Evaluation of corrosion resistance of magnesium alloys in radiator coolants

Abstract

Coolant corrosion is a major drawback for the use of magnesium alloys in engine and cooling system, but the coolant is not normally intended to prevent corrosion of magnesium alloys. This research assessed the corrosion performance of two magnesium alloys, AZ91D and AM50A, in two newly formulated radiator coolants using immersion test, potentiodynamic polarisation test, and corroded surface analysis. Two coolants were named as Irgacool Plus L and Irgacool Plus S. C7, C8-organic acids and polycarboxylic acid were the main inhibitor species in Irgacool Plus L while Irgacool Plus S was formulated with C7, C8-organic acids and sebacic acid inhibitors. Corrosion rates of magnesium alloys decreased twice in Irgacool Plus L compared with Irgacool Plus S. AZ91D alloy had better corrosion resistance than AM50A alloy in both radiator coolants. Both alloys suffered corrosion due to microgalvanic coupling between cathodic b-Mg 17 Al 12 intermetallic and anodic a-Mg matrix, and the presence of Al 8 Mn 5 and Al 11 Mn 4 intermetallics in AM50A led to further microgalvanic corrosion. A continuous network of b-Mg 17 Al 12 phase and higher Al content a-Mg matrix accounted for better corrosion resistance of AZ91D alloy.

Electrophoretic Deposition of Nanohydroxyapatite on Homogenized Magnesium Based Alloy for Biomedical Applications

“…These sections are known as the α+β phase containing more aluminum (Al) content than the primary α phase [36]. This network of eutectic combinations with higher Al content contributes to the corrosion resistance which retrains the advance of the corrosion attack [37]. The FESEM microstructural image also revealed large β phase particles and α + β phase components in a fine lamellar combination as presented in Figure 3.…”

Properties of Microplasma Coating on AZ91 Magnesium Alloy Prepared from Electrolyte with and without the Borax Addition

“…Too much additional zinc (over 5%) causes hot brittleness and the formation of microporosity in the alloy, whereas manganese, which is the basic component found in almost all magnesium alloys, does not significantly affect the mechanical properties, but increases the corrosion resistance of magnesium alloys in saltwater, because it limits the negative influence of iron, which is the cause of corrosion [11]. However, Mg can induce the precipitation of secondary Al-Mn and/or β-Mg 17 Al 12 particles, distributed discontinuously in structure and, thus, due to their relatively high cathodic potential, contribute to decreasing the corrosion resistance of the material [12].…”