Electrochemical treatment of aluminium alloy 7075 in aqueous solutions of imidazolium phosphonate and phosphate ionic liquids and scratch resistance of the resultant materials

The abilitiy of 1-ethyl-3-methylimidazolium ethylphosphonate ([ImPhosphonate]) and 1-ethyl-3-methylimidazolium diethylphosphate ([ImPhosphate]) ionic liquids (ILs) to interact with anodized Al7075 T6 aluminium alloy has been studied via electrochemical techniques under different applied potentials, inside and outside the passivation regions. SEM, EDX and XPS analysis have been used to study the composition of the surface coatings. The abrasion resistance after treatment with the ILs has been studied by scratch tests under progressive load, and compared with the performance of the unprotected material and the anodized alloy. While conventional anodization only improves the abrasion resistance of Al7075 in a 30%, the maximum reduction of the penetration depth, 86% with respect to Al7075 and 79% with respect to the anodized alloy, is obtained for the material treated with [ImPhosphonate] at 1 V, in the passivation region. Under these conditions, a phosphorus-containing alumina layer is formed. Applied voltages outside the passivation region for each IL activate the dissolution of the alumina layer and reduce abrasion resistance, not only with respect to the anodized material, but also with respect to the unprotected alloy.