Corrosion of Linear-Friction-Welded AZ91 and AZX912 Mg-Al Alloys

Abstract

The corrosion performance of the AZ91 and AZ91+2%Ca (AZX912) magnesium alloys joined using linear friction welding was investigated. For similar and dissimilar metal combinations – namely AZ91/AZ91, AZX912/AZX912, and AZ91/AZX912, the performance was evaluated by mass loss analysis and the scanning vibrating electrode technique in 1 wt.% NaCl solution. Galvanic behavior between AZ91 and AZX912 was examined by potentiostatic polarization and galvanic current measurements. Approximately 0.3–0.6-mm-thick seamless weld zones were generated in all of the welds, which did not show any appreciable changes in the surface profiles acquired after the corrosion test. The corrosion-induced mass loss rate of the AZ91/AZX912 dissimilar weld was 10% higher than those of the AZ91/AZ91 and AZX912/AZX912 similar welds. The galvanic test indicated that AZ91 and AZX912 were the anodic and cathodic regions, respectively, with a difference in the corrosion potential of 20–30 mV. The corrosion of the AZ91/AZX912 weld was presumed to proceed via a macro-galvanic cell between the base alloys, whereas the weld acted as a bridge and did not influence the corrosion.

Effect of Al and Ca Elements on the Atmospheric Corrosion of Field-Exposed Mg–Al–Zn–Ca–Mn Magnesium Alloys

“…The appearance of gravity-cast AZ91 and AZX912 plates after corrosion testing in a 3% NaCl solution supports this assumption, as the former exhibited intense corrosion pits while most of the surface retained a metallic appearance, whereas shallow filiform corrosion was widespread on the latter. 39 Influence of exposure sites on atmospheric Mg corrosion.-As shown in Table II, Miyakojima has a higher average temperature and a larger amount of incoming sea salts, which suggests a more corrosive environment than Choshi. Elevated corrosion rates in Miyakojima compared to Choshi have been reported for carbon steel, weathering steel, Zn, Cu, SUS304, 40 and Al alloys.…”