Effects of phosphorus content on corrosion behavior of trivalent chromium coatings in 3.5 wt.% NaCl solution

Chromium coatings were electrodeposited from trivalent chromium sulfate based electrolyte, containing sodium hypophosphite as a complexing agent. The effects of this agent on morphology, composition, deposition rate, and corrosion behavior of coatings were investigated. Results indicated that, the addition of (0.0–0.75 M) sodium hypophosphite to the electrolyte: 1) resulted in co-deposition of chromium with (12.0–17.4 wt.%) phosphorus; 2) decreased the deposition rate from 17.0 μm/h for Cr–C to 7.8 μm/h for Cr–17.2 wt.% P coatings; 3) deteriorated the corrosion performance of the coatings due to an increase in micro-crack density and porosity. However, the addition of (0.45 M) sodium hypophosphite to the trivalent chromium chloride based electrolyte, decreased corrosion current density of electrodeposited coatings from 2.8 to 1.4 μA/cm2.