The effects of ultrasonic treatments on the microstructure and mechanical properties of SAC0307 solder

The microstructures and physical properties of SAC0307 lead-free solder formed by an ultrasound-assisted semisolid casting process were analyzed. The damages to a thin aluminium foil placed in the alloy melt at 226 degrees C showed strong effects of acoustic streaming. Significant erosion due to cavitation was found for powers higher than 450 W. Numerical simulations of a collapsing cavitation bubble obtained the highest peak pressure and temperature when the ultrasonic power was around 550 W. When the ultrasonic power was between 500 W and 600 W, sub-grains were observed and the crystal grains became equiaxed with the smallest average grain size of about 140 mu m. The highest tensile strength found in this range was about 36.6 MPa. The density was 7.35 g/cm(3). The elongation at break was about 60%, which was 40% higher than the value obtained by traditional casting techniques.