Novel Ce thin-film covering on a Mn-Ce-P conversion coating for excellent corrosion resistance of LZ91 alloy

Abstract

Mg alloys exhibit an excellent strength-to-weight ratio, have favorable electromagnetic shielding characteristics, and are biocompatible. Alloying Mg with Li can further reduce weight and enhance ductility along with toughness. Unfortunately, Mg-Li alloys are susceptible to corrosion, which can potentially lead to disastrous material failure. Hence, developing an effective and environmentally friendly anticorrosion treatment is essential. In our previous study, we found that a Mn-Ce-P conversion coating can protect the LZ91 Mg alloy surface from corrosion and enhance its stability in an acidic bath. However, the Mn-Ce-P conversion coating may have cracks and lower corrosion resistance than the Mn-Ce coating; hence, a fast, compact, environmentally friendly, room-temperature Ce conversion coating method was developed for use as a two-step treatment for the Mn-Ce-P conversion coating. Specimens were produced, and the coating microstructures were observed through SEM and TEM; the composition was then analyzed with EDS and X-ray photoelectron spectroscopy. EIS and a salt spray test were performed to quantify corrosion resistance. The two-step coating greatly improved the corrosion resistance; following 72 h exposure to salt spray test, the corrosion area was smaller than 3 %.