Ultrasonic-assisted extrusion of ZK60 Mg alloy micropins at room temperature
A new model of ZK60 magnesium micropins formed through ultrasonic-assisted extrusion at room temperature was developed. The billet was transmitted by the ultrasonic wave during the micropin-forming process. A self-designed apparatus was applied for the ultrasonic-assisted extrusion experiments. The effects of amplitude on the load–displacement curve, load reduction, temperature, microstructure, diameter after extrusion, microhardness, and compressibility of micropins were investigated. The results showed that the punch was always in contact with the billet when the displacement of the punch was larger than the amplitude. The maximum reduction of load was approximately 80% because of the dynamic recrystallization and ultrasonic softening. In addition, load reduction was almost similar under different amplitudes when the diameters of micropins after extrusion were 0.3 and 0.5 mm as a result of the size effect. The microhardness of the micropins increased at the amplitude of 39 and 42 μm as compared with the traditional extrusion. This finding was inconsistent with the results for copper and aluminum. The compression ratio of micropins prepared through ultrasonic-assisted extrusion improved by 14–20% on average at room temperature.