Research On Microstructure And Properties Of Extruded Profile Of TiB₂ Particulate Reinforced 7075Al Composite

With the rapid development of aerospace,national defense,transportation and other fields,traditional aluminum alloys are no longer able to meet the extremely high requirements for mechanical properties and corrosion resistance under strict service conditions.Compared with aluminum alloy,particle reinforced aluminum matrix composites have higher specific strength,higher wear resistance,lower coefficient of thermal expansion and better high-temperature resistance,which is an important development direction of light metal structural materials.In recent years,TiB2/7075A1 composites using TiB2 particles and 7075 aluminum alloy as strengthening phase and matrix have received widespread attention from researchers due to their excellent performance.The previous research on TiB2/7075Al composites mainly focused on the preparation methods,but there were few reports on their corrosion behavior,solution and aging heat treatment,and high-temperature performance.In this study,the TiB2/7075Al composites were prepared by powder metallurgy method,followed by hot extrusion and solution aging heat treatment experiments.The focus is on studying the changes in microstructure,corrosion resistance,and room temperature/high temperature mechanical properties of the composites,and clarifying the main factors affecting the corrosion resistance and mechanical properties of the composites.This study provides theoretical guidance for the preparation,extrusion forming,and heat treatment process of TiB2/7075Al composites,and has important theoretical significance and engineering application value.The main conclusions of this study are as follows:(1)TiB2/7075Al composites plate-shaped profiles with TiB2 particle content of 0 wt.%,2 wt.%,6 wt.%,and 10 wt.%were prepared based on powder metallurgy and extrusion forming.The effects of TiB2 particle content on intergranular corrosion,exfoliation corrosion,stress corrosion,electrochemical corrosion,and frictional wear of TiB2/7075Al composites were studied.It was found that TiB2 particles inhibited the corrosion channel and crack propagation of TiB2/7075Al composites,improved the resistance to intergranular corrosion and peel corrosion of TiB2/7075Al composites,and reduced the sensitivity of the composite to stress corrosion.TiB2 particles damage the integrity of the oxide film on the anode surface,resulting in lower electrochemical corrosion performance of TiB2/7075Al composites than 7075A1 alloy.TiB2 particles promote the occurrence of dynamic recrystallization during the extrusion process,thereby refining the grain structure of TiB2/7075Al composites.With the increase of TiB2 particle content,the friction coefficient and texture strength of TiB2/7075Al composite decrease,and the wear resistance improves.(2)The 7075Al alloy plate-shaped profiles and TiB2/7075Al composites plate-shaped profiles were subjected to solution and aging heat treatment,and the changes of microstructure and mechanical properties during extrusion,solution and aging were studied.It was found that the interfacial reaction between TiB2 particles and 7075Al matrix occurred during high temperature solution,resulting in the enrichment of Mg elements at the interface,forming a continuous Mg-containing layer.The addition of TiB2 particles did not change the precipitation sequence of 7075Al matrix,but caused the lack of Mg element in 7075Al matrix,which significantly delayed the precipitation kinetics of 7075A1 matrix.The TiB2/7075Al composites exhibit higher strength,better wear resistance and lower friction coefficient than 7075Al alloys in all conditions.(3)The 7075Al alloy plate-shaped profiles and TiB2/7075Al composites plate-shaped profiles were subjected to solution and aging heat treatment to achieve peak aging(T6)state,and the comparative studies were conducted on their microstructure and mechanical properties under high temperature environments.It was found that the friction coefficient of TiB2/7075Al composites increases with the increase of friction and wear temperature.The TiB2 particles can reduce the high temperature friction coefficient of the composites,and improve the high temperature wear resistance and tensile properties.With the increase of tensile temperature,η’phase changes to η phase in TiB2/7075Al composites and 7075Al alloy,and the η phase size increases.At 300℃,the η’ phase gradually decomposed into Mg and Zn atoms,and the η phase absorbed Mg and Zn atoms and kept growing.Under the condition of high temperature tensile,the size of precipitated phase in TiB2/7075Al composites is smaller than that of 7075Al alloy,resulting in higher high temperature strength of TiB2/7075Al composites than that of 7075Al alloy.The strength decline of TiB2/7075Al composites and 7075Al alloy under high temperature tensile condition is caused by the softening of aluminum matrix and the second phase transition.