Sliding wear map for the magnesium alloy Mg-9Al-0.9 Zn (AZ91)

Dry sliding wear tests were performed on a Mg-9.0%, Al-0.9%, Zn (AZ91) allo y using a block on-ring (AISI 52100 steel) configuration. Wear rates were m easured within a load range of 1-350N and a sliding velocity range of 0.1-2 .0 m/s Compositions, morphologies and microstructures of worn surfaces and wear debris were characterised by scanning electron microscope (SEM), energ y dispersive X-ray spectrometer (EDS) and X-ray diffractometer (XRD). A wea r mapping approach, consisting of identification of micromechanisms of wear leading to the generation of loose debris and surface damage and determina tion of the range of applicability of each mechanism as a function of load and speed, has been adopted. Two main wear regimes, namely a mild wear regi me and a severe wear regime have been observed. The role of contact surface temperature on the mild to severe wear transition was investigated in deta il. It was shown that the transition from mild to severe wear was controlle d by the contact surface temperature of the alloy and that the onset of the severe wear coincided with a surface temperature of 347 K. in the mild wea r regime two different micromechanisms operated, i.e. two sub-wear regimes, namely an oxidational wear regime and a delamination wear regime, were ide ntified. Similarly, in the severe wear regime two different wear mechanisms were responsible for surface damage and debris formation. These were class ified as the severe plastic deformation induced wear and the melt wear regi mes. The results of wear tests and metallographic investigations on worn su rfaces have been summarised in a wear mechanism map. An empirical contact s urface temperature model, which serves to predict the critical surface temp erature at the onset of severe wear, has been developed. (C) 2000 Published by Elsevier Science S.A.