Study On The Effect Of Zr And Y On Microstructure And Properties Of Al-Si-Al₂O₃ Composites

The dense Al-Si-Al₂O₃ composites were prepared by hot isostatic pressing with the in-situ reaction method.Reference modification treatment was commonly used in casting Al-Si alloys.According to the characteristics of powder metallurgy,the aluminum matrix composites were prepared by using the thermostatic in-situ synthesis technology to refine the grain and improve the characteristics of the structure,and improve the performance of composite materials.Selecting micron aluminum powder,ZrH₂ powder and YH₂ powder,as well as nano-SiO₂powder as raw materials,using hot isostatic pressing sintering technology,and successfully prepared the Al-Si-Al₂O₃ composites:Al-5wt.%Si-Al₂O₃?Al-5wt.%Si-Al₂O₃-Zr?1.0wt.%?1.5wt.%?2.5wt.%??Al-5wt.%Si-Al₂O₃-Y?0.5wt.%?1.0wt.%?1.5wt.%?,were successfully in-situ synthesized from Al and SiO₂ powders under hot isostatic pressing.X-ray diffraction analysis,optical microscopy,scanning electron microscopy and transmission electron microscopy were used to analysis microstructures,and phases of composites.The influences of additive modificator on the mechanical properties were detail tested by tensile,shear,and compression tests.XRD analysis showed that Al,Si and Al₂O₃ phases were detected in the material,in-itu reaction is complete,the relative density is over 99%before and after adding Zr.The second phase Al₃Zr and ZrSi₂ appeared after the addition of the metamorphic agent Zr,and the second phase YAl₂Si₂ appeared after the addition of the metamorphic agent Y.The size of silicon particles in the optical microstructure of the modified Zr and Y were significantly reduced,but there were more pores in the aluminium-silicon alloy composites containing the metamorphic agent Y.The density of composites is more than 97%.TEM showed the microcosmic state with the additive of Zr?Al-5wt.%Si-Al₂O₃-2.5wt.%Zr?is mainly composed of Al matrix composite material?Al₂O₃ in substrate?with a large number of the seconed phase?strip?of small multilateral shape and large beam structure?Al₃Zr and ZrSi₂?,the diffraction spot also proved the existence of the second phase particles.Compared with Al-5wt.%Si-Al₂O₃ samples,the mechanical properties of Al-5wt.%Si-Al₂O₃-2.5wt.%Zr was improved significantly,the vickers hardness was improved from77.7HV to 85.5HV,tensile strength was improved from 211.2 MPa to 231.1 MPa,tensile yield strength was improved from 89.1 MPa to 114.6 MPa,the compressive strength was improved from 299.6 MPa to 343.1 MPa,compressive yield strength was improved from 174.2 MPa to189.8 MPa,the shear strength was improved from 151.6 MPa to 151.6 MPa,shear yield strength was improved from 87.6 MPa to 99.6 MPa.Compared with Al-5wt.%Si-Al₂O₃ samples,the mechanical properties of Al-5wt.%Si-Al₂O₃-xwt.%Y was decreased,and the Al-5wt.%Si-Al₂O₃-1.0%wt.%Y was the worst,and hardness was 68.0 HV,tensile strength was 129.0 MPa,tensile yield strength was 56.8 MPa,the compressive strength was 274.2 MPa,the compressive yield strength was 128.4MPa,the shear strength was 119.6 MPa,and the shear yield strength was 76.6 MPa.The fracture mechanism analysis shows that the fracture of pure aluminum silicon composites is a composite mechanism of brittle fracture and plastic fracture.The silicon particle was decreased with the addition of Zr,the mechanical properties of materials was improved obviously,and there also exist the second phase strengthening,the best performance and the most second phase exists in Al-5wt.%Si-Al₂O₃-2.5wt.%Zr.Y could refine the silica particles,but appear a large number of air hole in the process of hot isostatic pressing sintering,increase the number of the crack source,accelerate the propagation of crack and decreased the mechanical properties.