Effect Of Plastic Deformation On The Microstructure And Properties Of AIN Particles Reinforced Aluminum Matrix Composites

Aluminum matrix composites(AMCs)are being used widely in automotive industry,aerospace and other manufacturing industries owing to low density,high specific strength,excellent electrical and thermal conductivity and so on.In recent years,the shortcomings of limited strengthening effect by homogenous distributed reinforcements have been shown up and more and more researchers have tried to control the distribution of reinforcement at different scales,and then,a series of composites containing inhomogenous structures have been prepared.A large number of studies have shown that the introduction of reinforcement architecture can effectively improve the strength of composites at high temperature.However,the increase of strength is often accompanied by the decrease of ductility.Meanwhile,the matching of strength–ductility for a wide range of temperature usually has a large contradiction.In this study,Al N_p/Al composites were prepared through in situ liquid-solid reaction,and the microstructure and high-temperature mechanical behavior were regulated by rotary swaging.The mechanism of strength–ductility at room temperature was discussed by rolling treatment.The thermal stability of Al N_p/Al composites was also studied by thermal exposure.The main conclusions can be drawn as follows:(1)Effect of rotary swaging on microstructure and high-temperature mechanical properties of Al N_p/Al compositesThe rotary swaging was employed to tailor the spatial distribution of particles and the equivalent strains were 0.2,0.6.The results show the heterogenous lamellar structure consisting of particle rich zones and elongated?-Al grains of Al N_p/Al matrix composites have been manipulated and the particle distribution becomes much more uniform.The?-Al grains were also refined from 1.36?m to 0.77?m,0.72?m.The rapid softening of the composites at high temperatures can be retarded after RS treatment.The uniform elongation of the composites increased by 112%,from 0.99%to 2.1%,while the UTS at high temperature is comparable with the unprocessed one and only a slight decrease occurred from 126MPa to113MPa,achieving a good strength and ductility matching.A unique strain hardening retention was achieved,indicating a restored strain hardening after the regulation of the microstructure.Meanwhile,the strain rate sensitivity of the composites was also increased and m value of RS0.6 sample is nearly three times higher for than that of the EXT sample.The restored strain hardening,the higher strain rate sensitivity as well as the restrained strain localization at high temperatures account for the significant improvement of the composites'ductility at 350^oC.While,the pinning effects and load bearing efficiency of the Al N architecture decreased to some extent,leading to the slight loss of tensile strength.(2)Effect of rolling on microstructure and room-temperature mechanical properties of Al N_p/Al compositesThe rolling deformation was employed at room temperature and 300^oC with different reduction.The rolling at room temperature can improve the yield strength of composites,however,the UTS is almost unchanged and the elongation drops significantly.The results at300^oC showed that the yield stress of composites increased from 238MPa to 255MPa,286MPa,312MPa,the tensile strength increased from 312MPa to 314MPa,335MPa,360MPa.The Al N_p network structure was destroyed and more uniform microstructure had been achieved.Meanwhile,the microcracks were not found in the material.For the Al Np/Al composites with hierarchical structure,Al N_p network structure can effectively impede crack propagation,heterogeneous lamella structure can increase strain-hardening rate,and then the tensile strength improved along with the increase of uniform elongation.For the Al Np/Al composites after rolling,the hierarchical structure was destroyed and the increase of strength was mainly attributed to the accumulation of dislocations and the refinement of grain.The reduction of defects and the dispersion distribution of reinforcement contributed to the increase of elongation.(3)Effect of thermal exposure on microstructure and room-temperature mechanical properties of Al N_p/Al compositesThe thermal exposure was conducted at 350^oC and the hardness of composites increased from 80HV to 90HV in the first two hours.The thermal exposure was carried out at 500^oC.The tensile test at room temperature showed that the tensile strength?_b and yield strength?_0.2of composites increased first and then decreased with the increase of holding time.The peak of strength appeared at 10h,which was 374MPa and 316MPa,respectively.After 20h,the strength remains unchanged.After 500h,the tensile strength and yield strength remained at320MPa and 253MPa,which is slightly higher than the original one.At the same time,the trend of elongation was opposite to that of strength and the elongation remained at about 7%after 100h.The EBSD analysis showed that no obvious?-Al grain growth was found and the average grain size remained at about 1.42?m.The recrystallization fraction did not increase significantly,indicating that the Al N_p/Al composite exhibits excellent thermal stability.