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
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