Influence of Zirconium Addition on Heat Treatment Response, Microstructure, and Corrosion Resistance of AA7075 Alloy for Aerospace Applications

The AA7075 alloy is widely used in the aerospace industry, particularly for its high strength-to-weight ratio in the production of critical structural components such as wing spars, fuselage frames, landing gear supports, rocket booster casings, and high-stress fasteners. This study was designed to enhance the strength and service performance of the AA7075 alloy. In this study, AA7075 alloy was mechanically alloyed with different amounts of Zr (0, 0.075, 0.15, and 0.30 wt.%), followed by cold pressing and sintering in a controlled atmosphere furnace. The AA7075 + Zr alloys produced were subjected to retrogression and re-aging (RRA) heat treatment. The microstructural characteristics of the RRA-treated AA7075 + Zr alloys were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mechanical properties were evaluated through density, microhardness, and corrosion tests. Consequently, the influence of different Zr additions on the RRA heat treatment response of AA7075 alloy produced by (MA) Mechanical alloying was investigated. Microstructural examinations, including SEM imaging and EDS analysis, revealed that Al was the predominant element, while variations in elemental composition were observed in certain regions. According to the XRD results, Al, Al2CuMg, Al2Cu, and MgZn2 phases were identified. With the addition of Zr, Al3Zr, Al3Zr4, and Al3Zr5 phases were formed. The lowest surface roughness (Ra) value of 0.078 µm was obtained for the AA7075 + 0.30 wt.% Zr alloy. The corrosion tests conducted in a 3.5% NaCl solution demonstrated a progressive improvement in the corrosion resistance of the AA7075 alloy as the Zr content increased. The corrosion rate was 1.9 mm/year for the AA7075 alloy, decreasing to 0.19 mm/year for the AA7075 + 0.30 wt.% Zr alloy. SEM examination of the corroded surfaces revealed localized surface degradation characterized by the formation of corrosion pits, indicating a predominantly pitting corrosion mechanism.