Method of manufacturing an aluminum alloy sheet for body panel and the alloy sheet manufactured thereby

A method for manufacturing an aluminum alloy sheet for use in a body panel material, comprising the steps of:

• (a) casting a melted aluminum alloy comprising Al, Mg, Fe, Mn, Cr, Ti and Zr, having a Mg content of 4 to 10% by weight, and having contents of Fe, Mn, Cr, Ti and Zr which are determined by a value f satisfying the following equation (I), and the balance of the aluminum alloy being Al,
• 0.4 wt %.ltoreq.f.ltoreq.1.5 wt % (I)
• wherein f=(Fe)+1.1 (Mn)+1.1 (Cr)+3 (Ti)+3 (Zr), wherein (Fe), (Mn), (Cr), (Ti), and (Zr) respectively represent the percentage content by weight of Fe, Mn, Cr, Ti and Zr, to form an ingot, wherein Fe is in an amount of 0.22 to 1.0 wt. %, Mn is in an amount of 1.0 wt. % or less, Cr is in an amount of 0.3 wt. % or less, Ti is in an amount of 0.2 wt. % or less, and Zr is in an amount of 0.3 wt. % or less;
• (b) hot rolling the ingot to obtain a hot rolled sheet;
• (c) cold rolling the hot rolled sheet at a cold reduction percent (R) satisfying the following equation (II), to obtain a cold rolled sheet:
• -log(f-0.2)+8.ltoreq.R.ltoreq.-60 log(f-0.2)+50 (II);
• (d) subjecting the cold rolled sheet to a final annealing treatment including raising the temperature of said rolled sheet to attain a temperature of 450.degree. to 550.degree. C. at a rate of 100.degree. C./minute or more, and maintaining the attained temperature for 300 seconds or less;
• and
• (e) cooling the annealed rolled sheet at a cooling rate of 100.degree. C./minute or more to obtain an aluminum alloy sheet having a grain size of 20 to 80 .mu.m.