Effect Of Pre-Compression And Thermo-mechanical Treatment On Wear Behavior Of ZK60 Magnesium Alloy

With low density,high specific strength and specific stiffness,excellent damping property,Magnesium alloy has a good potential application in the moving parts.When the magnesium alloy used as moving part,it may contact with other materials and there is relative movement,inevitably occur friction and wear.As one of the important plastic deformation mechanism of magnesium alloy at room temperature,Twins will have an important impact on friction and wear performance.Thus,twins are introduced into the ZK60 magnesium alloy by pre-compression along the extrusion direction.In this paper,the effect of twinning and thermo-mechanical treatment on the friction and wear mechanism and wear resistance of ZK60 magnesium alloy are studied.Main conclusions as below:(1)Pre-compress along the extrusion direction of ZK60 magnesium alloy bar.There are twins in the large grain after pre-compression.Twins parallel to each other in the same coarse grain.For ZK60 magnesium alloy after 7.3% pre-compression,whose average number of twin layers of the individual grains(LG)increases from 0 to 0.27 and the hardness increases from 69.8Hv to 82.2Hv,compare to the extruded magnesium alloy.Under 40 N wear load,when the pre-compression increases from 0% to 7.3%,the wear loss of ZK60 magnesium alloy significantly decreases from 18.4mg to 12.0mg.The wear width drops from 2.2mm to 1.7mm.The wear depth reduces from 75?m to 36?m.(2)Under 20 N wear load,the average friction coefficient of ZK60 magnesium alloy changes a little.The main wear mechanism of ZK60 magnesium alloy is abrasive wear and accompany with slight peeling wear.Under 40 N wear load,when the precompression increases from 3.6% to 7.3%,the average friction coefficient of ZK60 magnesium alloy apparently decreases from 0.211 to 0.119.Under 40 N wear load,ZK60 magnesium alloy occurs a serious peeling wear.But it forms a mechanical mixing layer on the surface of the 7.3% pre-compression sample,which effectively protect the surface of the sample,enhance the wear resistance of ZK60 magnesium alloy.(3)After the thermo-mechanical treatment,a large number of twins are introduced in the grains.The precipitated phase forms at the twin interface,which significantly improve the mechanical property of the alloy.Compared to the annealed specimen,the yield strength of the thermo-mechanical treatment specimen increases from 93 MPa to 243 MPa,and the compressive strength increases from 248 MPa to 384 MPa.When the wear load increases from 10 N to 40 N,the wear loss of the annealed sample increases sharply from 2.7mg to 17.7mg,the wear width increases from 1.4mm to 2.5mm,the wear depth increases from 20?m to 45?m;Under the 40 N wear load,the wear loss of the thermo-mechanical treatment specimen is only 6.2mg,the wear width is 2.0mm,and the wear depth is 30?m.So the thermo-mechanical treatment effectively enhances the wear resistance of ZK60 magnesium alloy.(4)When the wear load increases from 10 N to 40 N,the average friction coefficient of the annealed sample decreases sharply from 0.6979 to 0.2238;The average friction coefficient of the thermo-mechanical treatment specimen slowly decreases from 0.2091 to 0.1063.The wear mechanism of ZK60 magnesium alloy translates from mild wear(abrasive wear and oxidative wear)to severe wear(peeling wear and adhesive wear).