Impurity and temperature enhanced growth behaviour of anodic aluminium oxide from AA5052 Al-Mg alloy using hybrid pulse anodization at room temperature

Conventional anodic aluminium oxide (AAO) was formed using direct-current anodization from high-purity (99.99%-99.999%) Al foils at low 0-5 °C with a growth rate about 2-3 μm/h. Here, we investigate the greatly enhanced growth behaviour of AAO from AA5052 Al-Mg alloy (96.6%Al-2.6%Mg) at high 25 °C using hybrid-pulse anodization. The Mg-impurity and high-temperature enhanced growth rate of AAO at 25 °C is over three-fold to 9.7 μm/h; it also reduces the average pore size to 32.2 nm from 42.8 nm due to high-activity Mg hydrolysis releasing high Mg(OH)2-formation heat and H2 gas. The unique property of AAO from AA5052 is discussed.