Real-time ultrasonic measurement during tensile testing of aluminum alloys

A real-time ultrasonic measurement was carried out for aluminum alloy (A2024-T3) specimens during tensile testing with local immersion method by using a water bag to obtain ultrasonic parameters. The sound velocity increased with increasing strain in the elastic deformation, and then decreased with increasing plastic strain during tensile testing. From a relation between the sound velocity and the elastic strain, the acousto-elastic constant was calculated to be 8.5 × 10−6 MPa−1. The surface roughness and the hardness were measured for specimens taken out from testing machine after required strain. The peak intensity of the bottom echo spectrum and the average gradient of the transfer function (AGTF) obtained from the bottom echo spectrum decreased with increasing plastic strain. The decrease in the ultrasonic parameters was explained from the change in the dislocation density and arrangement by using Granato and Lücke string model. The peak frequency of the bottom echo spectrum did not change with increasing plastic strain. The ultrasonic parameters were measured off-line with specimens taken out from testing machine after required strain by the conventional immersion method, and decreased with increasing plastic strain as those obtained in real-time. When specimens were annealed, the hardness continuously decreased with increasing annealing time, and the yield strength and the sound velocity slightly increased after smaller annealing time, and then decreased with increasing annealing time. For annealed specimens, the peak intensity and AGTF obtained by the real-time measurement also decreased with increasing plastic strain, and the rates of the ultrasonic parameters increased with increasing annealing time.