A RECIPROCATING EXTRUSION PROCESS FOR PRODUCING HYPEREUTECTIC AL-20WT.PERCENT SI WROUGHT ALLOYS

A reciprocating extrusion process has been developed for producing hyp ereutectic Al-20wt.% Si alloys with fine and uniform microstructures a nd 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 eli minated, 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 re fined to a large extent and thus both strength and ductility are incre ased by 9 and 67%, respectively. Because of having finer Si particles, the rapidly-solidified alloys exhibit a superior combination of mecha nical properties to that of the ingot-processed alloys. Fractography d emonstrates that the larger Si particles in the: ingot-processed mater ial increased the amount of cleavage failure processes. (C) 1998 Elsev ier Science S.A. All rights reserved.