SURFACE MODIFICATION OF ALUMINUM BY ELECTRICAL-DISCHARGE ALLOYING

Surface modification of aluminum was carried out using a new method na med electrical discharge alloying. Deposition of titanium contained in electrodes and carbon decomposed from hydrocarbon working fluid occur s on aluminum substrates. With an electrode of a Ti-36mass%Al premixed green compact, in situ composite layers mainly consisting of TiC and TiAl are formed. The process makes it possible not only to coat the in situ composite layers with a thickness of 100 mu m within a few minut es but also to obtain different TiC volume ratios by changing the proc ess parameters. The formation of fine dendritic TiC precipitates can b e considered to be a result of rapid solidification during the process . The volume ratio of TiC decreases with increasing distance from the surface, which means that the modified layers are composed of gradient constituents. The hardness close to the surface can be controlled to a value of 3.5-10.5 GPa changing the process parameters, such as the p ulse width and working time.