Comparative study of linear and nonlinear ultrasound applied to the detection of hydrogen damage in 7N01 aluminum alloy

Abstract 7N01 aluminum alloy samples with different hydrogen damage degrees were prepared by electrochemical hydrogen charging technology. 7N01 aluminum alloy samples with different degrees of hydrogen damage were characterized by metallographic observation, hardness test and XRD test. The results show that the hydrogen content increases with the increase of hydrogen charging time. The surface of aluminum alloy is exfoliated and pits appear. The more severe the hydrogen damage, the greater the depth of pits. The microhardness of the 7N01 aluminum alloy decreases after hydrogen damage, which only occurs near the surface. After electrochemical hydrogen charging, AlH 3 appears in the structure of 7N01 aluminum alloy, which is the result of increased hydrogen concentration. The ultrasonic echo signals of hydrogen damaged samples were obtained by a high frequency longitudinal probe ultrasonic detection device, and the results of linear and nonlinear ultrasonic detection were compared. Traditional linear ultrasonic detection parameters such as sound velocity and attenuation coefficient do not change significantly in the early stage of hydrogen damage, but increase significantly in the late stage of hydrogen damage. Due to the change of microstructure, the nonlinear coefficient increases approximately linearly in the early stage of hydrogen damage and decreases in the late stage of hydrogen damage. This study demonstrates the potential for combining linear and nonlinear ultrasonic measurements in hydrogen environment to more comprehensively study hydrogen damage.