Development of Al-5%Zn-0.5%Sn-2.6%Mg Alloy as Sacrificial Anode for Cathodic Protection of Steel in 3 wt.% NaCl Solution

Abstract

In this work, two aluminum alloys, Al-5Zn-0.5Sn and Al-5Zn-0.5Sn-2.6Mg, were prepared by melting in an induction furnace to be used as sacrificial anodes for cathodic protection of marine structures. The alloys are characterized by scanning electron microscopy mapping coupled to energy dispersive X-ray analysis, X-ray photoelectron spectroscopy and X-ray diffraction. Afterwards, the corrosion behavior was studied in 3 wt.% NaCl solution through immersion tests, potentiodynamic polarization, electrochemical impedance spectroscopy and weight-loss measurements. Results display that active dissolution of Al-5%Zn-0.5%Sn-2.6%Mg alloy and its quasi-uniform corrosion is associated with the major precipitates MgZn2 and Mg2Sn particles formed during the melting process. Galvanic coupling measurements over 45 d were carried out on both alloys. The sacrificial cathodic protection of both anodes was successful but the couple efficiency was greater for Al-Zn-Sn-Mg owing to its more negative corrosion potential and uniform dissolution.

Effect of backfilled stone/brine media on the initial electrochemical performance of aluminum sacrificial anode

“…[5,29] The high-frequency capacitive loop can be attributed to the charge transfer process of the electric double layer at the electrode/electrolyte interface, related to the charge transfer phenomenon and the oxide film effect of the Al anodes. [4] The low-frequency capacitive loop may be related to a dissolution-redeposition process from In (or Zn and Sn) ions [6,28,29] and the adsorbed product layer on the anode surface. [5] The inductive loop in the intermediate frequency range can be attributed to the adsorbed species, [5] probably corresponding to the pitting of the Al anode.…”

“…In addition, the alloying elements in the Al anode are cathodic phases to form microgalvanic cells, resulting in the local breakdown of the surface film and subsequent local dissolution of the Al substrate. [4,5,28] These zones enriched in alloying elements are usually the weak points in the oxide layer, which can be attacked by Cl − in the brine to initiate corrosion pittings on the Al alloy surfaces. [27] Moreover, Zn, In, and Sn in the anode are the so-called activation elements to improve its active dissolution according to a dissolution-redeposition process.…”

“…Aluminum (Al) alloy sacrificial anodes have been widely used to protect marine structures due to their high current efficiency, low specific weight, and low cost. [1][2][3][4][5] They usually work in the seawater at different depths [6][7][8][9][10] or sea mud, [11][12][13] displaying different electrochemical performances due to different media features, such as temperature, [14][15][16] hydrostatic pressure, [6][7][8][9][10] dissolved O 2 (DO) content, [14] pH, [17] and sulfate-reducing bacteria (SRB). [13,18,19] Nowadays, steel shell-concrete composite structure has been adopted for subsea immersed tunnels, typically buried in backfilled stone layers up to several meters thick and hundreds of kilograms per unit, as shown in Figure 1a.…”

Effect of backfilled stone/brine media on the long‐term free corrosion and electrochemical performance of an aluminum sacrificial anode

“…where S is the anode's working area (m 2 ) and t is the immersion time (h). The v loss can be transferred to v d (mm a -1 ) as [16] :…”

Evaluating the Performance of Aluminum Sacrificial Anodes with Different Concentration of Gallium in Artificial Sea Water

“…Specifically, the current efficiency of the 4# sample is the best, reaching 98.25%. It can be compared with the bibliographical references that state the current efficiency of Al-Zn-In alloys are around 70 to 90% [33][34][35][36].…”