Microstructure And Mechanical Properties Of HEAp/AlSi12 Composites Prepared By Powder Metallurgy

Particle reinforced aluminum matrix composites have excellent properties such as high specific strength,high specific modulus,high wear resistance and good dimensional stability.However,the plasticity and toughness of traditional aluminum matrix composites reinforced by ceramic particles are poor,which limits their application in structural materials.Therefore,how to improve the strength of composites while ensuring good plasticity and toughness has always been the goal of researchers.With the appearance of high entropy alloy,its unique microstructure and characteristics make high entropy alloy have the characteristics of strength and toughness,wear resistance and corrosion resistance,which are potentially superior to traditional metals.The interfacial wettability and interfacial compatibility of high entropy alloy and aluminum alloy matrix are good.Therefore,in this paper,high entropy alloy particles are used as reinforcement system to prepare particle reinforced aluminum matrix composites,which is expected to break through the bottleneck of traditional ceramic reinforcement and toughening and realize the possibility of improving the strength and toughness of composites simultaneously.In this paper,HEAp（AlCoCrFeNi）/Al Si12 composite material is prepared by two processes using powder metallurgy.The effects of sintering temperature and HEAp volume fraction on the microstructure of composites were investigated by scanning electron microscopy（SEM）,X-ray diffraction（XRD）and transmission electron microscopy（TEM）.The hardness and tensile strength of composites were detected by Vickers hardness tester and tensile test machine,the mechanism of HEAp and Al Si12were analyzed,and the strengthening mechanism of HEAp/Al Si12 composites was discussed.The results are as follows:In the composites prepared by hot extrusion sintering at 450℃（HEA stable temperature）,the HEAp is evenly distributed in Al Si12,and the interface is well combined with Al matrix,without microgap and inclusion.There are tens of nanometers of element diffusion at the interface,but there are no obvious reaction products and reaction layer formation.The average grain size of Al grain decreases with the increase of HEA grain volume fraction.The hardness,yield strength,tensile strength and elongation of the composites with HEA particles were improved compared with those without.From the microscopic morphology of the fracture,it can be seen that the fracture is ductile and brittle mixed fracture mode.In the aspect of strengthening of composite materials by introducing HEA,fine grain strengthening plays a major role.After comprehensive analysis,HEAp/Al Si12 composite with HEA volume fraction of7%has better comprehensive performance.In the HEAp/Al Si12 composites prepared by high temperature sintering（HEA unstable temperature）at 550℃and hot extrusion at 480℃,Al diffuses into HEA,forming Al₄₅M₇ phase in the inner side of the interface.Atoms near the interface of HEA enter into Al matrix,forming Al₉M₂ phase in the outer side of the interface.With a long time of heat preservation,the interfacial reaction intensifies,and the enhancement region appears obvious amplification and forms two morphologies,which are mainly composed of Al₉M₂ and Al₄₅M₇,respectively.With the change of initial HEA addition amount,the proportion of the two morphologies in the reinforcement region will change.Moreover,when the volume fraction reaches a certain value,Cr and Al elements in the sample react with Si elements to generate Al₁₃Cr₄Si₄ small particle phase,which is distributed around the enhanced area.The interfacial reaction between HEA and Al intensifies at higher sintering temperature.With the introduction of intermetallic compounds into the interfacial reaction,the hardness of composites increases significantly,while the plasticity decreases sharply.