Experimental investigation on ultrasonic-assisted extrusion of aluminum fabricated by ultrasonic powder consolidation

Abstract

Ultrasonic powder consolation (UPC) is a rapid, low-temperature powder consolidation process which is viable for the commercial production of high-density bulk materials, particularly with the use of secondary forming to create net-shape products. To this end, the acoustic softening effect may provide an effective means for secondary forming. In this study, gas-atomized aluminum powders were employed to produce UPC samples as the raw materials for the subsequent ultrasonic-assisted extrusion experiments. Three process parameters, temperature, pressure and ultrasonic vibration time, were selected to systematically investigate the influence of ultrasonic vibration on the formability of the UPC samples. Measurement of extrusion length showed that the extrusion of UPC samples is promoted by higher pressure and temperature. The effective strain rate varied with the ultrasonic vibration time. At lower temperature, the strain rate increased initially and then decreased, while it decreased at first and then increased at higher temperature. Image analysis of the microstructure of the extruded UPC samples showed that the extruded samples were partitioned into five distinct regions exhibiting different microstructures. The shear zone expanded as ultrasonic vibration applied, and the orientation of the powder particles slightly deflected after 4 s of ultrasonic irradiation, which corresponded to the reduction in strain rate. The hardness of each region increased with time, except for the extruded zone where no additional deformation took place. Parallel extrusion experiments with commercial-grade 1100 aluminum, supplied as rod, have shown that UPC aluminum samples have higher deformability in ultrasonic-assisted extrusion.