High strength and high ductility nano-Ni-Al2O3/A356 composites fabricated with nickel-plating and equal channel angle semi-solid extrusion (ECASE)

The nano-Ni-Al2O3/A356 nanocomposites prepared with nickel-plating, stir casting, and equal channel angle semi-solid extrusion (ECASE). The microstructure, tensile property, and fracture morphology of the fabricated nanocomposites have been investigated. The microstructure observation showed the nickel-plating could stimulate nucleation and break nanoparticle aggregation, resulting the matrix grains in a smaller size (63 mu m) and the nanoparticles more uniform located on the grain boundary. The ECASE could further refine the grains size (23 mu m) and improve the nanoparticle dispersion. Although 5 passes refine the grains to 16 mu m, it would cause the particles to re-agglomerate, due to the nanoparticles exist in the semi-solid liquid phase for a long time. The fabricated nanocomposites exhibited an enhancement in both strength and ductility, about 1.2-2.5 times higher than those of the corresponding aluminum matrix composites. Due to the Orowan strengthening and fine grain strengthening, i.e., increased the number of grain boundaries and improved the resistance of particles to cooperative grain deformation. Meanwhile, the ECASE eliminated the intergranular defects and improved the grain boundary bonding. The enhanced mechanical properties of the nanocomposites were attributed to the grain boundary control increased by the nickel-plating and ECASE. The grain boundary control, such as increasing the grain boundary number, improving the particle-matrix adhesion and particle dispersion, can be applied to the development of high mechanical properties aluminum matrix composites. (C) 2021 The Authors. Published by Elsevier B.V.