Microstructure And Properties Of As-extruded Al₂O₃/7075 Composites

In this paper,the as-cast Al₂O₃/7075 blank was prepared by high-energy ultrasonic technology.Then the as-extruded Al₂O₃/7075 composite with high strength and good elongation was successfully prepared by hot extrusion process.The effect of Al₂O₃ content and high-energy ultrasonic parameters on the mechanical properties and microstructure of as-cast Al₂O₃/7075 blank were studied.After obtaining the as-cast composite blank with good performance,the blank was processed by hot extrusion.The effects of extrusion temperature and extrusion ratio on the microstructure and mechanical properties of the as-extruded composite were studied.The wear behavior of as-cast and as-extruded composites were also analyzed.The wear mechanism and wear surface of different composites were analyzed and explained.The results show that Al₂O₃ can be uniformly dispersed in the composite by high-energy ultrasonic waves when the content of Al₂O₃ is less than 2.0wt%.Beside that,the ultimate tensile strength and microhardness of the Al₂O₃/7075 composite can be increased with the increase of Al₂O₃ content.When the Al₂O₃ content was 2wt.%,the ultimate tensile strength and hardness of the composite reached the maximum values,which were 270.30 MPa and 115.2 HV,respectively,and increased by 33.08%,and 28.6%,respectively,relative to the 7075 matrix.Although the ultimate tensile strength and hardness of the composite increased with the addition of Al₂O₃,the plasticity of the composite does not increase much,the elongation of the composite is about 1-2%.After the composite was processed by a hot extrusion process with an extrusion ratio of 20:1 and an extrusion temperature of 460°C,the ultimate tensile strength,hardness and elongation of the composite reached the maximum values,which were360.26 MPa,170.34 HV and 11.00%respectively,and increased by 77.38%%,74.53%and 848%,respectively,relative to the 7075 matrix.When the extrusion temperature is lower than 440°C,the Al₂O₃ clusters can be observed in matrix,and the dispersion of the Al₂O₃ particles is more uniform until the extrusion temperature reach 460°C.However,when the extrusion temperature was continuously increased to 480°C,the dispersion of the Al₂O₃ particles did not change much,but the tensile properties were lowered because of the generation of the Mg₂Si phase.After comparing and analyzing the wear behavior of composites under different processes,the results show that the wear rate of as-excluded composite is reduced by an order of magnitude compared with the as-cast composites under the same wear environment.The wear resistance of as-extruded composite is much better than that of as-cast composite.