Investigation on AC corrosion of aluminum alloy sacrificial anode in the artificial simulated seawater environment

Abstract

The alternating current (AC) density induced by submarine cables, which are parallel to submarine pipelines, has nonnegligible effects on the sacrificial anode system of submarine pipeline. The objective of this work is to clarify the AC corrosion of aluminum alloy sacrificial anode. The weight loss tests show that the corrosion rate of aluminum alloy increases with the increase in AC density, whereas the corrosion pits are obvious and dense. The calculated AC current efficiency for aluminum alloy is obviously higher than that for carbon steel under the same condition. The analyses of polarization characteristics and local environment reveal that the activity of aluminum alloy increases under the combined action of alloying elements and AC interference. Furthermore, the surface characteristics verify that Al and the alloying elements (Zn or In) in the solid solution with aluminum are oxidized during the anodic half cycles of AC density. And the alkaline environment created by the cathodic reaction in the cathodic half cycles is beneficial to the dissolution of aluminum alloy. In the condition of high AC density, the vigorous gas evolution is observed on coupon surface, resulting in the formation of larger corrosion pits due to the intrinsic effects of the adsorbed hydrogen and hydrogen bubbles. These results provide a guidance to understand the mechanism of AC corrosion for aluminum alloy exposed to artificial simulated seawater environment.