Influence of Additive on Structure and Corrosion Resistance of Manganese Phosphate Film on AZ91 Magnesium Alloy

Abstract

Manganese phosphate conversion coating was prepared by adding addition agent towards phosphate bath. The structure was investigated using SEM/EDX, and the anti-corrosion performance was evaluated by electrochemical technique. It was found that the film presented in crystal structure, and the crystalloid grain transformed from large grain toward small particles upon the addition. The corrosion resistance was studied by polarization curves and EIS in 3.5%NaCl. Polarization curves showed that the corrosion potential of the coating shifted remarkably towards positive direction comparing with that of AZ91 substrate. EIS results indicated that the radius of the capacity impedance for phosphate film increased distinctly, which validated the excellent anti-corrosion performance of the film.

Biocompatible strontium-phosphate and manganese-phosphate conversion coatings for magnesium and its alloys

“…have also been also adopted by other researchers for corrosion protection purposes (Huan et al, 2012;Zhou et al, 2008Zhou et al, , 2011. However, little research work has been carried out to exploit their biomedical applications, regardless what the underlying metals are, which might be attributed to the safety concerns of the presence of multi-valent Mn (VII and V) cations in addition to divalent Mn cations.…”

“…Though the beneficial effects of Sr on bone regeneration are clear, to date there are few studies exploring the effect of Sr-coated Mg-based biomaterials either on inhibiting biodegradation or osteointegration except for the latest work carried out by Chen et al (Chen et al, 2014;Ke, Pohl, Birbilis, & Chen, 2014), where a biocompatible Sr phosphate (SrPO 4 ) conversion coating was fabricated through a simple wet-chemical conversion technique to significantly restrict the initial degradation of Mg. Han et al (Han, Zhou, Shan, & Ke, 2003) and Zhou et al (Zhou, Shan, Han, & Ke, 2008;Zhou, Tang, Zhao, Wu, & Han, 2011) reported a manganese hydrogen phosphate (MnHPO 4 ) conversion coating for AZ31D and AZ91D alloys and proposed a mechanism of coating formation. Han et al (Han, Zhou, Shan, & Ke, 2003) and Zhou et al (Zhou, Shan, Han, & Ke, 2008;Zhou, Tang, Zhao, Wu, & Han, 2011) reported a manganese hydrogen phosphate (MnHPO 4 ) conversion coating for AZ31D and AZ91D alloys and proposed a mechanism of coating formation.…”

The Formation Mechanism and Corrosion Resistance of a Composite Phosphate Conversion Film on AM60 Alloy

“…PCCs on Mg alloys have been investigated widely [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Phosphating has always been carried out in the acidic solution containing Mn 2+ , Zn 2+ , Ca 2+ , Na + , and Mg 2+ [ 13 ].…”

“…However, the dissolution of the flake particles into small chipping occurred after being immersed in the simulated body fluid for 2 h [ 9 ]. Zhou et al prepared a Mn PCC, the corrosion potential ( E corr ) and the radius of the capacity impedance of which increased distinctly in 3.5 wt % NaCl solution compared with that of the AZ91 substrate, displaying excellent anticorrosion performance [ 8 ]. Chen et al [ 12 ] pointed out that Mn PCC had desirable corrosion resistance, which was more stable and corrosion resistant than its Zn and Ca peers.…”

Corrosion protection of magnesium and its alloys by metal phosphate conversion coatings

“…Although a variety of different theories were proposed to assist in the development of protective conversion coatings, a universally applicable and reproducible coating technology to replace chromate based coatings is still needed. For instance, Han and Zhou [14][15][16] proposed that manganese hydrogen phosphate (MnHPO 4 ) conversion coating initiates on the second phase of the AZ31D alloy, but then rapid growth of this coating takes place preferentially over the surface of the Mg matrix. In contrast, Cui et al 17 claimed a different coating formation mechanism in which a MnHPO 4 film develops exclusively from the nuclei initially formed on the second phase.…”