Mechanical properties and lubricated wear of Zn-25Al-based alloys

Abstract

Seven alloys based on Zn-25Al were produced as binary alloys or with silicon or copper ternary additions. Tensile properties, hardness and dimensional stability were studied in the as-cast state and as a function of aging. The lubricated wear behaviour was studied using a special pin-on-disc method and compared with that of SAE 660 bronze and SAE 73 brass. The addition of copper was found to be more effective than silicon in improving the mechanical properties of Zn-A1 alloys but silicon gave greatly improved wear resistance and dimensional stability. The wear resistance of Zn-Al-Si alloys was found to be superior to that of all the other materials tested. A heat treatment performed to simulate long term aging reduced the hardness and tensile strength of all the zinc-based alloys by about the same amount but improved ductility. The wear resistance was reduced by an increase in the break-in wear but was only significant for the alloy containing copper. It is concluded that Zn-Al-Si alloys have good bearing properties but may not have adequate strength after prolonged aging. An alloy with a composition close to that of ZA27, but with reduced copper and added silicon, may produce an improved combination of mechanical strength and wear resistance with a slight reduction in density.