Friction and wear maps of Mg-Er alloys with varying Er content

Abstract

Several rare-earth (e.g. Y, Gd, Nd, Ce) additions have been investigated till date in magnesium alloys. However, limited efforts have been made to examine the influence of Erbium (Er) in Mg alloys. This study is designed to unravel the role of Er addition on wear and friction characteristics of Mg-Er alloys. As-cast Mg-Er (0.5–12 wt%) alloys were prepared and tested under dry sliding conditions with varying normal loads (5 N to 100 N) and sliding speeds (0.01 m/s to 0.1 m/s). The results indicated that the addition of Er to Mg significantly improved the overall wear properties of the alloys. At higher Er content, a substantial decrease in severe wear rate region (75 %), while a ⁓ 40 % reduction in friction coefficient were observed. The formation of a protective tribo-oxide layer at the contact zone due to the increase in temperature from friction, combined with the strengthening effect of the Er-rich precipitates, contributed to enhanced wear resistance with Er addition. The surface energy of the Mg-12Er alloy was less than that of other Mg-Er alloys (⁓ 50 % reduction), causing reduced adhesion and abrasion wear and thus reducing the overall wear rate. Furthermore, it was observed that higher applied normal loads led to increased wear rates and friction coefficients, whereas with increasing sliding speed, the wear rate was reduced. Major wear mechanisms observed were abrasive, adhesive, plastic deformation, oxidation, and fatigue wear along with delamination.