EFFECT OF A SCANDIUM ADDITION ON ANODIZING AlMg ALLOYS

Abstract

Scandium (Sc) is known to be one of the most effective alloying elements of aluminum alloys. The only drawback is its high price, but that could change quickly due to the promising results of recent research on its extraction. However, the data on how it affects anodic oxidation are very scarce. In this research, we analyzed how a micro-addition of Sc to the AlMg alloy affects the growth mechanism and properties of the protective aluminium oxide layer depending on the anodization parameters. For comparison, alloy AA5083 with a similar magnesium content was also anodized with the same anodizing parameters. In all experiments, sulfuric acid (VI) with concentrations of 1.72 M or 2.2 M at temperatures of 21 °C or 35 °C was used as the electrolyte. Potentiostatic (18 V) and galvanostatic (20 mA/cm2) anodizing methods were applied. The results (SED-EDS) show that scandium is uniformly intercalated in the matrix of the oxide layer and decreases its resistivity, which increases the oxide growth rate during potentiostatic anodizing and decreases the pore density and pore diameters during galvanostatic anodizing. Moreover, it increases the mobility of cations through the oxide layer, thus accelerating the oxidation reaction in concentrated sulfuric acid electrolytes. On the other hand, the increased cation mobility considerably increases the sensitivity to the temperature of the electrolyte, which can change the growth mechanism of the oxide layer and thus its morphology.