Patent ID: 6565684
Filing Date: 2003-05-20
Classification: C22C,C22F

Abstract:
A process for manufacturing a hollow pressure vessel, comprising the steps of:a) casting a billet from an aluminum alloy with a composition consisting essentially of, in % by weight, Zn=6.25-8.0, Mg=1.2-2.2, Cu=1.7-2.8, Fe<0.20, Fe+Si<0.40, at least one of the elements selected from the group consisting of Cr, Zr, V, Hf, Sc in an amount of 0.05-0.3, and other elements <0.05 each and <0.15 total, remainder Al; b) homogenizing the billet with a temperature profile such that metal temperature is slightly less than incipient melting temperature at all times; c) returning the homogenized billet to ambient temperature, then softening annealing the homogenized billet for a duration of 20 to 40 h between 200 and 400Â° C., followed by cooling at a rate of less than 50Â° C./h down to a temperature of below 100Â° C., resulting in a billet hardness <54 HB; d) cutting a slug out of the softened billet; e) cold or slightly warm extrusion of the slug, with an extrusion start temperature <300Â° C., to form a casing; f) necking the casing; g) solution heat treating the casing at a temperature slightly below the incipient melting temperature, for a duration sufficient to obtain an absolute value of specific energy associated with a DTA thermogram signal of less than 3 J/g; h) quenching the solution heat treated casing in cold water; and i) aging the quenched casing at between 100 and 200Â° C. for a duration between 5 and 25 h.