Investigation On Microstructure And Properties Of ZrMgMo₃O₁₂ Reinforced Al-40Si Composite

Aiming at some problems existing in traditional aluminum matrix composites,ZrMgMo₃O₁₂reinforced Al-40Si matrix composites(ZrMgMo₃O₁₂/Al-40Si composites)were prepared by powder metallurgy.The preparation process of ZrMgMo₃O₁₂/Al-40Si composites was explored.The effects of ball milling process and ZrMgMo₃O₁₂reinforcement content on the microstructure,mechanical properties and thermophysical properties of ZrMgMo₃O₁₂/Al-40Si composites were systematically studied.The following research results were obtained:1.All the ZrMgMo₃O₁₂/Al-40Si composites prepared at various of sintering temperatures are composed ofα-Al,primary Si and ZrMgMo₃O₁₂reinforcements.The hardness and density of the composites increase with the increase of sintering temperature and sintering time.The composites prepared by sintering at 550℃for 3h have the highest density and hardness,therefore,the preparation process of the composite is determined as holding at 550℃for 3h.2.The increase of ball milling energy is conducive to refining particles of ZrMgMo₃O₁₂reinforcements and primary Si.However,when the milling energy is too high,the high surface energy of ultrafine powders can easily result in the particles reunion of ZrMgMo₃O₁₂/Al-40Si powers and deteriorate the properties of the composites.In addition,high ball milling energy results in a slight chemical reaction between ZrMgMo₃O₁₂andα-Al during hot pressing sintering process,forming a small amount of intermetallic compound Al₁₂Mo.The ZrMgMo₃O₁₂/Al-40Si composites prepared by ball milling at 250rpm for 8h have the best microstructure.3.The addition of ZrMgMo₃O₁₂increases the compressive yield strength of ZrMgMo₃O₁₂/Al-40Si composites,and decreases the coefficient of thermal expansion（CTE）of ZrMgMo₃O₁₂/Al-40Si composites.Ball milling treatment further increases the hardness and compressive yield strength,and decreases the CTE of ZrMgMo₃O₁₂/Al-40Si composites.The composites prepared by ball milling for 8h at250rpm have the highest hardness（148.6HV）,compressive yield strength（430.82MPa）and the lowest CTE(5.8×10^-6/℃).4.The improvement of mechanical properties is mainly attributed to the improvement of microstructure of the composites caused by ball milling treatments enhances the fine grain strengthening effect,the dispersion strengthening effect and the thermal mismatch strengthening effect.The decrease in the CTE of ZrMgMo₃O₁₂/Al-40Si composites is closely related to the increases in the compressive yield strength of ZrMgMo₃O₁₂/Al-40Si composites and deformation resistance ofα-Al matrix.5.The addition of ZrMgMo₃O₁₂will reduce the thermal conductivity of Al-40Si alloy due to its low thermal conductivity.Ball milling processes can further reduce the thermal conductivity of composites,attributing to ball milling treatments increases the interfacial area in the composite,resulting in the increase of heat loss at the interfaces.At the same time,the existence of the interface will also lead to the decreases of phonon and free electron thermal conductivity.6.The content of ZrMgMo₃O₁₂reinforcement influences the microstructure and properties of ZrMgMo₃O₁₂/Al-40Si composites.With the increase of ZrMgMo₃O₁₂content,the hardness and compressive yield strength of the composites increase first and then decrease,while the CTE and thermal conductivity decrease first and then increase.ZrMgMo₃O₁₂/Al-40Si composites with 15wt.%ZrMgMo₃O₁₂have the best mechanical properties,the lowest CTE and thermal conductivity.7.Improving the matching of CTE between ZrMgMo₃O₁₂reinforcement and aluminum alloy matrix and improving the microstructure of composites by ball milling process are the key to improve the mechanical properties and thermal expansion properties of composites.The CTE reduction efficiency of common reinforcements is evaluated according to the normalization parametersαproposed in this study,ZrMgMo₃O₁₂reinforcement has the highest efficiency in decreasing the CTE of Al-40Si alloy compared with other reinforcements whereas ZrMgMo₃O₁₂/Al-40Si composites have the lowest CTE.