M.Sc. Tezi Görüntüleme | |||||||||||||||||||||
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| Summary: In this study, a series of ternary Al-7Si-Zn and quaternary Al-7Si-4Zn-Cu alloys were produced by permanent mould casting. The effects of zinc and copper additions on their microstructure, mechanical and tribological properties were investigated. It was seen that the microstructure of ternary Al-7Si-Zn alloys consisted of aluminium rich α-dendrites, eutectic and primary silicon particles. In addition to these phases, θ phase was observed in the microstructure of quaternary alloys containing copper. T6 and T7 heat treatments removed the dendritic structure of the alloy but had no considerable effect on the silicon particles. The density, hardness, yield, tensile and comprehensive strengths of ternary and quaternary alloys increased with increasing zinc and copper contents respectively, but their percent elongation and impact energy decreased as the zinc and copper contents increased. T6 and T7 heat treatment caused a significant increase in the yield and tensile strength of the Al-7Si-4Zn-3Cu alloy, but a small decrease in its percent elongation. Volume loss of ternary and quaternary alloys decreased with increasing zinc and copper contents up to %4 Zn and %3 Cu respectively; when the zinc and copper contents exceeded these levels it increased. The volume loss of alloys as-cast and heat-treatment states increased continuously with increasing applied load. As the sliding speed increased volume loss of the alloys in as-cast state decreased up to its certain level, above which it started to increase. However the reverse trend was observed to T6 and T7 heat treated Al-7Si-4Zn-3Cu alloy as compared to that in its as-cast state. It was observed that wear surface of the alloys were characterised by smeared layers, microcracks, fine scratches, oxidation and delamination.
Key Words: Al-Si Alloys, Mechanical Properties, Heat Treatment, Tribology. | |||||||||||||||||||||