Systematic Investigation Of Friction And Wear Performance Of GW103Magnesium Alloys

In this study, both friction and wear performance in dry sliding andlubricated sliding of Mg-10Gd-3Y (GW103) series magnesium alloys areinvestigated using a ball-on-flat reciprocating wear configuration underdifferent loads, sliding speeds and temperature. Using optical microscopy(OM), scanning electron microscopy (SEM), Vickers hardness testing andtensile testing and other characterization techniques, the wear mechanismsand the influence of microstructure, mechanical properties, and grain size onfriction and wear properties are investigated systematically.Dry sliding wear behavior of hot extruded GW103K magnesium alloyagainst AISI52100bearing steel has been investigated. Wear rates andfriction coefficients were measured in a load range of3~15N, sliding speedrange of0.02~0.2m/s, and temperature range of298~473K at a constantsliding distance of500m. Microstructures of worn surfaces and wear debriswere characterized to identify the wear mechanism. Results show that withincreasing applied load, the wear rate increases, and the wear mechanismstransform from abrasion to oxidation, and to delamination. The wear ratedecreases with increase in sliding speed. While delamination is dominated atvery low sliding speed (0.02m/s), oxidation is dominated at sliding speedabove0.14m/s, where frictional heating leads to surface temperature raisingabout110-130K. The wear rate increases with sliding temperature throughsevere delamination mechanism. However, at473K, a mixed mechanicallayer of deformable wear debris is formed through frictional heating resultingin wear rate reduction. The friction coefficient decreases with load andsliding velocity. The relationship between friction coefficient and load is discussed from thermodynamic aspects.By comparison of hot-extruded, T5, as-cast and T6GW103K magnesiumalloy, as-cast GW103magnesium alloy and AC8A aluminum, it can be foundthat under the same conditions, both the friction coefficient and wear rates ofGW103series magnesium alloy are lower than AC8A aluminum alloy. Thevariation of friction and wear of GW103alloy is similar, but the wear rate ofAC8A aluminum alloy increases with speed, unlike magnesium alloys. As thetemperature rises to473K, AC8A adheres to the steel ball, indicating thathigh-temperature wear resistance is worse than that of GW103alloys. Heattreatment improves the wear resistance, which may result from the reductionof second phase and increment of the cuboid-shaped and thermally stablephase. The wear resistance of GW103K cast magnesium alloy containing Zris worse than Zr-free GW103cast alloy, indicating that the grain size mayhave effect on the wear resistance.Under the oil lubrication, the friction coefficient is much lower thanunder the dry friction due to the oil film between the counterface, and thevalue between0.06and0.09indicates that the wear process is under theboundary lubrication state. Moreover, the wear rate in oil-lubricated state isonly about5%of that in dry sliding. The friction coefficient decreases withload or speed, however, the wear rate increases with load or decrease ofspeed. Although the results are similar to dry sliding, the wear mechanismunder oil lubrication condition is abrasion wear, and no oxidation ordelamination wear occurred, possibly due to negligible temperature rise.Under the oil lubrication, as the load increases, the oil film becomes thin,causing an increment in asperity contact, and resulting in the increment ofwear rate; as the speed increases, the film layer becomes thick, and both thefriction coefficient and wear rates are reduced.