A novel route for development of Al–Cr–O surface nano-composite by friction stir processing

In this study, friction stir processing (FSP) was used to develop in situ Al–Cr–O hybrid nano-composite on the surface of Al6061 plate. This procedure combines the hot working nature of FSP and the exothermic reaction between aluminum and Cr2O3. A new procedure was introduced for applying the reinforcement particles, in which Cr2O3 powder was applied on Al6061 plate by atmosphere plasma spray (APS), and then the FSP was performed on the plate. During of FSP, due to thermomechanical condition, Cr2O3was reduced by aluminum and as a consequence Cr and Al2O3 were produced. With increasing the number of FSP passes, intermetallic compounds including Al13Cr2 and Al11Cr2 were developed resulting from the reaction between Al and Cr. TEM analysis showed that nano-sized reinforcement particles were distributed in the aluminum matrix. As a result of nano-sized reinforcement particles, the composites possess enhanced hardness and ultimate strength.

► Al–Cr–O nano-composites were fabricated in situ by FSP.
► During FSP, Cr2O3 was reduced by Al and then in situ Al–Cr reactions were induced.
► The size of reinforcing particles formed by in situ reaction is ∼100 nm range.
► Nano-composite after six FSP passes has Al2O3, Cr2O3, Cr, Al13Cr2 and Al11Cr2 in Al matrix.
► The nano-composites are fully dense with improved microhardness (147 Hv) and tensile strength (518 MPa).