Abstract
One of the main ways to protect steel against corrosion is by the galvanizing process. This process has been continuously developed and its first optimization was performed by the addition of Aluminum in the coating. As a result, Zn-5wt.%Al and 55wt.%Al-Zn coatings were developed. Recently, the search for increased corrosion resistance led to the development of zinc coating with the addition of magnesium and aluminum. In this work, a comparative study of the corrosion resistance of zinc coated steel and Zn-2wt.%Al-1wt.%Mg alloy coated steel was performed. Samples were exposed to immersion corrosion tests in 0.1 M NaCl electrolyte and were analyzed by using SEM, XDR and EIS. On zinc-coated steel, the steel substrate was attacked after 48 days of immersion, while on Zn-2wt.%Al-1wt.%Mg coated steel, the steel substrate showed corrosive process after 90-day of immersion. The corrosion product formed from Zn-2wt.%Al-1wt.%Mg coated steel is the main cause of its better corrosion resistance compared to zinc coated steel.
Highlights
In order to improve corrosion resistance and reduce costs of galvanized steel sheet, great efforts have been invested into optimization of the zinc coating composition by alloying.The zinc coating provides corrosion protection to steel by cathodic protection
The coating compositions were measured by inductively coupled plasma optical emission spectrometry (ICP-OES) and coating thickness were measured by scanning electron microscopy (SEM) micrograph
It was concluded that Zn-Al-Mg coating showed higher corrosion resistance than Zn coating in 0.1M NaCl solution immersion test
Summary
In order to improve corrosion resistance and reduce costs of galvanized steel sheet, great efforts have been invested into optimization of the zinc coating composition by alloying.The zinc coating provides corrosion protection to steel by cathodic protection. In order to improve corrosion resistance and reduce costs of galvanized steel sheet, great efforts have been invested into optimization of the zinc coating composition by alloying. In addition to the galvanic protection, the insoluble zinc corrosion products formed on the surface in atmospheric conditions assure a barrier effect (Yoo et al, 2014). The composition of those corrosion products depends on the exposure conditions and this protection is not observed in all environments (Volovitch, 2009; Prosek, 2008; Hosking, 2007; Le Bozec, 2013; Salgueiro, 2015). In the last twenty years, a large effort has been made in order to improve the corrosion resistance of zinc coatings without increasing its thickness or resorting to additional corrosion protection such as protective layers. The main development activity is focused on Zn-Al-Mg coatings
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