The corrosion behavior of ZnAlMg alloys in maritime environments

Abstract

Steel strip with a ZnAlMg coating presents an interesting alternative for use in construction applications in highly corrosive environments. Two ZnAlMg alloys were exposed to the atmosphere in maritime environments in Mexico, China, and Sweden for periods of up to 3 years. The exposure program included specimens fully exposed to the weather at a 45° angle and specimens under shelter at 5°. Parallel to the field exposure a cyclic corrosion test (ISO 16701) was done. After exposure, the specimens were subjected to metallographic (SEM) examination. After 1 year, the rates of corrosion were determined gravimetrically by using a pickling process to remove the products of corrosion. ZnAlMg coatings show a selective corrosion mechanism and improved corrosion resistance compared to pure Zn coatings in every investigated environment.

Long‐term atmospheric corrosion rates of hot dip galvanised steel and zinc‐aluminium‐magnesium coated steel

“…A ratio of improvment between 2.4 and 3.3 was found after two years of exposure. Similar results were found by Tomandl et al after one year exposure in marine and marine tropical field sites. Similar results have been obtained recently by Persson et al…”

Revisión y análisis de la corrosión a largo plazo de recubrimientos basados en aleaciones de Zinc-Aluminio-Magnesio, como alternativa a los recubrimientos tradicionales basados en cinc, para canalizaciones eléctricas

“…• The performance of ZM alloys using rain water electrolyte is much lower than using NaCl. i) Tomandl and Labrenz (Tomandl & Labrenz, 2016), conducted a field test in Sweden, China and Mexico to compare the performance against corrosion between zinc and ZM alloys, in maritime environments. Table 11 shows a summary of all the field tests results, while table 12 shows the accelerated tests results.…”

Analysis of metallic coatings based in zinc-aluminium-magnesium alloys, in terms of performance and long-term corrosion. Case study: Electrical cable trays selection in project design

“…• After all accelerated tests as well as after 2 years of field exposure in 3 different sites, ZM coating with 3 wt.% of Mg and 3.7 wt.% of Al have shown a better corrosion resistance than PG (in terms of weight loss). • "The corrosion behavior of ZnAlMg alloys in maritime environments" (Tomandl & Labrenz, 2016).…”

“…Test 7.1 -Corresponds to the source number 7 (Tomandl & Labrenz, 2016) and the location 1, that corresponds to Bohus-Malmön (Sweden).…”

“…In their study of corrosion of ZM coatings in a marine environment, Tomandl and Labrenz (Tomandl & Labrenz, 2016) observed that ZM coatings adjacent to cut edges were completely consumed within three years at a test site in China and just one year at a test site in Mexico. The authors of this paper concluded that on specimens with a thickness of 2mm, cathodic protection at the cut edges no longer exists after conversion of the layer 2-3mm away from the edge and that according to this evaluation, long-term protection at the cut edges is to be expected only on the specimens from the location with the lowest corrosivity.…”