Original Article

Effects of prolonged retrogression and re-aging (RRA) heat treatment on the corrosion and electrochemical behavior of AA7075 alloy

¹ Computational and Experimental Materials Innovation Group (CEMIG), Department of Metallurgical Engineering, NED University of Engineering and Technology, 75270, Pakistan
² Department of Industrial and Manufacturing Engineering, NED University of Engineering and Technology, 75270, Pakistan
³ Department of Mechanical Engineering, NED University of Engineering and Technology, 75270, Pakistan

^* Corresponding author: m.siddiqui@cloud.neduet.edu.pk

Received: 22 March 2025
Accepted: 30 September 2025

Abstract

Aluminum alloy AA7075 is prized for its high strength-to-weight ratio, but its corrosion resistance under prolonged exposure remains a critical concern. This study investigates the effects of extended retrogression and re-aging (RRA) heat treatment on the corrosion and electrochemical behavior of AA7075 alloy. The alloy underwent retrogression at 180 °C, 240 °C, and 320 °C for 12 h, followed by re-aging at 100 °C for 10 h. Corrosion performance was evaluated in a 3.5% NaCl solution, analyzing corrosion current density, corrosion potential, corrosion rate, charge transfer resistance, and double-layer capacitance. Results revealed that retrogression temperature significantly influenced corrosion resistance. The alloy treated at 240 °C exhibited optimal performance, with a corrosion current density of 3.1 μA/cm², charge transfer resistance of 2697 Ω cm², and double-layer capacitance of 1.42 μF/cm². XRD analysis identified beneficial precipitates, including MgZn₂, Al₂CuMg, and Al₅₀Mg₄₈Cu, along with optimized dislocation density (12.47 lines/nm²), crystallite size (28.63 nm), and microstrain (0.9). These factors contributed to enhanced corrosion resistance by influencing precipitate nucleation and growth. The findings highlight the importance of precise RRA heat treatment parameters in tailoring the alloy’s microstructure for improved corrosion resistance, offering valuable insights for engineering applications in corrosive environments. This study provides a foundation for optimizing AA7075 alloy performance in real-world scenarios.