The effect of ultrasonic vibrations prior to high pressure die-casting of AA7075

The effects of introducing ultrasonic vibrations prior to high pressure die casting have been experimentally investigated. Results suggest reductions of up to 73% in grain size and up to 5% on porosity levels due to cavitation, leading to enhanced structural performance. The typical values of ultimate tensile stress and yield stress increased respectively to 590 MPa and 502 MPa and elongation improved to 18%. Wetting of the oxides by the collapse of cavitation bubbles along with enhanced degassing appears to be the responsible mechanisms for these property improvements. The effect of relaxation time after ultrasonic vibrations examined and results indicate slight grain size increase from 68 to 80 mu m. Proving ultrasonic treatment above liquidus appears to be a stable phenomenon where its effects remaining active for a considerable time, making the process feasible for industrial scale applications. (C) 2015 Elsevier B.V. All rights reserved.