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Production and characterization of aluminum matrix composites for small-scale unmanned aircraft engine pistons

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2020
Demiralp, Muammer
The composite materials are used in every stage in life, from the aerospace industry to agriculture. In most composites, the primary purpose of adding reinforcement to the matrix material is to increase the strength and stiffness of the matrix. Nowadays, most engineering materials are replaced with the composite materials due to higher specific strength. In this study, particle reinforced metal matrix composite is used to produce pistons for a small-scale unmanned aircraft engine. Conventional pistons are produced from the Al-Si alloy which has high-temperature resistance with the addition of 1 wt.% each of Cu, Mg, and Ni. These elements are added to increase the strength of the alloy. High Si content provides a lower expansion coefficient and higher wear resistance; however, it decreases the strength of the piston. The heat treatment of piston alloy is generally T5 and T6. They consist of three steps; solution treatment, quenching, and ageing. Solution treatment aims to dissolve soluble phases Cu and Mg formed during solidification, to mix the alloying elements and to modify Si particles. The higher solution treatment temperature means higher strength after heat treatment and a higher rate of these three processes. Pistons are generally deformed from the head part due to the high-temperature cycle load. Therefore, the head of a piston should be modified to increase the piston life.This modification can be modal or compositional. That is to say, to increase the piston life, either the design of the piston should be changed, or the material of piston should be improved. Therefore, in this study, the material of the piston head was replaced with the metal matrix composite material. The matrix of this composite is near eutectic Al-Si powder with the addition of 10 wt. % of silicon carbide particles (F320 type) as reinforced materials. Production was taken place by using squeeze casting techniques. The characterizations of the new pistons and conventional ones were done. The results were collected and compared to their performances, physical, and chemical properties. Then, the results show that the composite pistons, especially produced by the Rheo-sintering technique, have superior mechanical properties such as higher wear resistance, higher fatigue life, and higher flexural strength.