Investigation of the Combined Effects of Temperature and Humidity on Fracture Behaviour of Al-Mg-Si-Mn Alloys: Implications in the Coastal Region

Abstract

Aluminium alloys have been integral to numerous engineering applications due to their favourable strength, weight, and corrosion resistance combination. However, the performance of these alloys in coastal environments is a critical concern, as the interplay between fatigue crack growth rate and fracture toughness under such conditions remains relatively unexplored. The combined effect of interdependencies between temperature and humidity under localised corrosion on the fracture toughness of aluminium alloys has not been extensively studied. Little attention has been paid to this phenomenon due to the challenge in understanding its behaviour, and the difficulty in predicting the effect of these factors on fracture behaviour. Therefore, the present study aims to address this knowledge gap and improve the understanding of the interdependencies between the coupled effects of temperature and humidity on the fracture toughness of Al–Mg–Si–Mn alloy. This research can have practical implications for selecting and designing materials in coastal environments. Fracture toughness experiments were carried out by simulating the coastal environments, such as localised corrosion, temperature, and humidity, using compact tension specimens. The fracture toughness increased with varying temperatures from 20°C to 80°C and decreased with variable humidity levels between 40% and 90%, revealing that the Al–Mg–Si–Mn alloy is susceptible to corrosive environments. Using a curve-fitting approach that mapped the micrographs to temperature and humidity conditions, an empirical model was developed, which revealed that the interaction between temperature and humidity was complex and followed a nonlinear interaction supported by microstructure images of SEM and collected empirical data. The fatigue crack growth rate (FCGR) of aluminium alloys under the combined influence of temperature and humidity remains a relatively unexplored area, receiving limited attention due to its challenges in predicting the combined effect of these factors. The challenge was to investigate and address the specific mechanisms and interactions between temperature and humidity, as in coastal environment conditions, on the FCGR of aluminium alloy. The fatigue pre- ii cracked compact tension specimens were corroded for seven days and then subjected to various temperature and humidity conditions in a thermal chamber for three days to simulate coastal environments. The obtained data were analysed to determine the influence of temperature and humidity on the FCGR of Al-Mg-Si-Mn alloy. An empirical model was also established to precisely predict fatigue life cycle values under these environmental conditions. The correlation between fatigue life cycles and fracture toughness models was also examined. The Al-Mg-Si-Mn alloy exhibits a 34% increase in the Paris constant C, indicating reduced FCGR resistance due to elevated temperature and humidity levels. At the same time, fatigue, corrosion, moisture-assisted crack propagation, and hydrogen embrittlement lead to a 27% decrease in the threshold stress intensity factor range. The developed model exhibited accurate predictions for fatigue life cycles, and the correlation between fracture toughness and fatigue life cycles showed less than 10% error, indicating a strong relationship between these parameters.