Investigating the Influence of Li and Sc Addition on the Microstructure and Electrochemical Properties of 7075 Aluminum-Based Alloys

This study investigates the effect of 0.1% scandium (Sc) and 2.2% lithium (Li) additions on the microstructure and electrochemical behavior of 7075 aluminum alloys. Samples were treated in the T6 (120 °C/24 h) and T7 (280 °C/8 h) conditions. Microstructure investigations using scanning electron microscope (SEM) were done to understand the influence of alloying additives on the as-cast and heat-treated 7075 alloys. Corrosion tests in 3.5% NaCl solution were carried out to assess the corrosion behavior of the as-cast 7075 samples. Results showed significant alterations in microstructural features, including grain refinement and the formation of fine precipitates, attributed to Sc and Li additions, such as MgZn₂, Al₂CuMg, Al₂Cu, Al₃(Sc, Zr), and Al₃Li. These precipitates showed positive effects on the hardness of the present alloys since they are not affected by the formation of precipitate-free zones during the aging processes. However, negative influences of Sc and Li on the corrosion resistance were observed. The corrosion rate was accelerated and reached a value of 0.08 mm/year in the presence of Li + Sc compared to 0.01 mm/year for 7075 base alloy.