STRESS-CORROSION CRACKING BEHAVIOR OF SOME ALUMINUM-BASED METAL-MATRIX COMPOSITES

This paper deals with the study of the corrosion behaviour of MMCs wit h AA 6061 or AA 2014 aluminium alloys as matrixes, under the combined action of a sustained elastic tensile stress and a corrosive environme nt, namely 3.5% NaCl solution. Such behaviour was compared with that e xhibited by the corresponding matrixes. Gravimetric corrosion rates we re evaluated after alternate exposures to 3.5% NaCl salt spray or to 3 .5% NaCl solution. Micrographs of specimen sections obtained by the sc anning electron microscope after the alternate exposure tests indicate d the onset of stress corrosion cracking on both the AA 6061 matrix an d the Al2O3p-reinforced AA 2014 composite. Electron Probe Microanalysi s on the crack and pit surfaces and on the material bulk gave a contri bution to determine the cause of the corrosion damage. An attempt was also done to apply the electrochemical noise analysis to evaluate the susceptibility of the various materials to stress corrosion cracking, during continuous immersions in 3.5% NaCl solution, in the presence of stress applied. The results were compared with those obtained with un stressed specimens. The tensile stress produced an increase in the cor rosion rate which was clearly detected by the noise analysis. However, the concomitant presence of pitting (and in some cases of intergranul ar corrosion) and stress corrosion made difficult to distinguish betwe en specimens suffering from the various localized corrosion forms. (C) 1997 Elsevier Science Ltd.