Atmospheric Corrosion of Al-Zn Coated Steel Sheets Exposed under Marine Environments in Kenya

Corrosion contributes to multibillion USA dollar loses due to deterioration, weakening and ultimate failure of engineering infrastructure globally necessitating further research to build more corrosion resistant materials. The aim of this study was to investigate atmospheric corrosion of aluminium-zinc coated steel roofing sheets exposed to outdoor marine environment in Kenya at Diani and Mariakani sites, representing severe marine and urban marine environments respectively. Al-Zn coated sheets measuring 130 mm x 190 mm coated with masses ranging from 60-150 gm2 were exposed for 2 years. The specimens were collected at periodic intervals following ASTM G1-90 standard method and corrosion products analyzed by Raman spectroscopy, while corrosion rate was determined by weight loss method. Corrosion rate ranged from 0.03 to 0.05 mmpy and increased with decreasing masses coating materials from 150 to 60 (gm2). Diani site recorded higher corrosion due to severe marine conditions characterized by high chlorides, RH of 81%, UV of 12mW/cm2 and a temperature of 27 ℃. Dominant rust constituents were goethite (a-FeOOH) and lepidocrocite (g-FeOOH), while  ferrihydrite and maghemite (a-Fe2O3) were measured at low levels suggesting the influence of suphur dioxide and chloride pollution on  corrosion rate at both sites. Corossion rates ˂ 0.15 mmpy at both  sites suggest excellent protection by the formulated coating media. The results of this contribute to improving the quality of the AZ metal coating media under marine environments.