Abstract
A reciprocating extrusion process has been developed for producing hypereutectic Al-20wt.% Si alloys with fine and uniform microstructures and superior properties. Rapidly-solidified layers and cast billets are used as the starting materials. The results show that the interfaces between the layers of the rapidly-solidified alloys could be fully eliminated, and strength and ductility are both improved as the number of extrusion passes increases. For the ingot-processed alloys, the plate-like Si phase in the eutectic and enormous primary Si crystals are refined to a large extent and thus both strength and ductility are increased by 9 and 67%, respectively. Because of having finer Si particles, the rapidly-solidified alloys exhibit a superior combination of mechanical properties to that of the ingot-processed alloys. Fractography demonstrates that the larger Si particles in the ingot-processed material increased the amount of cleavage failure processes.