Hardness and corrosion behavior of an Al-2Mn alloy with both microstructural and chemical gradients

An Al-2Mn binary alloy with gradient microstructure and chemistry near its surface was fabricated by combining surface mechanical treatment and post-ageing treatment. TEM results indicate that the minimum grain size of the topmost surface layer is below 100 nm. As revealed by SIMS results, Mn is depleted in the surface layer with similar to 2 mu m in thickness, which is due to the "short-circuit" diffusion along grain boundaries and dislocation pipes. Microhardness and corrosion testing results revealed that both hardness and corrosion resistance increase substantially with this gradient design. XPS and Mott-Schottky results demonstrate that the oxide film of the gradient Al-Mn alloy is thinner and denser than that of the coarse-grained sample. Our design method of obtaining gradient distribution both in microstructure and chemistry near metal surface lights a pathway for overcoming the trade-off between properties such as strength and corrosion in 3000 series Al alloys.