Effect of ion irradiation on aluminium hydroxide on an Al-Mg-Si alloy

As many components of the core of water-cooled nuclear research reactors (NRR) are composed of aluminium alloys, the corrosion study of these alloys is important for their safe and efficient operation. In particular, in the reactor core, irradiation defects created by the rapid neutron flux can have a detrimental effect on corrosion of aluminium alloys increasing thickness of corrosion layers. In order to better understand the effect of irradiation defects on aluminium corrosion, a hydroxide obtained by corrosion of an Al-Mg-Si alloy is irradiated with Al ions at the JANNuS facility at CEA (French Atomic Energy Commission) of Saclay. Al ions with successive energies of 1.2 and 5 MeV are used in order to have a homogenous damage profile in the hydroxide. A TRIM calculation indicates the damage is on average 2.5 dpa (displacement per atom) in the aluminium hydroxide. Various characterization techniques are used to study the impact of ion-irradiation on morphology and crystallography of the aluminum hydroxide. Before ion irradiation, grazing incidence X-ray diffraction and Raman analysis indicate the corrosion product are composed of bayerite (α-Al(OH3)) and pseudo-boehmite (AlOOH). An observation of the aluminium hydroxide with a Scanning Electron Microscopy (SEM) suggests a hydroxide grain size between 1 and 4 µm. After irradiation, X-rays diffraction indicates bayerite is still present but an amorphization of this crystalline phase can be observed. In addition, an observation of a cross section of the irradiated hydroxide with a Transmission Electron Microscopy (TEM) suggests the irradiated hydroxide contains nano-sized crystallites and bubbles. Identifying the phase of these crystallites and the amorphisation process will enable a better prediction of the expected hydroxide thicknesses in core. The results from this work are compared to those obtained after neutron irradiation in order to assess the relevance of ion-irradiation in understanding corrosion behavior of aluminum components in NRRs.