Microstructural and tribological characterization of an A-356 aluminum alloy superficially modified by laser alloying

The microstructure and wear of an A-356 aluminum alloy superficially modifi ed by laser alloying were studied. A 2000-W Nd-YAG laser was employed for a lloying a powder composed of 96 wt.% WC, 2 wt.% Ti and 2 wt.% Mg at differe nt traverse velocities of 100, 200, 300 and 400 cm min(-1). Optical (OM) an d Scanning Electron Microscopy (SEM) were used to examine the morphology an d microstructure of the sample surfaces and laser melting zones (LMZ). Wear properties were studied under a load of 5 N by using the ball-on-disc trib ometer. The static partners were balls of 6 mm in diameter made of 52100 st eel. Friction coefficients as well as wear volumes are reported. X-Ray mapp ing of the wear surfaces was used to establish the wear mechanism. It was s hown that, under the conditions in which the wear test was performed, laser alloying of the sand cast Al-356 alloy with WC particles has improved cons iderably the wear resistance of the substrate. The WC particles serve as lo ad-carrying particles and have a severe abrasive action on the steel counte rpart contributing to the steel transference onto the laser treated surface . As the particle size of these carbides decreases, due to a higher interac tion time of the laser beam with the substrate, the wear mechanism changes and the aluminum matrix takes part in the transference process, i.e. some o f the material from the laser-treated surface transfers to the steel ball. Even in this latter case, the laser-treated surface has a better wear resis tance than the substrate. The results were correlated to the roughness, mor phological and microstructural characteristics in each case. (C) 2000 Publi shed by Elsevier Science B.V. All rights reserved.