Effect of fluoride conversion pretreatment time and the microstructure on the corrosion performance of TEOS-GPTMS sol–gel coatings deposited on the WE54 magnesium alloy

Abstract

The main objective of the present investigation was to evaluate the employment of a fluoride-based pretreatment of the WE54 magnesium alloy on the protection-degradation mechanism of TEOS (tetraethylorthosilicate)/GPTMS (glycidoxypropyltriethoxysilane) hybrid sol–gel coatings when in contact with saline environment, giving special attention to the influence of the pretreatment time. The experimental results evidenced that long pretreatment times favoured the formation of a magnesium hydroxyfluoride layer with a higher F/O ratio, which improved the corrosion performance of the sol–gel coatings and the WE54 alloy. However, the presence of undissolved intermetallic particles and Y-rich precipitates on the surface led to structural defects that allowed the corrosive attack to evolute along the immersion time in saline solution.

Keywords

• Magnesium
• Pretreatment
• Coating
• Sol–gel
• EIS
• Corrosion