Fabrication of Al/AlN nano-composite layers by friction stir processing of 6061 Al-T6 substrate

Abstract

Friction stir processing was employed for the production of Al/AlN nano-composite layers on a 6061 Al-T6 substrate. Nano-sized AlN powder was inserted in a groove in the middle length of the substrate. Defect-free layers were achieved using tool rotation and substrate advancing speeds in the range of 900–1400 rpm and 63–310 mm/s, respectively. Subsequent passes were conducted to break-up AlN clusters that formed in a non-uniform fashion after initial pass. The grain size of aluminum matrix was found to decrease by the introduction of AlN powder. A nano-composite layer with near uniform dispersion of nano-sized AlN reinforcements with a ~9.6% volume fraction was achieved in a matrix of fine dynamically restorated Al grains with a mean size of ~2.5 µm after three subsequent passes. This layer showed an average micro hardness value of ~164 HV (much greater than ~103 HV of the underlying substrate). In addition, the nano-composite layer exhibited superior dry sliding wear performance against hardened steel compared to that of 6061-T6 substrate. Increasing tool rotation and substrate advancing speeds were found to decrease the AlN content of the processed layer possibly due to increasing in powder scattering by the pin tool. This was associated with a decrease and increase in hardness values and wear-loss data, respectively. Copyright © 2014 John Wiley & Sons, Ltd.