The Research On Wear-friction Properties Of ZA40Alloy

In this thesis, ZA40alloy with3%Si element is the object of study. The impactof different heat treatment processes(T4and T6heat treatment) and the content ofmodifier(mixed sodium salt and rare earth) on microstructure, hardness and wearresistance of the alloy was investigated. The wear resistance of ZA40alloy wascompared with one of tin bronze and aluminum bronze. The microstructure,fracture mechanism and wear-friction characteristics of ZA40alloy wereresearched by OM, SEM, EDS, block-on disc friction testing experiment and othermethods. The main conclusions as shown below(1) The microstructure of as cast ZA40alloy consisted of aluminium-rich α dendritesphase, eutectoid α+η, ε phase and silicon particles. When the amount of RE addition is0.15%, the effect of modification comes to the best. RE modifier refines the α dendrites，inhibits the precipitation of eutectic silicon and prompts the precipitation of primary siliconin the way of block shape.(2) The addition of Ce-rich mixed RE can increase tensile strength andpercentage elongation, especially hardness. The fracture surface of tensile testspecimen shows a typical quasi-cleavage fracture. The tendency of ductile fractureincreases with RE content increasing. When the amount of RE addition is0.15%,the wear resistance of ZA40alloy come to the best.(3) The α dendritic structure of ZA40alloy was decomposed after being heatedto380℃solutionzed for4hours and quenched in water, The microstructure ofZA40alloy treated in the way was composed by supersaturated solid solution α′s(fcc)phase, and became homogeneous. Hardness of ZA40alloy solutionzed at380℃for4hours increased greatly.(4) The microstructure of solutionzed ZA40alloy transformed into steady αand η-Zn phases after100℃×2hour or200℃×1hour ageing treatment. Although thehardness decreased to some extent after ageing treatment, the wear resistance ofZA40alloy was improved(low friction coefficient and wear rate).(5) Under32#oil lubricated friction conditions, the stable friction coefficient of as cast alloy decreased with the load increasing first and then increased; thestable friction coefficient decreased with the load increasing for the380℃solutionzed for4hours alloy, and it almost didn’t change with applied loads forageing treated alloy. The wear resistance of ZA40alloy under the situation of lowspeed and heavy load was improved after solutionzing and ageing treatment.(6) Under dry lubrication friction conditions, the wear surface of as cast ZA40alloy is characterized by continuous deep grooves and scratches. Dry frictionmechanism was mainly abrasive wear, and included surface fatigue wear, oxidationwear and adhesive wear at the same time. While under lubricated frictionconditions, the wear surface consisted of some small wear debris, and lubricationfriction mechanism of as cast alloy was mainly abrasive wear. The wear surfaces ofheat treated samples were mainly formed by scratches, which were very smooth.The friction mechanism was mainly abrasive wear.(7) In mixed sodium salt and rare earth modified ZA40alloy, primary siliconparticles were refined and the shape was changed from sheet-block shape to nodularsilicon. The particles homogeneously distributed in the grain boundary. The resultsshow that the appropriate account of modifier addition is3%.(8) The wear resistance of heat treated and modified ZA40alloy is higher thanone of tin bronze and aluminum bronze.