Spray processing of 2014-Al + SiCP composites and their property evaluation

Abstract

Aluminium alloy (2014-Al alloy)-based metal matrix composites containing SiCP particulates were produced by spray co-deposition. The mass median diameter and mass flow rate of SiCP were varied from 6 to 30 μm and from 10 to 30 mass% of the melt flow rate respectively. Spray formed billets of 200 mm diameter and 400 mm height were produced. Porosity and SiC content were measured at different positions in the preform. The mass fraction of reinforcement incorporated in the preform varies from 6 to 15%. Porosity is observed to increase with the increase in the surface area of the reinforcement/matrix interface. Optical microscopy shows a uniform distribution of particulates. Smaller size particles are pushed towards the grain boundaries during solidification of the deposit, in contrast to their large size counterparts. The matrix grain size varies from 15 to 50 μm with the variation in size and content of reinforcement particles. The grain size of the matrix decreases with the increase in the SiCP content. This decrease in the grain size is more sensitive to the size of the reinforced particulates, i.e. smaller size particulates give rise to a better refinement. Microstructural examination of overspray powder particles shows that the collision of melt droplets and SiC particles is the major mechanism for the incorporation of small particles. The ageing behavior of composites was studied at different temperatures for various sizes and volume fractions of particles, and the mechanical properties were evaluated. Composites with smaller particulate size show an early hardness peak than those with larger size particulates. Composites reinforced with intermediate size of SiCP particulates show an increased elastic modulus compared to unreinforced alloy.