Study On Preparation And Properties Of Mg₂Si/ZA40 Composites

The Mg₂Si/ZA40 composites were fabricated by in-situ gravity casting method. The effects of antimony modification and reinforcing phase Mg₂ Si contents on the microstructure and properties of the composite materials were studied Several analysis and detection methods, such as tensile test, impact test, hardness test and density testing, were used by optical microscopy, scanning electron microscopy and X-ray diffraction?XRD?. The main conclusions are as follows.The Mg₂Si/ZA40 composites with different Mg₂ Si contents?3%, 6%, 9% and 12%? were fabricated by gravity casting method with antimony as modifier, by adding the aluminum-silicon master alloy and pure magnesium into the liquid of ZA40 alloy. Then the microstructure of the composite got compact and distributed more uniformlyAfter antimony modification, the microstructures of the composites were improved. The morphology of the primary Mg₂ Si particles of composites has been changed from coarse cross or irregular shape to a polygonal lumps and even to small particles, and its dimension has greatly reduced and the distribution becomes more uniform; the grain of matrix alloy has also been corresponding refined, the secondary dendrite arm spacing has reduce and the organization is more compact. The optimal parameter of antimony modification on ZA40-9%Mg₂Si composites is 720 degrees for the modification temperature, 20 min for the modification time and 0.9% for the addition amount.The hardness, tensile strength, elongation and impact toughness of antimony modified Mg₂Si/ZA40 composites were increased by 6.5%, 3.6%, 25.7% and 11.9% respectively, compared with the composites without-modification. With the addition of Mg₂ Si contents, the hardness of the composites increases gradually, and the impact toughness and the elongation decreases gradually. The tensile strength decreases slightly as the addition of Mg₂ Si contents increases when contents is less than 6wt%, while the tensile strength decreased obviously when contents is more than 9wt%. The tensile strength of the composites began to decrease slightly and then decreased obviously.The wear resistance of the composites surpasses the matrix ZA40 alloy. Under the lubrication condition, when the load is 500 N, the wear loss of the composite with 9%Mg₂Si particles decreased by 22% compared with matrix alloy; when the load is 700 N it reduced by 21.3%. Under the condition of dry friction and load of 200 N, the wear loss of the composite with 9%Mg₂Si particles dropped by 19.5%, and when the loading is 250 N it reduced by 321.8%. The friction and wear test results showed that the adhesive wear was the dominant in matrix alloys, while the wear mechanism of Mg₂Si/ZA40 composites was the comprehensive result caused by adhesive wear and abrasive wear.