Temel Savaşkan

Wear resistance and microstructure of Zn-Al-Si and Zn-Al-Cu alloys

Abstract Two Zn-Al-based ternary alloys containing 2 and 5 wt.% Si and one containing 5 wt.% Cu were produced by casting. Their dimensional stability and microstructures were investigated in the as-cast and heat-treated conditions. In a lubricated sliding wear test, a comparison was made of the wear behaviour of these alloys with that of SAE 660 phosphor bronze. It was shown that the Zn-Al-Si alloys were the best materials of those tested in terms of dimensional stability and higher wear resistance under intermediate speed and high load conditions.

Dry sliding friction and wear properties of zinc-based alloys

Abstract The friction and wear of two near-eutectoid and two monotectoid permanent-moulded zinc-based alloys and an SAE 660 bronze for comparison were investigated under dry sliding conditions. To determine the wear mechanisms surface and subsurface microstructures of worn test samples were examined by scanning electron microscopy (SEM). All of the zinc-based alloys had lower coefficients of friction and higher wear resistance than the bronze; the best wear resistance and lowest coefficient of friction were obtained for the ZnAl40Cu2Si1 alloy. Wear resistance increased strongly with hardness and tensile strength and decreased with friction coefficient. Correlation of the experimental results showed that the wear behaviour of the zinc-based alloys was consistent with Archhard’s equation. Layered structures were formed under the wear surfaces of the zinc-based alloy samples during testing. The topmost layer, formed by smearing and embedding of oxidised zinc–aluminium alloy was hard and is considered to have contributed to their low wear rates. Surface and subsurface examinations showed that adhesion and smearing was the main wear mechanism for the zinc-based alloys, while abrasive wear dominated in the case of the SAE 660 bronze.

Effect of copper content on the mechanical and sliding wear properties of monotectoid-based zinc-aluminium-copper alloys

Abstract One binary zinc-aluminium monotectoid and five ternary zinc-aluminium-copper alloys were produced by permanent mould casting. Their wear properties were examined using a block-on-ring test machine. Hardness, tensile strength and percentage elongation of the alloys were also determined and microhardness of aluminium-rich α phase was measured. It was observed that the hardness of the alloys increased continuously with increasing copper content up to 5%. Their tensile strength also increased with increasing copper content up to 2%, but above this level the strength decreased as the copper content increased further. Microhardness of the aluminium-rich α phase was also affected by the copper content in a manner similar to that of the tensile strength. It was found that the wear loss of the alloys decreased with increasing copper content and reached a minimum at 2% Cu for a sliding distance of 700 km. However, the coefficient of friction and temperature due to frictional heating were found to be generally less for the copper containing alloys than the one without the element. The effect of copper on the wear behaviour of the alloys was explained in terms of their microstructure, hardness, tensile strength, percentage elongation and microhardness of the α phase.

Sliding wear of cast zinc-based alloy bearings under static and dynamic loading conditions

Abstract The lubricated wear behaviour of cast journal bearings, produced from a series of zinc-based alloys and SAE 660 bronze as a reference material, was investigated under both static and dynamic loading conditions using a bearing test rig. All of the zinc-based alloys had higher wear resistance than the SAE 660 bronze. Among the zinc-based alloys, the wear resistance of the monotectoid-based alloys was superior to those based on near-eutectoid composition, and the best wear performance under both static and dynamic loading conditions was obtained with ZnAl40Cu2Si1 alloy. Copper content affected the wear resistance of monotectoid zinc-based alloys. Under dynamic loading conditions, it increased with increasing copper content up to 2%, but declined thereafter. Tensile properties and hardness of the monotectoid alloys were also affected by their copper content. Loading conditions had a strong influence on the wear rate. Under static loading conditions, as-cast zinc-based alloys showed higher wear resistance than the equivalent heat-treated alloys, but this behaviour was reversed for dynamic loading. Possible reasons for this are briefly discussed.

Effect of Copper Content on the Mechanical and Tribological Properties of ZnAl27-Based Alloys

One binary ZnAl27- and five ZnAl27-based ternary alloys containing 1–5% Cu were produced by permanent mould casting. Their friction and wear properties were examined using a block-on-ring test machine after determining their hardness and tensile strength. It was observed that the hardness and tensile strength of the ZnAl27-based ternary alloys increased with increasing copper content up to 2% due to solid-solution hardening, above which their tensile strength decreased, while hardness continued to increase. This is attributed to the formation of copper-rich ε and T′ phases, which reduce the solid-solution hardening of the alloys. It was found that the wear volume loss of the ZnAl27-based alloys decreased with increasing copper content up to 2% but showed a small increase above this level. Therefore, it was concluded that the wear resistance of ZnAl27-based alloys containing 1 to 5% Cu correlates well with their tensile strength. In addition, smearing and scratches were found to be the main features of the wear surfaces of the ZnAl27-based alloys under static loading and lubricated sliding conditions.

