Study on the mechanical and wear properties of Mg/sic/Gr hybrid metal matrix composite / Azzat Esam Abdulqader Al-Maamari

Faculty of Manufacturing and Mechatronic Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang – 2020

Includes bibliographical references

Nowadays, lightweight design with perfect mechanical properties is the major target in various industries, especially in the automotive and aerospace manufacturing. Therefore, magnesium (Mg) becomes one of the significantly demanding material for such industries in recent years due to its low density and high formability. However, Mg shows low wear resistance under insufficient lubricating conditions which limits its use in tribological applications. Therefore, self-lubricating materials are preferred because the solid lubricant contained in them can be automatically released during the wear process to reduce the wear. Graphite (Gr) is one of the materials which possess high lubricating characteristics. However, the limitation of graphite in adding magnesium matrix is that it significantly reduces the strength of the composite. Therefore, one solution could be to introduce a third material to the Mg-Gr composite to improve the strength of the composite. Silicon Carbide (SiC) is one of the popularly used ceramic materials whose introduction to the magnesium can increase the mechanical strength. The most important issue of composite fabrication is to maintain the uniformity of the reinforcement particles in the metallic matrix. The mechanical strength is significantly influenced by the particles homogeneity. Among the various fabrication techniques, powder metallurgy is considered to be an effective process as reinforcements uniformity can be achieved by this. Therefore, in this study, hybrid metal matrix composite (MMC) composed of magnesium matrix and SiC, Gr reinforcements has been developed by powder metallurgy technique and the effect of SiC and graphite content on the mechanical and the tribological behaviour of the Mg/SiC/Gr hybrid composite has been studied. The fabrication has been carried out in two phases. In the first phase, magnesium-graphite (Mg-Gr) composites with different weight percentage values of graphite were fabricated and their mechanical and wear properties were evaluated, and the optimum value of graphite was determined. After that, hybrid MMCs was fabricated by adding SiC and graphite reinforcement particles to the magnesium base material. At this stage, the percentage of the graphite particles kept constant (the value gave high wear resistance) but the percentage of SiC reinforcement varied in order to obtain the high mechanical properties. The raw powders with the desired percentage were mixed, compacted and sintered to produce the hybrid MMCs. The fabricated samples were then prepared for microstructural characterization, mechanical and tribological tests. The microstructure shows a proper bonding and uniform distribution of the reinforcement in the Mg matrix. The results revealed that all the mechanical properties, including hardness, tensile strength and flexural strength increases significantly and the tribological properties tremendously improved in the hybrid composite as compared to the pure magnesium and Mg-Gr composite. Moreover, the combined effect of 10% SiC and 5% Gr shows superior performance in both the mechanical and tribological properties.