STRUCTURE AND PROPERTIES OF AL-BASED METAL MATRIX COMPOSITES

Abstract

In the present study, a non heat treatable aluminium alloy was reinforced with silicon and silicon carbide, respectively using an innovative disintegrated melt deposition technique (DMD). These two kinds of material produced as a part of present work are referred to as Al/Si and Al/SiC composites. The processing technique used involves disintegration of a composite slurry using gas jets followed by deposition of the resultant disintegrated slurry on a metallic substrate located at a pre-determined distance from the gas disintegration point. In order to minimise porosity and obtain an improved mechanical properties, both DMD processed Al/Si and Al/SiC composites were subsequently extruded. Chemical composition analysis following processing was carried out to determine the extent of silicon and silicon carbide incorporation in the aluminium alloy. The results revealed that more silicon in comparison to silicon carbide was incorporated irrespective of starting with the same weight percentages of each element. The microstructural and mechanical properties characterisation were conducted on both the as-processed and extruded Al/Si and Al/SiC composites. The results of microstructural characterisation on the as-processed materials revealed the presence of finite amount of porosity and acceptable distribution of Si and SiC particles. The results of the microstructural characterisation following extrusion revealed, in common, minimal presence of porosity, uniform distribution of Si and SiC in the matrix, improved and nearly identical Si-Al and SiC-Al interfacial characteristics and reduced grain size for both the Al/Si and Al/SiC materials when compared to that in as-processed condition. The solutionizing and ageing studies were carried out on the as-processed and extruded Al/Si samples to establish the peak hardness condition. The results of hardness measurements revealed that the maximum hardness can be obtained only for a certain ageing time. The results of the tensile testing revealed significant improvement in tensile properties for both Al/Si and AI/SiC after extrusion. Furthermore, results also revealed relatively superior combination of tensile strength, ductility and matrix microhardness in the case of aluminium alloy containing silicon when compared to the aluminium alloy reinforced with silicon carbide. The results of mechanical properties characterisation were finally correlated with constitutional and microstructural aspects of metallic matrix.