Stress Corrosion Cracking in Generic Aluminum Foil Under 3.5% NaCl Solution

Abstract

Recently, there has been an interest in aluminum alloys by many industrial areas as an environmentally-friendly material reducing environment pollution. Now, especially for maritime industries aluminum alloys are in the spotlight for ship construction instead of fiber reinforced plastics (FRP) or even stainless steel. Aluminum alloy ships are fast, lightweight, and exhibit a great load capacity when compared to traditional steel hulls. The Navy’s number one problem is maintenance due to corrosion impact. Annual combined costs of corrosion for army ground vehicles and navy ships range around $6.14B/year. Corrosion impacts the readiness of most Navy systems and is a major factor contributor to life cycle cost. Hence the vision for corrosion technologies is to develop and implement corrosion control and prevention technologies to minimize the impact of material deterioration and maintenance costs. Stress corrosion cracking (SCC) and environment-induced cracking (EIC) has been extensively investigated using various methods to improve performance, designs, and service life for these structures. Present interested research areas are advanced smart coatings technologies for corrosion control and prevention of its effects under sea water and marine environments. With the rapid development of modern technology, foil metals have found applications in a variety of areas. The mechanical behavior of these materials may be different from that of bulk materials due to size effects. Therefore, models and conclusions for bulk characterization might not be applicable when analyzing foil materials. The purpose of this experiment is to describe and examine the susceptibility of aluminum alloy foil to stress corrosion cracking under 3.5% w.t NaCl solution. Mechanical properties of aluminum specimens were investigated using slow strain rate tests of 0.001 mm/min under load control while inside an environmental chamber at a flow rate of 150 ml/min. Smooth specimen samples with thickness of 0.0508 mm were subjected to monotonic tensile tests until fracture in ambient air and under corrosive solution environment. Scanning electron microscopy (SEM) was used to analyze stress corrosion cracking and crack propagation observing the different microstructural and intergranular fracture deformations. A digital microscope camera was used to observe and perform an analysis on the corroded specimen surface. A comparison of stress, strain, and time results of fracture between air and 3.5% NaCl solution at room temperature were calculated to demonstrate the susceptibility of the aluminum material to SCC. Test standards regarding stress corrosion cracking in metal foils are still limited.