Ali Paşa Hekimoğlu

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.

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.

Effects of Contact Pressure and Sliding Speed on the Unlubricated Friction and Wear Properties of Zn-15Al-3Cu-1Si Alloy

ABSTRACT The unlubricated friction and wear properties of Zn-15Al-3Cu-1Si alloy were studied over a range of contact pressure (1–5 MPa) and sliding speed (0.5–2.5 ms−1) for a sliding distance of 2,500 m using a block-on-disc type test machine. It was observed that as the contact pressure increased, the friction coefficient of the alloy decreased but its working temperature, surface roughness, and wear volume increased. Sliding speed had no significant effect on the friction coefficient of the alloy but increased its working temperature, surface roughness, and wear volume. It was also observed that the formation of a hard and brittle surface layer had a great influence on the wear behavior of the experimental alloy. The hardness and thickness of this layer increased with increasing contact pressure and sliding speed. However, contact pressure was found to be much more effective on the hardness of the surface layer of this alloy. Both adhesion and abrasion were observed to be the dominant wear mechanisms for the alloy under the given sliding conditions. The results obtained from the friction and wear tests are discussed in terms of the test conditions and microstructural changes that take place during sliding.

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.

Relationships between mechanical and tribological properties of Zn-15Al-based ternary and quaternary alloys

Abstract Five ternary Zn-15Al-(1 – 5)Cu and six quaternary Zn-15Al-3Cu-(0.5 – 3)Si alloys were prepared by permanent mold casting for this work. Their unlubricated sliding friction and wear properties were investigated at a pressure of 3 MPa and a sliding speed of 1.5 m s−1 for a sliding distance of 2 500 m using a block-on-disc type tester. The friction coefficient and wear volume of the ternary alloys decreased with increasing copper content, but above 3 % Cu the trend reversed. As the hardness and both tensile and compressive strengths of the ternary alloys increased, their friction coefficient, working temperature and wear volume decreased. However, the trend reversed for the hardness and compressive strength of the quaternary alloys. The correlation between mechanical and tribological test results showed that the wear volume of Zn-15Al-based alloys can be determined in terms of their tensile strength.

Zn-15Al-3Cu-1Si alaşımı ve SAE 660 bronzunun yağlı durumdaki aşınma karakteristikleri

Bu calismada Zn–15Al–3Cu–1Si alasiminin yagli calisma kosullarindaki surtunme ve asinma davranislari blok-disk tipi bir deney duzenegi kullanilarak incelendi. Surtunme ve asinma deneyleri farkli yag debileri (0.25-3.0 cm 3 h -1 ), kayma hizlari (0.5 - 3.0 ms -1 ) ve basinclarda (1 - 8 MPa) gerceklestirildi ve sonuclar SAE 660 yatak bronzundan ayni kosullarda elde edilen sonuclarla karsilastirildi. Hem cinko esasli alasimin hem de bronzun surtunme katsayilarinin artan basinc ve yag debisi ile azaldigi, ancak kayma hiziyla onemli bir degisim sergilemedigi goruldu. Alasimlarin calisma sicakliklarinin artan yag debisi ile azalip artan basinc ve kayma hizi ile arttigi belirlendi. Alasimlarda asinma ile meydana gelen hacim kaybinin ise artan yag debisi ile azalip artan basincla arttigi, ancak kayma hizindan fazla etkilenmedigi goruldu. Ayrica, Zn–15Al–3Cu–1Si alasiminin belirtilen kosullarda SAE 660 alasimindan daha yuksek asinma direnci sergiledigi goruldu.