Papers by Keyword: AA7475

Abstract: 2XXX and 7XXX high strength aluminum alloys are the most used materials for structural parts of aircrafts due to their high strength/weight ratio. Their joining procedure is an engineering challenge since they present low weldability. Friction Stir Welding (FSW) is a joining technology developed in the early 90 ́s. It is a solid-state welding process, without the use of fillers or gas shield, that eliminates conventional welding defects and has been considered of great interest for application in the aircraft industry. FSW of aluminum alloys results in four regions of different microstructures, specifically: the base material (BM), the heat affected zone (HAZ), the thermo-mechanically affected zone (TMAZ), and the nugget zone (NZ). The complex microstructure of the weld region leads to higher susceptibility to localized corrosion as compared to the BM even when similar alloys are joined. The welding of dissimilar alloys in its turn results in even more complex microstructures as materials with intrinsically different composition, microstructures and electrochemical properties are put in close contact. Despite the great interest in FSW, up to now, only few corrosion studies have been carried out for characterization of the corrosion resistance of dissimilar Al alloys welded by FSW. The aim of this study is to investigate the corrosion behavior of aluminum alloy 2024-T3 (AA2024-T3) welded to aluminum alloy 7475-T761 (AA7475-T761) by FSW. The evaluation was performed in 0.01 mol.L^-1 by means of open circuit potential measurements, polarization techniques and surface observation after corrosion tests.

Abstract: After superplastic deformation of Al-7475 and some other aluminium alloys, straininduced cavities are seen to be associated with long fibres parallel to the tensile direction. These fibres, whiskers or filaments are also observed on the fracture surface. This effect has become known as microsuperplasticity. The whisker characteristics are affected by the deformation conditions, particularly temperature and strain rate. To study the effect of these variables more fully, tensile samples of Al 7475 have been strained to failure at temperatures ranging from 480OC to 530OC and strain rates from 1.0E- 04s-1 to 5.0E-03s-1. Additional samples were deformed at 450OC and 420OC and a single strain rate. Some whiskering was observed under all testing conditions. The longest whiskers were generally seen at high temperatures and low strain rates. A TEM study of macroscopic whiskers produced under conditions of around 540OC and 1.0E-04 /s showed an amorphous structure. Annealing prior to deformation was shown to have little effect on whisker formation. EDX analysis showed the whole surface of the alloy to be enriched in alloying elements compared with the bulk alloy. The high levels of Mg detected were connected with the formation of magnesia as the surface oxide verified using Cr3+ fluorescence microscopy. Use of the differential scanning calorimeter (DSC) showed no conclusive evidence of partial melting below the testing temperatures. Considerations of capillarity and the DSC analysis suggest whiskering did not occur by a mechanism of viscous flow.

Abstract: In creep-ageforming a material experiences continuously variable bending stresses through its thickness, from tensile to compressive, which are maximum at the surfaces. This can potentially result in through thickness microstructural gradients, due to interactions between the bending stresses, creep, and precipitation occurring during ageing, that can alter a component’s performance. The aim of the work reported here was to develop an understanding of these effects in an industrial creep ageforming process. For this purpose two aerospace alloys, 7475 and 2022, were ageformed by Airbus UK using industrial scale ageforming tools. Their microstructures were analysed in detail by TEM, and SAXS, which revealed significant through thickness microstructural changes after forming.

Abstract: In industrial process, like creep-ageforming, materials are aged under load. To investigate the influence of an applied stress on the ageing behaviour of Cu bearing Al-7xxx series alloys, a 7475 alloy was aged under a constant tensile stress and analysed by means of Small Angle X-ray Scattering (SAXS) and TEM. Mechanical testing was also employed, to determine if there was any effect on the materials strength. The results show that during the early stages of ageing significant interactions takes place, which preferentially aligns one type of GP zone, as well as affecting their size and volume fraction. During the second stage ageing treatment, the applied stress was observed to cause more rapid over-ageing, by promoting the formation of the η phase.