Wear and corrosion performance of two different tempers (T6 and T73) of AA7075 aluminium alloy after nitrogen implantation

Abstract

The present work reports the improvements in corrosion resistance and tribological properties achieved after Nitrogen ion implantation into aluminium alloy AA7075 subjected to two different tempers, T6 and T73.Nitrogen implantation at a nominal dose of 2×1017ions/cm2 and at an accelerating voltage of 50keV produced an increase of the surface hardness of the alloys up to a 130% in T6 samples and to 190% in T73 samples.The increase in hardness has a very positive effect on wear resistance as indicate the significant reduction of specific wear rate on both tempers (about −75% for T6 and −90% for T73 samples).Similarly, an improvement in corrosion properties of both tempers is confirmed by DC techniques, showing a decrease of the registered current density on potentiodynamic curves, and by the increase of impedance shown by AC techniques.This overall improvement in the alloy performance has been mainly attributed to the formation of a stoichiometric aluminium nitride layer (AlN), identified by XPS and GIXRD.The combination of EXCO immersion tests and electrochemical measurements allowed explaining the effect of AlN layer, which behave as a barrier delaying the onset of corrosion and slowing its progress. However, the implantation do not modified the corrosion morphology which seems to be determined mainly by the heat treating conditions. Thereby, in both tempers the localized attack starts at the intermetallic/matrix interface, but in T6 type specimens the progress of corrosion is clearly intergranular, while T73 specimens show the formation of clusters of small geometrical pits, probably related to the biggest MgZn2 strengthening precipitates.