Protection of AA5083 by a Zirconium-Based Conversion Coating

A chromium-free zirconium-based conversion coating (ZrCC) was prepared on AA5083. The ZrCC improved the corrosion resistance of AA5083 and the adhesion of epoxy resin significantly, the performance of which was much better than that of the commercial chromium-free treatment and close to that of commercial chromate conversion coating (CCC) treatment. The ZrCC displayed a three-layer structure with a thickness of approximately 1.5 μm, including an inner layer at the alloy/coating interface, a thicker middle layer with nodular particles and an outer layer on the top. Formation of the ZrCC proceeded via the stacking of nodular particles layer upon layer, the composition of which was mainly amorphous Na 3 AlF 6 , Zr(HPO 4 ) 2 ·H 2 O, ZrO 2 and AlPO 4 . The ZrCC with the special three-layer structure provided good protection despite the absence of a "self-healing" ability.