Irradiation assisted corrosion of cast A360.1 and additively manufactured AlSi10Mg aluminum alloys in seawater environments
University of New Brunswick
This thesis seeks to compare the effects of irradiation in seawater solution on the corrosion of aluminum alloys produced using casting technique and additive manufacturing. Alloys of aluminum have been deployed as one of the basic materials (such as electrical insulation, scaffolding, and thermal columns) in the containment building of nuclear-powered systems. Thus, they are exposed to various ionizing radiation degrees, which tends to affect their corrosion behavior. The aluminum samples were irradiated with a gamma-ray while at the same time exposed to seawater solution to study the effect of radiation on corrosion. Nuclear irradiation influences the corrosion and surface reactions of metals by altering their properties and/or by changing the composition of the immersed solution. A gamma-ray from a four (4) µCi-Co-60 source was transmitted through a 7 mm hole that served as a window into the corrosion test cell used for gravimetric analysis containing seawater at room temperature with a pH of 8.20 without any buffer. This experimental setup allowed radiolysis and corrosion to occur on the sample's surface in contact with the seawater environment. Samples were irradiated for 24, 72, 144, 240 hours. The formation and composition of the oxide were carried out by utilizing scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), Raman Spectroscopy, and X-Ray Diffraction (XRD) techniques. Ionizing radiation disintegrates water to create oxidizing (OH, O₂, H₂O₂) and reducing (e[superscript]-, H*, and H₂) chemical species. These radiolysis species react with disintegrated solutes and partake in surface reactions prompting a critical change in the redox condition and may form solid species. Seawater contains various solutes; dissolved solutes' presence affects the constant state concentration of molecular water radiolysis species by rivaling radical species. In any case, the relative increment noticed comparatively with purified water relies on the concentration of solute and pH. Weight changes for the Al alloys exposed to seawater solution have been obtained and recorded for 240 hours. The most prominent feature of the results obtained is the difference between the irradiated and the non-irradiated. The irradiated cast A360.1 Al alloy gained weight, while the irradiated additively manufactured (AM) AlSi10Mg lost weight. Similar behavior was experienced in the non-irradiated samples, but the weight changes in radiation presence were more remarkable than those in the absence of radiation. It was observed that the weight changes of irradiated samples increased initially and then leveled off as exposure continued. The irradiated AM samples' standard error measurements appeared much more significant than those of the cast ones. Keywords: Additive manufacturing; Aluminum alloys; Gamma radiation; Corrosion; Microstructure; Gravimetric analysis; Gamma-ray energy spectrum.