Studies on Aluminium Based Metal Matrix Composites Fabricated by Powder Metallurgy

Abstract

Composite materials are the material where two different materials are combined together to develop a new material which can be better compared to its individual constituent material. Metal matrix composite is an example of composite material where the base or primary material is reinforced with secondary materials such as metals, non-metals, and other materials such as ceramics and fibers. Metal matrix composites are fabricated for tailored properties, and they are superior to conventional materials in terms of specific properties. Metal matrix composites provide the scope of target properties, which can be according to particular applications like high strength to weight ratio, better creep resistance, controlled coefficient of thermal expansion, etc. This study deals with the fabrication of aluminium based metal matrix composite fabricated through the powder metallurgy route. Powder metallurgy is one of the popular processes of fabrication of metal matrix material owing to its relative simplicity as compared to other available processes. Mixing of powders is one of the important steps toward the successful fabrication of any material through powder metallurgy. This issue has been given due importance in the present research work for the fabrication of composites. An experimental study has been carried out to achieve an effective mixing of powders through a conventional V-blender and specially designed barrel mixer. These two mixing devices have been used for the mixing of powders of aluminium (matrix) and Silicon Carbide (reinforcement). The mixing performance of both the mixing device has been compared. The barrel mixer has been found to be better as compared to V-blender as the barrel mixer induces shear during the mixing of powders. The barrel mixer is provided with a helical agitator, which induces shear during the mixing of powders, and it improves the mixing effectiveness and reduces the overall mixing time to a great extent. Better dispersion of reinforcement particles has been achieved through barrel mixer in comparison to V-blender. During the fabrication of Al-MMC, Nanoparticles of reinforcement (nano SiC) have also been introduced along with micro-sized particles of reinforcement in the matrix of aluminium. The presence of nano particles affected the mechanical properties and density of Al-MMC. Microstructural studies revealed that nanoparticles owing to their size, could position iv themselves in the micro-porosity locations, and they could form compounds of SiC grains and impede the dislocation motion. As a result, the compressive strength of Al-MMC has been enhanced. Surface properties become of paramount importance when the part has such service application where relative motion is encountered. A hard and wear-resistant surface can sustain better in such conditions. To achieve this, laser treatment of Al-MMC at surface level has been attempted, and it is found that hardness and wear resistance both increased, making the Al-MMC a better wear-resistant material. Al-MMC has been extruded, and further, the effect of extrusion has been examined with regard to density and strength. Extrusion of Al-MMC resulted in the elimination of fine porosity and improved mechanical bonding, which is evident from improved density and increased strength. Machining of Al-MMC has been carried out to study the effect of SiC particles on tool wear. Al-MMC has been machined at various cutting speeds and feed rates. The tool wear and surface finish have been found affecting with the proportion of SiC content in Al-MMC and their fracture behavior. An overall study is accomplished, in which Al-MMCs have been fabricated through powder metallurgy, and it has been attempted to address the critical issues like the mixing of powders, role of nano reinforcement in enhancement of mechanical properties, the effect of laser processing on surface properties, and the effect of extrusion as a secondary process on the mechanical properties of Al-MMC.