Tracking microstructural evolution and hardening in Al–Zn–Mg–Cu alloys aged artificially via electrical conductivity measurements

Abstract

Precipitation hardening, a crucial mechanism for strengthening aluminum alloys, involves stages like Guinier–Preston (GP) zone formation, precipitation, peak aging, and precipitate coarsening. This study focuses on the aluminum 7050 alloy, proposing a method to gauge artificial aging through electrical conductivity measurement. The evolving microstructure and time to peak hardness during aging are vital for creating high-strength alloys. The electrical conductivity variation over time is utilized to analyze the diffusion process governing the clustering and growth of specific phases (η′, η, and S) during artificial aging. The paper demonstrates the impact of GP zones, precipitate formation, and grain growth on electrical conductivity, correlating these factors with hardness, microstructure, and tensile strength to determine the hardening stage. Differential electrical conductivity plots, highlighting aging stages, assist in identifying the hardening phase. Tensile strength and hardness plots differentiate the precipitation phases. The Johnson–Mehl–Avrami–Kolmogorov equation models particle growth kinetics, determining growth rates for AA 7050 alloy. The overall activation energy for precipitate growth is 40.77 kJ/mol, with a growth constant ( m) of ∼4, indicating S phase nucleation during η′ and η growth.