Effect of Mn/Mo incorporated oxide layer on the corrosion behavior of AA 2024 alloy

The oxide layer formed over AA 2024 using 10 wt.% H2SO4 (plain oxide, PO) was modified by Mn/Mo oxyanions (permanganate/molybdate modified oxide, PMMO) as an alternative to Cr(VI) ions to enhance the corrosion resistance. The corrosion current density values obtained for PMMO was found to be 2.8% and 1.4% of hydrothermal treated oxide (HTO) and PO respectively after 168 h immersion in 3.5% NaCl solution. The electrochemical studies showed the higher barrier layer resistance for PMMO. The improved corrosion behavior of PMMO was observed based on the damage function calculated. Similar observations were confirmed by continuous salt spray test.

► Permanganate modified oxide layers were prepared on AA 2024 alloy.
► Plain oxide and hydrothermal treated oxide layers were also prepared for comparison.
► Electrochemical behavior of all the oxide layers was evaluated by various methods.
► Higher barrier layer resistance was obtained for permanganate modified oxide layers.
► Modified oxide layers withstood 168 h of continuous salt spray test.