Comparing three strategies for surface treatment of Mg coated by hexamethylene diamine tetra methylene phosphonic acid for corrosion protection

Manufacturing Mg and Mg-based alloys with controllable degradation rate has always been a challenge. Surface modification is one of the best ways to acquire protection against corrosion. Previously, many approaches such as phosphating (Na 3 PO 4 ), fluoridation (HF), and alkalization (NaOH) treatments have been used to regulate the corrosion rate. Here, we compare the corrosion rates of 3-surface modified Mg samples coated with hexamethylene diamine tetra methylene phosphonic (HMDTMPA). The protection of those different layers was ranked in the order: phosphate > alkaline > fluoridation treatment. The chemistry of those chemical conversion layers was discussed in the light of scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The mechanism of tailoring a protective film of HMDTMPA on phosphated Mg was discussed according to the ability of P to bridge the substrate with the coating.