Ph.D. Tezi Görüntüleme

Student:	Osman BİCAN
Supervisor:	Prof. Dr. Temel SAVAŞKAN
Department:	Makine Mühendisliği
Institution:	Graduate School of Natural and Applied Sciences
University:	Karadeniz Technical University, Turkey

Title of the Thesis:	Investigation of Microstructure and Mechanical and Tribological Properties of Al-25Zn Based Alloys Containing Copper and Silicon in the As-cast and Heat-treated Conditions
Level:	Ph.D.
Acceptance Date:	16/6/2010
Number of Pages:	133
Registration Number:	Di779

Summary:

In this study, one binary Al-25Zn, seven Al-25Zn-(1-5)Cu and six ternary Al-25Zn-3Cu-(1-5)Si alloys were prepared by permanent mould casting. Their friction and wear behaviour were investigated under different test conditions using a pin-on-disc machine. The results obtained from the tests were discussed in terms of structure and mechanical properties of the alloys and compared to those obtained from SAE 65 and SAE 660 conventional bearing bronzes.

The microstructure of the binary Al-25Zn alloy consisted of aluminum-rich α dendrites surrounded by eutectoid α + η phase. Addition of copper to this alloy produced intermetallic θ particles mainly in the interdendritic channels. The microstructure of the quaternary Al-25Zn-3Cu-(1-5)Si alloys revealed silicon particles, in addition to the phases observed in the ternary alloy. The stabilization treatment showed no significant effect on the microstructure of the Al-25Zn-3Cu-3Si alloy, but the T7 heat treatment removed its dendritic microstructure. The tensile and compressive strengths of the alloys increased with increasing copper and silicon contents up to 3%, above which the trend reversed. However, the hardness of the ternary and quaternary alloys increased continuously with increasing copper and silicon contents. The friction coefficient of the alloys decreased with increasing pressure, but the siding speed had no significant effect on it. However, the temperature and wear volume of the alloys increased with increasing pressure and sliding speed. Two different regions were observed underneath the wear surface of the Al-25Zn-3Cu and Al-25Zn-3Cu-3Si alloys. The formation of them was related to the microstructural changes resulted from heavy plastic deformation and recrystallization of the surface material and smearing of wear particles.

The Al-25 based ternary and quaternary alloys were found to be much superior to the SAE 65 and 660 bronzes as far as their mechanical and tribological properties are concerned. In addition, among the ternary and quaternary alloys the highest strength and wear resistance were obtained with Al-25Zn-3Cu and Al-25Zn-3Cu-3Si alloys, respectively.

Key Words: Al-25Zn Based Alloys, Microstructural and Mechanical Properties, Heat treatment, Test Parameters, Friction and Wear.