Laser surface alloying of silicon into aluminum casting alloys

Abstract

Aluminum alloys that are easily castable tend to have lower silicon content, and hence, lower wear resistance. The use of laser surface alloying to improve the surface wear resistance of 319 and 320 aluminum alloys was examined. A silicon layer was painted onto the surface to be treated. A high power pulsed Nd:yttrium–aluminum–garnet laser with fiber-optic beam delivery was used to carry out the laser surface treatment to enhance the silicon content and produce a very fine silicon-rich phase. One advantage of using a pulsed laser beam to carry out the surface alloying is it provides a vigorous turbulence in the molten pool and enhances the dissolution of the fine silicon into the molten bath and its dispersal in a short process time. Process parameters were varied to obtain smooth single treated tracks and minimize the surface roughness from overlap of the treated tracks. Our goal is to take advantage of the vigorous turbulence characteristic of the pulsed beam to obtain desired microstructure of laser-alloyed layers, and at the same time to employ the pulse parameters that mimic continuous wave operation as closely as possible to produce the smooth surface. The surface-alloyed layer was characterized and the silicon content and microhardness profile were determined.