Fabrication of In-Situ Al–Cu Intermetallics on Aluminum Surface by Friction Stir Processing

Abstract

In-situ Al–Cu intermetallic metal matrix composites (MMCs) surface layer has been fabricated on an A 1050-H24 aluminum plate by friction stir processing (FSP). Pure Cu powder of \({5{\rm \mu}}\)m in size was packed into a groove cut on the aluminum plate and covered with an aluminum sheet. A FSP tool of square probe shape, rotated at a rate of 750–1500 rpm, was plunged into the plate through the cover sheet and the groove and moved along the groove at traveling speed of 0.83 and 1.66 mm/s. Double and triple passes were applied. After the surface MMCs were fabricated on the Al plate, the type and homogeneity of the distributed particles inside the Al matrix have been evaluated from the macro-/microstructure and hardness distribution. As a result, it was found that the copper particles reacted with the aluminum matrix at almost all the processing conditions even during the first pass. Also, at a traveling speed of 1.66 mm/s, most of the resulted intermetallics were CuAl2 at a rotation speed of 750 rpm, while the Cu-rich intermetallics (Al–Cu and Al4Cu9) appeared at rotation speeds of 1000 and 1500 rpm. Moreover, when the traveling speed was decreased to 0.83 mm/s, the amounts of the resulted intermetallics were increased. At a rotation and traveling speeds of 750 rpm and 0.83 mm/s, respectively, the nugget zone matrix consisted of nano-sized CuAl2 intermetallics distributed in aluminum which increase the hardness to almost five times of the aluminum matrix adjacent to the nugget zone.