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Abstract

The present invention relates to a method for producing high strength balanced Al—Mg—Si alloy with an improved fatigue crack growth resistance and a low amount of intermetallics, comprising the steps of a) casting an ingot with the following composition (in weight percent) Si: 0.75-1.3, Cu: 0.6-1.1, Mn: 0.2-0.8, Mg: 0.45-0.95, Fe: 0.01-0.3, Zr: <0.25, Cr: <0.25, Zn: <0.35, Ti: <0.25, impurities each less than 0.05 and less than 0.20 in total, balance aluminum, b) optional homogenization of the cast ingot, c) pre-heating the ingot after casting for 4 to 30 hours with temperatures above 520° C., d) hot working the ingot and optionally cold working, e) solution heat treating, and f) quenching the worked product. The pre-heating is preferably performed for 6 to 18 hours with temperatures between 530° C. and 560° C. The alloy has a fatigue crack growth rate at ΔK=20 MPa√m of below 9.0E-04 and at ΔK=40 MPa√m of below 9.0E-03, wherein the amount of intermetallics within the finally worked alloy product, according to the measured specific energy Delta H associated with the DSC signal, is below 1.5 J/g.

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First Claim