Frank Eberl

Microstructural interactions during stress ageing a 7475 aerospace alloy

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.

Through Thickness Microstructural Gradients in 7475 and 2022 Creep - Ageformed Bend Coupons

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.