Heliyon (Feb 2024)
Synergistic effect of Mg addition on the enhancement of the mechanical properties and evaluation of corrosion behaviors in 3.5 wt % NaCl of aluminum alloys
Abstract
Aluminum alloys are highly preferred for their superior properties, including high corrosion resistance and lightweight in the automotive industry. To better understand how magnesium addition affects aluminum's corrosion and strengthening properties, three different percentages of magnesium-added aluminum alloys, as well as pure aluminum, were melted at a temperature of 800 ± 10 °C in a furnace and cast using the sand molding process. Subsequently, weight loss was used to conduct corrosion testing along with mechanical tests such as tensile, flexural, hardness, and impact tests. In-depth research revealed that the addition of magnesium at 3 wt %, 5 wt %, and 7 wt % strengthened the aluminum alloy. The addition of magnesium resulted in the formation of Al3Mg2, which restricted the movement of dislocation, induced grain refinement, and increased the strength of the alloy. However, it was observed that the addition of magnesium caused a decrease in the alloy's toughness and ductility, resulting in decreased impact energy and % elongation by 29.19 % and 34.87 % respectively by the addition of 5 wt% Mg compared to pure aluminum. Nevertheless, the optical microstructure and SEM image revealed refined grains and the formation of Al3Mg2, providing valuable insight into magnesium's strengthening behavior in aluminum. The study found that adding 7 wt % Mg to the aluminum alloy did not significantly improve its strength and hardness compared to adding 5 wt % Mg. This was because the 7 wt % Mg addition caused the grain size to increase, making it less effective at resisting dislocation movements. The grain coarsening of the 7 wt % Mg added alloy was also revealed in the optical microscope and the SEM images. The EDS analysis confirmed the presence of Al and Mg within the globular-shaped intermetallic particles, indicating the formation of the Al3Mg2 intermetallic phases. However, the highly reactive nature of magnesium results in a higher corrosion rate in terms of weight loss and corrosion current density, which causes the formation of pits and metal dissolution, leading to significant metal loss beneath the original surface when immersed in 3.5 wt % NaCl medium for a period of fifteen and thirty days. Localized corrosion was indicated by the SEM images, which showed concave and convex structures formed by the corrosion products on the alloys. The breakdown of the Al2O3 protective layer, which is the cause of the pits and cracks in the corrosion products, may be brought on by internal stress or the dehydration of hydroxides, which is known as Mg-induced stress corrosion cracking. However, more pits and cracks are found in the SEM image for the 7 wt % Mg addition as it was corroded more compared to the other alloys. The map analysis of the corroded alloy confirmed the corrosion behaviors of the Mg-added alloy by the presence of oxygen all over the surface. Because of the alloy's Al3Mg2 intermetallic compound's refinement and lower corrosion rate, 5 wt % of Mg was found to be the optimal amount for the addition of aluminum to increase strength and hardness without compromising the alloy's toughness and ductility.
