Abstract
Static flow stress decreases abruptly when ultrasonic oscillatory stress (17.8 kHz) is intermittently superimposed. The decrement in static flow stress, Δσ was measured in an Al-5 at%Mg alloy. The ranges of strain rate and testing temperature were from 1×10−4 to 1×10−3 s−1 and from 473 to 673 K, respectively. Δσ was zero at 673 K. This implies that dislocation velocity at 673 K is proportional to effective stress. Δσ at 473 and 573 K was dependent on oscillatory stress amplitudes, strain rates and testing temperatures. These experimental results indicate that the dislocation velocity-effective stress exponent, m* is greater than unity at lower temperatures. The change in m* with temperature and strain rate is satisfactorily explained in terms of a solute-dislocation interaction.
