Microstructure study of hot rolling nanosized in-situ Al2O3 particle reinforced A356 matrix composites

Abstract

In this study, A356 matrix and 0.2 vol.%∼0.8 vol.% in-situ Al2O3p/A356 composite were hot rolled to 75% reduction ratio and 0.6 vol.% composite was hot rolled to 75% and 83% reduction ratios. Scanning electron microscope (SEM), electron back scattering diffraction (EBSD) and transmission electron microscopy (TEM) were used to characterize the microstructure and texture evolution so as to investigate the effect of the particle content and reduction ratios. In the 75% rolling reduction, the Si phase in the A356 matrix and Al2O3p/A356 composites was fragmented and distributed along the rolling direction (RD), obvious Al2O3 agglomeration diminished. On the state of 75% reduction, when the content of Al2O3 was 0.2 vol.%, the composite had the finest grain size, however the 0.6 vol.% composite had a better Si phase and Al2O3 distribution. The Al2O3 particle in 0.2 vol.% sample can enhance the dislocation density and accelerate the sub-grain boundary formation. For the 75% reduction materials, the tensile properties increased with the increase of particulate content to 0.6 vol.% then decreased. The mechanical properties of 83% rolling reduction sample was better than the 75% reduction. Tensile tests showed that the ultimate tensile strength (UTS), yield strength (YS) and elongation (El) of 0.6 vol.% Al2O3p/A356 composite increased to 282 MPa, 221 MPa and 17.5%, respectively, due to the uniform distribution of the particles and refined Si phase upon increasing the rolling reduction to 83%, in combination with T4 heat treatment. In addition, the mechanisms of particle dispersion, recrystallization grain refinement and strengthening are also discussed.