Fabrication of composite modified layer on aluminium alloy by surface mechanical nano-alloying combined with nitriding

Abstract A composite modified layer was fabricated on 6061 aluminium alloy by means of surface mechanical nano-alloying treatment (SMNAT) combined with nitriding treatment. The microstructure, mechanical properties and interfacial bond of composite modified layer were investigated systematically. The experimental results showed that a Fe coating with thickness of 40–65 μm could be fabricated on the surface of 6061 aluminium alloy by means of SMNAT for 1 h. The mean grain size of top surface layer in Fe coating is about 15 nm. After nitriding, a composite modified layer was generated and its microstructure is depended on the nitriding temperature. The phase structure of modified layer on samples after nitriding at 450 °C, 550 °C and 640 °C is Fe2-3N/Fe(N), Fe2-3N/Fe(N) and Fe2-3N/Fe2Al5, respectively. The properties measurements showed that the surface hardness of 6061 aluminium alloy was greatly enhanced by SMNAT combined with nitriding treatment. The hardness increased with increase of nitriding temperature. Additionally, the mechanical properties match and interfacial bond strength of layer-substrate on the N450 and N550 samples is better than those on the N640 sample. This paper offers a novel method to prepare a gradient modified layer on aluminium alloy for improving surface properties.