Fabrication of A356-based rolled composites reinforced by Ni–P-coated bimodal ceramic particles

Abstract

Three arrangements of reinforced A356-based composites were fabricated. Samples with 3 wt% Al₂O₃ (average particle size: 170 µm), 3 wt% SiC (average particle size: 15 µm), and 3 wt% of mixed Al₂O₃–SiC powders (each reinforcement 1.5 wt%) were fabricated. The novel fabrication process of two-step stir casting followed by rolling was utilized. Analysis of the effect of using bimodal-sized ceramic particles and process parameters on the microstructure and mechanical properties of the composites was examined. Electroless deposition of nickel was used to improve the wettability of the ceramic reinforcements by the molten metal. From microstructural characterization, it was found that fine SiC particles were agglomerated, including when coated with Ni–P. It was also revealed that the rolling process broke the fine silicon platelets within the A356 matrix, which were mostly observed around the Al₂O₃ particles. The processed microstructure of the composite was altered in comparison to conventionally cast A356 MMC by translocation of the fractured silicon particles, by improving the distribution of fine SiC particles, and by elimination of porosities remaining after casting. A good bonding quality at matrix–ceramic interface was formed during casting and no significant improvement was found in this regard after the rolling process. The mechanical properties of the composites tested showed that the samples, which contained the bimodal ceramic particle distribution of coarse Al₂O₃ and fine SiC particles produced the highest levels of composite strength and hardness.