Functionally Gradient Coating of Aluminum Alloy via In Situ Arc Surface Nitriding with Subsequent Friction Stir Processing

Functionally gradient coating on the AA6082-T6 substrate is successfully fabricated to improve the wear resistance via in situ arc surface nitriding with subsequent friction stir processing. Under the thermal effect of the arc, the nitrogen is ionized and acutely reacted with the liquid Al, achieving a 600 µm thick nitriding coating. The severe stirring smashes the nitride dendrites into small particles and attribute to the dispersion strengthening layer, which obtains the functionally gradient coating with the microhardness ranging from 140 to 90 Hv. The dispersion strengthening of the refined AlN particles increases the lubricating effect, and decreases the coefficient of friction from 0.5 to 0.15. The wear track and depth of the functionally gradient coating is wider and shallower compared with the AA6082-T6 substrate. The functionally gradient coating transforms the adhesive wear of the AA6082-T6 substrate to the abrasive wear, and then improves the wear resistance significantly. These findings demonstrate that the strategy to construct a functionally gradient coating remarkably improves the wear resistance, which satisfies the applications in the fields of aerospace and automotive.