Hot extrusion of AA 7178 reinforced with alumina short fibre

Abstract

Hot extrusion of an AA 7178 based composite reinforced with alumina short fibres (FRM) was examined in the temperature range between 723 K (a solid state) and 773 K (a semisolid state). Although alumina fibres became well aligned along the extrusion direction for the entire temperature range, a higher extrusion temperature made the FRM stronger by suppressing the chopping of fibres during extrusion. The longitudinal tensile strength at 573 K was improved by 70% compared with the AA 7178 alloy with no reinforcement. Semisolid state extrusion, resulted in tears on the surface of the rod. To suppress tearing, a clad extrusion method involving an AA 6061 surface layer was developed. By this method, semisolid extrusion could be performed without tearing.MST/737