Method of manufacturing a 7xxx-series aluminium alloy plate product having improved fatigue failure resistance

Abstract

The invention relates to a method of manufacturing an 7xxx-series aluminium alloy plate product having improved fatigue failure resistance, the method comprising the steps of (a) casting an ingot made of an aluminium alloy of the 7xxx-series comprising (in wt. %): Zn 5 to 9, Mg 1 to 3, Cu 0 to 3, balance aluminium and incidental elements and impurities; (b) homogenizing and / or preheating the cast ingot; (c) hot rolling the ingot into a plate product by rolling the ingot with multiple rolling passes, characterized in that when the intermediate thickness of the plate is between 80 and 220 mm, at least a high reduction hot rolling pass is carried out with a thickness reduction of at least 25%, wherein the plate product has a final thickness of less than 75 mm. The invention is also related to an aluminium alloy plate product and an aerospace structural member produced by this method.

Description

FIELD OF THE INVENTION[0001]The invention relates to a method of manufacturing a 7xxx-series aluminium alloy plate product having improved fatigue failure resistance. The plate product can be ideally applied in aerospace structural applications, such as wing skin panels and members, and other high strength end users.BACKGROUND OF THE INVENTION[0002]Al—Zn—Mg—(Cu) type alloys or AA7xxx-series alloys have been used for aircraft constructions for more than 50 years, and particularly for wing members, for example, inter alia, AA7055-series alloys have been used. These aluminium alloys possess a required balance of strength, fracture toughness and corrosion resistance, and are especially well suited for structural aerospace applications such as wing upper skin panels. This is disclosed for example in U.S. Pat. No. 5,221,377. This US patent discloses that in order to obtain these high mechanical characteristics, it is necessary to subject the alloys to a three-stage artificial ageing proce...

AI Technical Summary

Benefits of technology

The invention provides an improved aluminum alloy plate product with better resistance to fatigue failure compared to standard methods. This is achieved by reducing the deformation rate during the high reduction pass of hot rolling, which allows for more intense shearing within the plate material. The plate products can also be cold worked to reduce residual stresses and improve flatness. The manufacturing method produces a plate product with improved properties compared to conventionally processed aluminum alloys.

Problems solved by technology

However, this US patent does not deal with the property of fatigue failure resistance of the AA7055 alloys.

Each type of inspection is very costly, because the aircraft must be taken out of service for the inspection to be performed.

However, keeping the content of impurities Si and Fe at such a very low level increases the costs for the aluminium alloy produced, as materials with a very high purity grade are to be sourced.

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