The Influence Of Si、Sr And Cu Addition On The Microstrueture And Property Of Zn-75Al Alloy

ZA alloy,benefiting from its excellent mechanical properties,good resistance to reduce friction,advantages of raw materials and low manufacturing cost and other unique properties, has taken the place of traditional bearing materials,such as tin or lead base bearing alloy,Cu-Pb alloy bearing to make shaft, worm gear, slide and other wear-resistant parts,and obtained obvious economic benefit in actual production. Although zinc aluminum alloy has above-mentioned advantages,there are still some shortcomings,especially,sudden decline of mechanical property,sharp increase of friction coefficient,dimensional instability etc,in high temperature.In order to improve the defect of Zn Al alloy, based on increased Al content, this paper discusses the effect of Si, Sr and Cu on the structure property of Zn-75Al Alloy by using OM, SEM, MMU-10G abrasion testing machine and RPZ-2A the high temperature thermal expansion instrument.The conclusions are presented as follows.Addition of Silicon to Zn-75Al resulted in the formation of Eutectic silicon phase.It is evenly distributed when Silicon content in alloy is less than3%.Howeve,It becomes larger, exhibits a kind of micro-segregation, and precipitates a small amount of irregularly shaped primary silicon phase when Silicon content in alloy is more than3%.With the increase of silicon content, the Vickers hardness and the tensile strength of the alloys increases,while the elongation decreases.With the increase of silicon content, wear-resisting property of the alloys increases, the friction coefficient, wear volume and Subsurface microstructures of the alloys is minimum when silicon content is3%,the wear resistance of alloy is best. With the increase of silicon content, linear expansion coefficient of alloys decreases,dimensional stability improved obviously.The coarse needle, platy eutectic silicon become fine, homogeneous graininess, fibrous eutectic silicon, and a dendritic eutectic become rounded, close gradually, after the addition of Sr element in Zn-75Al-3Si alloy; After modification by Sr, the Vickers hardness and elongation of the alloys increases, while the tensile strength changes little; the wear resistance and dimensional stability of the alloys are better than Zn-75Al-3Si alloy. At200℃, coefficient of linear expansion changes from the original19.8141×10-6/℃to15.7537×10-6/℃,a decrease of25.8%, when Sr content is3%.θ(CuAl2) phase appears in Zn-75Al-3Si-0.04Sr alloy after the addition of Cu element, with the increase of Cu content, number and size of θ(CuAl2) phase increase, meanwhile, the Vickers hardness and the tensile strength of the alloys increase by24.8%comparing to Zn-75Al-3Si-0.04Sr alloy. The elongation of the alloy decreases gradually because the irregular shape of the θ phase splits matrix.Although the friction coefficient of the alloys increases with the addition of Cu element,wear volume and subsurface microstructures of the alloys decrease,especially under heavy load,the alloy exhibits excellent wear resistance.At the same temperature, linear expansion coefficient of alloys is smaller than ZA27alloy while the dimensional stability of alloys increases.