This study aims to explain the metallurgical reasons behind the changes in corrosion behavior of AISI 316L austenitic stainless steel (SS) when alloyed with different Cu concentrations of 1%, 2%, 3% and 5% by weight. The Cu-alloyed samples were prepared by melting stainless steel 316L with Cu in a high-purity argon environment, followed by homogenizing at 1100 ℃ for 2 h, cold-rolling, and recrystallising at 1100 ℃ for 30 min. Corrosion behavior was tested in a 0.9 wt.% NaCl solution using a potentiostat-controlled three-electrode cell. The 2 and 3% Cu alloys exhibited lower corrosion rate compared to the other compositions. A detailed examination using transmission electron microscopy (TEM) was conducted specifically on the 2.5% Cu alloy. This analysis provided insights into the structural and compositional changes responsible for the improved corrosion resistance. The addition of 2.5% Cu to 316L stainless steel significantly improves corrosion resistance. TEM analysis shows a stable microstructure with a dendritic austenite matrix, δ-ferrite in interdendritic regions, and M23C6 carbides at phase boundaries and within ferritic grains. Low dislocation density and coherent particles further enhance stability and resistance. These combined microstructural features create a highly corrosion-resistant alloy.