Relationships between secondary dendrite arm spacing and mechanical properties of Zn-40Al-Cu alloys

Three ternary monotectoid-based Zn-40Al-(1, 2, 3%) Cu alloys were produced by permanent mould casting at different pouring and mould temperatures. The average cooling rate for each alloy was determined. Structure of the alloys was examined using optical and electron microscopes and their hardness, tensile strength, percentage elongation and impact energy were measured. As a result of these investigations the relationships between structure and mechanical properties of the alloys were determined.It was observed that the secondary dendrite arm spacing of the alloys decreased with increasing cooling rate and their hardness, tensile strength, percentage elongation and impact energy increased. Correlation of experimental results showed that the hardness, tensile strength, percentage elongation and impact energy of the alloys could be related to their secondary dendrite arm spacing using straight line equations.

Fatigue properties of zinc-aluminium alloys in 3.5% NaCl and 1% HCl solutions

Abstract A series of binary zinc–aluminium alloys were produced by permanent mould casting. Fatigue behaviour of the alloys was investigated in 3.5% NaCl and 1% HCl solutions using a rotating bending fatigue machine. The stress amplitude versus number of cycles to failure curves of the alloys were obtained for both environments. The fatigue strength and fatigue lifetime of the alloys were found to be very sensitive to these environments. Acid solution was found to be much more effective on the fatigue behaviour of these alloys than the salt water. It was also observed that the fatigue lifetime of the alloys decreased with increasing aluminium content and as the aluminium content increased their sensitivity to corrosive environments increased. It was also found that Basquin’s law could be used to express the fatigue behaviour of the zinc–aluminium alloys in these environments.

Friction and Wear Properties of Zn-25Al-Based Bearing Alloys

A series of Zn-25Al-based ternary and quaternary alloys was prepared by permanent mold casting and their dry sliding friction and wear properties were investigated using a block-on-disc machine. The hardness and strength of the alloys increased with increasing copper and silicon contents, but when the copper and silicon contents exceeded certain levels the trend reversed. However, their impact energy and ductility showed completely opposite changes with copper and silicon contents. T6 heat treatment increased the hardness and strength of Zn-25Al-3Cu-1Si alloy but reduced its impact energy, ductility, and wear resistance. The working temperature and wear volume of the alloys increased almost linearly with increasing sliding distance and contact pressure, but the latter had no considerable effect on their friction coefficient. Microstructural changes that resulted in the formation of different regions were observed below the wear surface of the alloys. The formation of these regions was discussed in terms of deformation of surface material, oxidation, and smearing of wear particles. The Zn-25Al-based ternary and quaternary alloys were found to be much stronger and more wear resistant than SAE 660 bronze.

Effect of quench–ageing treatment on the microstructure and properties of Zn-15Al-3Cu alloy

Abstract In order to determine the effect of quench–ageing treatment on the microstructure and properties of Zn-15Al-3Cu alloy, it was prepared by permanent mould casting and then solution treated at a temperature of 330 °C, quenched and aged at 180 °C. The changes in the microstructure, length, hardness, strength and ductility of the quenched alloy were monitored during ageing. The microstructure of the alloy in the as-cast condition consisted of β dendrites and α, η and ∊ phases. However, solution treatment followed by quenching removed the lamellar microstructure of the alloy and produced a supersaturated β solid solution. Subsequent ageing resulted in transformation of β solid solution to α and η phases and conversion of metastable ∊ phase to stable T′ compound. Appropriate ageing times for T6 and T7 heat treatments of this alloy have been determined according to the experimental results.

Structure and mechanical properties of Zn-(5–25) Al alloys

Abstract In order to determine the most suitable chemical composition for the basis of zinc-based ternary and quaternary alloys, five binary Zn-(5–25) Al alloys were prepared by permanent mould casting. Their microstructures and mechanical properties were investigated using metallography and hardness, tensile and compression tests. The microstructure of Zn-5Al alloy consisted of eutectoid α + η and eutectic η phases. However, the microstructures of relatively high aluminium-containing alloys (Zn-10Al and Zn-15Al) consisted of proeutectic β dendrites surrounded by η phase and small rounded α particles. The near eutectoid alloys (Zn-20Al and Zn-25Al) exhibited similar microstructures to those of Zn-10Al and Zn-15Al alloys, but with α-cored β dendrites surrounded by α + η particles. As the aluminium content increased the hardness and strength of the alloys increased, but their impact energy and density decreased. The total percentage elongation of the alloys also decreased with aluminium content, but after showing an initial increase. These observations are discussed in terms of the microstructural features of the alloys.