METHOD OF PRODUCING HIGH STRENGTH BALANCED AL-MG-SI ALLOY AND A WELDABLE PRODUCT OF THAT ALLOY

摘要

The present invention relates to a method of 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, V: <0.25, Hf: <0.25, impurities each less than 0.05 and less than 0.20 in total, balance aluminium; b) optional homogenisation of the cast ingot; c) pre-heating the ingot after casting for 4 to 30 hours at temperatures above 520 °C; d) hot working the ingot and optionally cold working; e) solution heat treating; and f) quenching the worked product. Said 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 DeltaK=20 MPa√m of below 9.0E-04 and at DeltaK=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.