Appeal 2007-2359
Application 90/006,951
19. The Specification teaches that Mn is not generally useful for
improving the toughness of alloys of the present invention. (359 patent
at 3:17-20.)
20. To avoid increased levels of dispersoid formation upon quenching,
Mn levels are kept below 0.15%, preferably below 0.10%. (359 patent
at 3:20-23.)
21. Cu is said to improve tensile strength without a comparable increase
in extrusion breakthrough pressure, but to increase corrosion problems.
(359 patent at 3:53–58.)
22. The Specification discloses that Si in excess of the amount required to
combine with all the Mg as Mg2Si and with all the Fe and Mn as
Al(Fe,Mn)Si (a nonstoichiometric formula) is desirable to achieve the
desired tensile strength; but that too much excess Si adversely affects the
extrusion surface quality and "formability" of the alloy. (359 patent
at 3:59-4:11.)
23. According to the Specification, as-cast extrusion ingots are
homogenized to bring the soluble secondary magnesium-silicon phases into
suitable form, to dissolve the silicon, and partly to convert β-AlFeSi
particles into substantially α-AlFeSi particles. (359 patent at 4:19-24.)
24. Homogenization is accomplished by heating the ingot to a
temperature higher than 530°C for 30 minutes to 24 hours, depending on the
temperature. (359 patent at 4:24-26.)
25. Following homogenization, the ingot is cooled to a
temperature ≤ 425°C, preferably at a rate of at least 150°C per hour.
(359 patent at 4:27–32.)
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