The microstructure,fracture morphology,wear surface and phase composites of the alloys were studied by using X-ray diffraction,scamming electronical microscope,and optical microscope,respectively.The mechanial properties of the composites,such as tensile strength,elongation,hardness,impact toughness and wear resistance were studied by tensile test,hardness test,impact test and wear test,respectively.This study draws the main conclusions as follows:The Mg₂Si/ZA40 composites were fabricated by gravity casting and liquid forging method with antimony as modifier.By adding the aluminum silicon master alloy and pure magnesium into the liquid of ZA40 alloy,four kinds of the composites were fabricated,and their Mg₂ Si contents were 3%,6%,9%,12%,respectively.The microstructure of the composites were greatly improved after antimony modification.For gravity casting 9%Mg₂Si/ZA40 composites,the modification temperature 720?,the modification time was 20 minutes and the modifer amount was 0.9wt%.The hardness,tensile strength,elongation and impact toughness of antimony modified Mg₂Si/ZA40 composites were increased by 6.5%,3.5%,7.7% and 12% respectively,compared with no modification.When the pouring temperature,the loading and holding time were fixed to720?,140 KN,and 10 s,respectively in liquid extrusion process,the hardness,tensile strength,impact toughness,elongation and wear resistance of Mg₂Si/ZA40 composites prepared by liquid extrusion had improved by 7%,6.7%,7%,24% and 18%.Comparing with the composites by gravity casting.The dry friction coefficient of composite material decrease with the increase of the Mg₂ Si content.The friction coefficient decrease from 0.483 of ZA40 to 0.393 of 9%Mg₂Si/ZA40 composite.The wear resistance of Mg₂Si/ZA40 composites was investigated under the conditions of dry friction and oily lubrication.The results show that the wear resistance of the composites was better than that of the matrix materials and the wear resistance increased when the applied load increased.Moreover,the composite materials seriously worn under the condition of dry friction,which indicates that Mg₂Si/ZA40 composites were not suitable for dry friction.The wear resistance was studied by comparing the 9%Mg₂Si/ZA40 composites with tin bronze.The experiment resuls show that the wear resistance of the composites was superior to the tin bronze.The wear resistance of the composites was better than the tin bronze in overload conditions.Thus,the 9%Mg₂Si/ZA40 composite has a wider scope of application.