Patent ID: 7727346

Claim:
Method of producing a wrought aluminium alloy rolled product comprising the steps of: (i) providing an intermediate alloy product, having a composition (in wt. %) consisting of: Mg 4.05 to 4.31 Mn 0.5 to 0.6 Zn 0.4 to 0.6 Cu 0.085 to 0.18 Cr 0.11 to 0.2 Fe<0.2 Si<0.12 Zr<0.01 Ti at most 0.02 impurities each ≦0.05, total of max. 0.15, and balance aluminium; (ii) homogenization annealing a slab of the alloy; hot rolling the homogenization annealed slab to form an intermediate alloy product; cold working the intermediate alloy product by cold rolling to a final gauge of 0.7 to 4 mm to obtain an intermediate wrought product; and (iii) continuously annealing the intermediate wrought product by heating the product at a heating rate in the range of 80 to 200° C./sec, holding the product at a soaking temperature in the range of 520 to 550° C. for a duration of at most 40 sec, followed by a cooling rate in the range of 10 to 500° C./sec to below a temperature of 150° C. to arrive at plates in H111-temper; wherein the product after annealing has a weight loss after sensitising for 100 hours at 100° C. of less than 15 mg/cm 2 when tested against intergranular corrosion in accordance with ASTM G67.