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1
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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.
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2
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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.
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