Researches On Wear Behaviors And Mechanisms Of Deformed Magnesium Alloy Fabricated By Extrusion-Shear

Extrusion-Shear(ES)process for magnesium alloy is a newly developed plastic deformation technique which combines Direct Extrusion with ECAP. Grains of ES-processed magnesium alloys can be effectively refined and mechanical properties can be improved, but the tribological properties have not been studied. Based on studies of microstructures and mechanical properties of magnesium alloys and finite element simulation of wear, friction and wear behaviors of deformed magnesium alloy have been studied in this paper.To study microstructures and mechanical properties of deformed magnesium alloys, XRD, Metallographic Experiment and Microhardness test have been conducted on deformed magnesium alloys which were processed by different ways of plastic deformation(Extrusion-Shear and Direct Extrusion), under different deformation temperatures, using molds with different channel angles and billets in different original states, respectively. Results indicate that the microstructure of ES deformed magnesium alloy have been more effectively refined due to the shearing of channel angles in ES process, compared with Direct Extrusion. Grains of ES-processed AZ31 magnesium alloy extruded under 370℃ are fine, but grains slightly grow up and the microstructures are inhomogeneous when extruded under 400℃and 420℃. Microstructure of ES-processed AZ61 magnesium alloy is finer and more homogeneous when extruded using mold with channel angle of 120° than using mold with channel angle of 135°. Microhardness values of AZ-series magnesium alloys prepared under different plastic deformation parameters display quite small differences, reaching around 60 HV.Reciprocating sliding fiction and wear behaviors of AZ31 magnesium alloys prepared by different plastic deformation manners(Extrusion-Shear and Direct Extrusion) and under different deformation temperatures have been studied and compared, respectively. Besides, fiction and wear behaviors of AZ61 magnesium alloy extruded using molds with different channel angles and billets in different original states have also been studied. Influences of Extrusion-Shear process parameters on wear properties of deformed magnesium alloys have been analyzed according to fiction coefficients and wear rates. Meanwhile, combining SEM and EDS analyses of worn surfaces and wear debris, wear mechanisms in different fiction conditions have been discussed. It turned out that the wear resistance of ES-processed magnesium alloy was better than that of the alloy prepared by Direct Extrusion. AZ-series magnesium alloys prepared by ES process under deformation temperature of 370℃ and using a mold with channel angle of 120° showed better wear resistance. ES deformation magnesium alloys prepared with homogenization treated billets and untreated billets showed a similar wear resistance. Wear mechanism changed from mild wear(adhesion, abrasion and oxidation) to severe wear(delamination, plastic deformation and melting) with the increase of normal load and reciprocating frequency. Wear processes of ES-processed and Direct Extruded AZ31 magnesium alloy and ES deformed AZ31 magnesium alloy under different reciprocating frequencies have been simulated using finite element software DEFORM-3D. The stress distributions in contact regions at the initial loading stage have also been simulated. Distributions and changes of stress and strain indicated that under same friction conditions, the degree of plastic deformation in ES deformed magnesium alloy was smaller than in direct extruded alloy, that is to say the wear resistance was relatively good. The effective stress and strain were found increasing with the increase of applied load, but decreasing with the increase of reciprocating frequency. The results suggested that plastic deformation and delamination were caused by cumulative stress and strain and increased wear degree of the metal surface.