Cavitation erosion and corrosion behaviour of laser surface alloyed MMC of SiC and Si3N4 on Al alloy AA6061

Laser surface alloying of SiC/Si3N4 on AA6061 aluminium alloy was carried out using a 2-kW CW Nd-YAG laser. Different ratios of SiC and Si3N4 powders were mixed and the layers were preplaced by pasting. Subsequent laser surface melting of the layers gave a surface metal matrix composite (MMC). The microstructure, chemical compositions and phase identification of the modified layers were examined using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffractometry (XRD), respectively. The laser surface alloyed MMCs of AA6061-SiC and AA6061-Si3N4 consisted of small amounts of Al4C3/Al4SiC4 and AlN, respectively. For specimens alloyed with 100% Si3N4 (AA6061-Si3N4), the cavitation erosion resistance R-e was improved by three times as compared to the AA6061 alloy whereas there was no significant improvement in R-e of the specimen alloyed with 100% SiC (AA6061-SiC). The surface hardness of the specimens alloyed with SiC/Si3N4 was increased seven times. All the laser alloyed specimens with SiC/Si3N4 showed a decrease in pitting resistance and absence of passivity owing to the aluminium-ceramic interfaces, which favour pit initiation or hindered passivity. (C) 2000 Elsevier Science S.A. All rights reserved.