ROLE OF PASSIVATING OXIDE FILM IN THE CORROSIVE WEAR OF AL-7-PERCENT-SI ALLOY

Abstract

The present work examines how passivating oxide film affects the corrosive wear rate of Al-7%Si alloy in H2SO4 solution at room temperature. As the applied potential (relative to a saturated calomel electrode (SCE)) increases to 1.08 V(SCE) on an Al-7%Si alloy specimen, the corrosive wear rate increases and then decreases for polarization to higher anodic potentials. The corrosive wear rate W(cw) consists of three factors, namely pure mechanical wear loss W(mech), weight loss W(diss) caused by the corrosion reaction, and an acceleratory-deceleratory contribution W(acc) due to the presence of passivating oxide film. The acceleratory and deceleratory contributions W(acc) arising from compositional change of the passivating oxide film indicate the microcutting and microploughing mechanisms respectively of abrasive wear. The increased W(acc) by application of 1.08 V(SCE) is discussed from the viewpoints of hydration and severe abrading wear action of the passivating oxide film on the Al-7%Si alloy specimen.