Variation of acousto elastic effect in AI6061-T6 according to heat treatment time

The acoustoelastic effect is a phenomenon where the elastic wave velocity varies slightly because of changes in the density or microstructure of the material depending on the variation of tensile or compressive stress. In this paper, we apply the acoustoelastic effect to evaluate the micro-structural changes caused by heat treatment. For this purpose, Al6061-T6 specimens were heat-treated at a constant temperature of 220°C for the seven different heat-treated times. The stress-dependent coefficients were then measured and compared with the variation of the yield strength. The stress-dependent coefficient quantitatively represents the relationship between the variation rate of the ultrasonic wave velocity and applied stress. The ultrasonic wave velocities were measured under the compressive stress state and the time-of-flight(TOF) obtained through the autocorrelation process. The experimental results showed that the heat treatment time at which significant changes in stress-dependent coefficients occurred coincided with the heat treatment time at which a significant change in yield strength occurred. Consequently, it is expected that the variation of yield strength due to heat treatment can be estimated through the acoustoelastic effect