| 摘要 |
PROBLEM TO BE SOLVED: To produce an aluminum alloy sheet for an aircraft stringer in which the average thickness of crystal grains after a stringer stock is subjected to step cold rolling, preheating treatment and solution treatment is <=40μm even in the part high in a step cold rolling working degree, also aspect ratio is >=4 over the whole length and having excellent stress corrosion cracking resistance of >=250 MPa threshold stress, and to provide a method for producing the same. SOLUTION: This invention is an aluminum alloy sheet having a compsn. contg. 5.1 to 8.4% Zn, 1.8 to 3.0% Mg and 1.2 to 2.6% Cu, moreover contg. one or >= two kinds among <=0.35% Cr, <=0.35% Mn and <=0.25% Zr, and the balance Al with impurities, in which the average thickness of crystal grains is <=25μm, and aspect ratio is >=4. Even in the case the alloy sheet is subjected to cold rolling at partially different working degrees in the range of <=90% working degrees, is subjected to preheating treatment at 350 to 400 deg.C and is thereafter subjected to solution treatment, the average thickness of the crystal grains is <=25μm in the case of <30% working degree and <=40μm in the case of 30 to 90% working degree, and the aspect ratio is maintained to >=4 in both cases.
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