Monitoring gallium-induced damage in aluminum alloys using nonlinear resonant ultrasound spectroscopy

Nonlinear Resonant Ultrasound Spectroscopy is a nonlinear ultrasonic technique which allows monitoring small variations in the microstructure of a medium and thus allows materials characterization and monitoring of damage evolution. Application of the technique to monitor Liquid Metal Embrittlement induced by gallium penetration in aluminum is presented here. To define indicators of material degradation, data treatment using the Singular Value Decomposition approach is introduced and discussed. Experimental results show that nonlinear properties are correlated with the state of the liquid metal in the solid matrix, allowing to identify different phases in the process of gallium diffusion along grain boundaries and within the bulk of individual grains. Furthermore, the evolution of gallium damage allows to study correlations between nonlinear, fast and slow dynamic properties.