The electrochemical corrosion characteristics of AZ31 and AZ61 magnesium alloys were analyzed in terms of potentiodynamic tests and electrochemical impedance spectroscopy. The influence of the solution composition and material surface finish was examined also through the analysis of corrosion products created on the samples’ surface after electrochemical measurements in terms of scanning electron microscopy using energy-dispersive spectroscopy. Obtained data revealed the differences in the response of the magnesium alloys to enriched Hank’s Balanced Salt Solution—HBSS+ (with Mg²⁺ and Ca²⁺ ions) and Hank’s Balanced Salt Solution—HBSS (without Mg²⁺ and Ca²⁺ ions). Both examined alloys exhibited better corrosion resistance from the thermodynamic and kinetic point of view in the enriched HBSS+. AZ61 magnesium alloy reached higher values of polarization resistance than AZ31 magnesium alloy in both the used corrosion solutions. Phosphate-based corrosion products were characteristic for the AZ31 and AZ61 alloys tested in the HBSS (without Mg²⁺ and Ca²⁺ ions). The combination of phosphate-based corrosion products and clusters of MgO and Mg(OH)₂ was typical for the surface of samples tested in the enriched HBSS+ (with Mg²⁺ and Ca²⁺ ions). Pitting corrosion attack was observed only in the case of enriched HBSS+.

In this work, the quality of coatings prepared by plasma electrolytic oxidation (PEO) on an AZ31 magnesium alloy were evaluated. This was done by studying the effects of the chemical composition of phosphate-based process electrolytes in combination with different applied current densities on coating thickness, porosity, micro-cracking and corrosion resistance in 0.1 M NaCl. Both processing parameters were studied in four different levels. Mid-term corrosion resistance in 0.1 M NaCl was examined by electrochemical impedance spectroscopy and based on this, corrosion mechanisms were hypothesized. Results of performed experiments showed that the chosen processing parameters and electrolyte composition significantly influenced the morphology and corrosion performance of the prepared PEO coatings. The PEO coating prepared in an electrolyte with 12 g/L Na₃PO₄·12H₂O and using an applied current density 0.05 A/cm² reached the highest value of polarization resistance. This was more than 11 times higher when compared to the uncoated counterpart.

Purpose: The purpose of this paper is to compare electrochemical corrosion characteristics of conventional and unconventional fluoride conversion coating prepared on magnesium alloy. Design/methodology/approach: The chemical reaction of AZ61 with 38 wt.% hydrofluoric acid (HF) for 24 h was used as a conventional way of fluoride conversion coating preparation. The unconventionally prepared coating was created in Na[BF₄] salt melt at 450°C for 2 h. Morphology and chemical composition of prepared fluoride conversion coatings were studied with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical corrosion characteristics of the coatings were analyzed in Hank’s solution using potentiodynamic tests. Findings: Both the coating preparation ways resulted in the creation of uniform conversion coatings with the same thickness (1.3 ± 0.1 μm). Some defects were observed on the coatings surface; however, the defects did not reach the AZ61 surface. Electrochemical tests performed in Hank’s solution at 37°C showed an improvement of corrosion resistance of AZ61 treated with fluoride conversion coatings when compared to the untreated material. Unconventionally prepared coating reached better electrochemical corrosion characteristics when compared to the conventionally prepared coating. Originality/value: Electrochemical corrosion characteristics of AZ61 magnesium alloy can be improved with fluoride conversion coatings. Two methods are used in the literature for the coatings preparation. The conventional method is based on dipping of the coated material to the HF, and the unconventional method lies in dipping of the sample to the Na[BF₄] salt melt. The main purpose of the present study is to analyze the conventionally and unconventionally prepared coatings in terms of chemical analysis, morphology and material corrosion protection (electrochemical corrosion characteristics), while the data are not provided in the literature, according to the authors’ knowledge. Very similar coatings were prepared using both the methods from the morphological and chemical composition point of view. However, unconventionally prepared coating created in Na[BF₄] salt melt reached better electrochemical corrosion characteristics compared to the coating prepared in HF.