| 摘要 |
A method of superplastic extrusion is provided for fabricating large, complex-shaped, high strength metal alloy components, such as large, thin cross section, closed-box panels or integrally "T-stiffened" aircraft skin panels. Superplastic extrusion is similar to conventional extrusion except that strain rate and temperature are carefully controlled to keep an ultra-fine grain high strength metal alloy within the superplastic regime where deformation occurs through grain boundary sliding. A high strength, heat treatable metal alloy is first processed, such as by equal channel angular extrusion (ECAE), to have a uniform, equiaxed, ultra-fine grain size in thick section billet form. Temperature and strain rate are controlled during superplastic extrusion of the ultra-fine grained billet so that the stresses required for metal flow are much lower than those needed in conventional extrusion. The low stresses allow use of more fragile extrusion dies, including multi-hale dies for hollow core extrusions, thereby achieving thinner section details in larger extruded components for a given press loading capacity. After superplastic extrusion, components may be solution treated, stretch straightened, and creep-age formed in an autoclave, as required. The resulting large, compound curvature, thin section, integrally stiffened, high strength metal alloy components retain a uniform, equiaxed, fine grain size, which imparts superior strength, isotropy, ductility, toughness, and corrosion resistance compared with conventional grain sized metal alloys.
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