EROSION AND CORROSION CHARACTERISTICS OF AN ALUMINUM-ALLOY ALUMINA FIBER-COMPOSITE

The present paper describes the erosion-corrosion behaviour of an alum inium alloy (BS: LM 5) and its composite containing 10 vol.% alumina f ibres. Tests were performed in 3% NaCl solution with and without sand particles (10 wt.%) using the rotating sample method. Salt immersion a nd potentiodynamic polarization studies of the specimens were also car ried out in 3% NaCl solution. Both the tests showed increased weight l oss with test duration. The composite suffered from more material loss than the base alloy. The erosion-corrosion test revealed a significan tly higher extent of weight loss in the specimens as compared to the i mmersion test in an identical electrolyte (3% NaCl). Corrosion of the samples proceeded by the breaking-off of the oxide layer followed by n ucleation of micropits and crater formation. Further, the composite su ffered from additional attack by the electrolyte at the dispersoid-mat rix interfaces. The potentiodynamic study indicated only a nominal shi ft in the corrosion potential of the composite, while a considerable i ncrease in the corrosion current density of the base alloy was observe d due to the incorporation of Al2O3 fibres. The presence of the alumin a fibres in the matrix alloy increased the susceptibility of the compo site towards pitting (at the fibre-matrix interface). In erosion-corro sion tests, weight loss of the samples was accelerated by the impingem ent of the electrolyte at corroded sites leading to easy removal of co rrosion products from the surface. The presence of sand particles in t he electrolyte further accelerated the process of material removal due to rapid formation of pits and craters and (partial) removal of alumi na fibres from the surface. Four stages of erosion-corrosion, namely ( 1) incubation period, (2) accelerated erosion-corrosion, (3) decelerat ion period and (4) steady state material loss, were observed during th e erosion-corrosion tests.