Mechanisms of hydrogen absorption, trapping and release during galvanostatic anodization of high-strength aluminum alloys

The initial growth of a porous alumina layer and the hydrogen absorption during galvanostatic anodization were studied using high-resolution electron microscopy, thermal desorption spectroscopy, and hydrogen microprint technique. The nanostructure of the alumina layer depends strongly on the anodization time. The embryo of pores grows as the thickness of the oxide layer increases, and a porous alumina layer is formed until the voltage reached its maximum value. Eventually, the connected pores to the substrate appear in a steady-state voltage region that acted as hydrogen pathways. The substrate does not show delayed embrittlement after the early and late stages of anodization, which is attributed to the low amount of absorbed hydrogen during the anodization. In the middle stage of the anodization, a higher amount of hydrogen is trapped in the substrate/layer interface and then migrates inward into the alloy when the specimen is subjected to stress resulting in delayed hydrogen embrittlement.