Study On Wear Properties And Casting Techniques Of Zinc-based Alloy

Zinc-Aluminium based alloys have excellent mechanical and tribological properties,and can partially substitute tin bronze to prepare some wear-resistant and anti-friction components.Adding silicon into the zinc-aluminium based alloys can further improve their wear resistance.In this work,the dry sliding wear properties of ZA27-0.2Si alloy were investigated.Simultaneously,the wear properties wear compared with those of ZCuSn5Pb5Zn5 bronze under different loads and sliding speeds.The aim was to examine the substituting range for the bronze and provide some supports for practice.In addition,taking a machine tool bush as an example,the casting techniques of the ZA27-0.2Si were studied.The wear tests were performed on a pin-on-disk tester.The sliding speed ranged from 0.1 m/s to 0.7m/s and the loads ranged from lkg to 9kg,the testing time was 20min.The results indicated that the ZA27-0.2Si alloy had good wear resistance under low speed and high load which the ZCuSn5Pb5Zn5 alloy was suitable for applying under low speed and low load,which implied that the former alloy had a wider application range than the latter one.As the load increased,the wear mechanism of the zinc alloy changed in turn of adhesion and micro-machinging to abrasive wear accompanied by adhesion,plastic deformation induced wear and delamination wear.When the sliding speed increased,machining wear was enhanced and the smear wear finally occurred due to the temperature rise of the contacting surface.The microstructures of the wear surfuce and sub-surface layer determined the wear properties.The formation of transfer layer improved the wear properties.The wear mechanism of tin bronze was abrasive wear and sevre deformation occurred under high loads due to its low shear strength.The application of high temperature steel mould and cooling by water was benefical for directional solidification,so the bottom shrinkage could be overcome and inclusions and gas pores were easy floated.Suitable mould temperature and pouring temperature were the key factors for preparing casting without defects.In this work,the suitable casting parameters were the mould temperature 350℃of and pouring temperature of 580℃The application of high pouring temperature was necessary for preparing components without defects during sand mould casting.This could prolong the solidification time and was beneficial for floating of inclusions and avoid the formation of inclusions in the castings.The suitable sand mould casting technique was the application of bottom pouring.the ratio of sprue-runner-gate inner of 1:1.5:1.3,the pouring temperature 580℃...