• Karpasand, Farshid
• Abbasi, Alireza
• Ardestani, Mohammad

Abstract

<jats:p>Al7075/B<jats:sub>4</jats:sub>C surface composites were fabricated by friction stir processing using four passes. The B<jats:sub>4</jats:sub>C powders were added into the prepared grooves with 1 and 2 mm width at the surface of Al7075 alloy in two different manners. In the first one, the B<jats:sub>4</jats:sub>C powders were added prior to the four consecutive passes in one stage. In the second manner, the powders were added in two stages, prior to the first pass and following the second one. The microstructural evaluations showed that the increase in the volume fraction of reinforcement significantly reduced the matrix grain size. Meanwhile, the reinforcement had a more homogeneous and uniform distribution in the samples processed through four consecutive passes. The maximum hardness and wear resistance was achieved in the one-stage powder-added samples, containing higher volume fraction of the reinforcement. A direct relationship was observed between the wear resistance and the composite layer hardness. The wear mechanism in the Al7075 substrate and the non-reinforced friction stir processed sample was the delamination of unstable aluminum oxide tribolayer. However, in the composite samples, a mechanically mixed layer, containing aluminum, chromium, and iron mixed oxides was formed along with B<jats:sub>4</jats:sub>C on the worn surface. In the two-stage powder-added samples, containing lower amounts of reinforcement, the detachment of mechanically mixed layer resulted in three-body abrasive wear condition and high friction coefficient. However, the most stable mechanically mixed layer was formed on the surface of the one-stage powder-added sample containing higher amounts of B<jats:sub>4</jats:sub>C.</jats:p>

Topics

• surface
• grain
• chromium
• grain size
• aluminum oxide
• aluminium
• wear resistance
• composite
• hardness
• positron annihilation lifetime spectroscopy
• Photoacoustic spectroscopy
• iron