Microstructural Interactions during Stress Ageing a 7475 Aerospace Alloy

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.

Evolution of precipitate microstructure during stress aging of an Al–Zn–Mg–Cu alloy

“…9. Microstructure of the stress-free aged sample was represented coarser precipitate size distribution than that of the stress-aged specimens, which is in agreement with the observations of Bakavos [26]. Very densely distributed fine Șƍ precipitates, which contribute more to the hardness [34], were formed in the alloy after 25 (Fig.…”

“…On the other hand, Skrotzki et al [25] explored the stress aging process of Al-Cu-Mg-Ag alloy and found that the external stress results in changes in the size and morphology of the GP zones, șƍ and ȍ precipitates. Bakavos [26] and Lin [27] paid attention to the stress aging treatment of Al-Zn-Mg-Cu alloys recently and the results revealed that significant interactions take place during the aging stages.…”

“…Unfortunately its application is limited to the small-section aluminum alloys due to the very short retrogression time. Some researches [22][23][24][25][26][27] in the last 30 years suggest that the precipitation could be modified dramatically during aging under elastic stress (namely, stress aging). To analyze this precipitate evolution during stress aging might be helpful to improve the compromise between the mechanical strength and the corrosion resistance: In 1975, Hosford [23] firstly observed that the stress has noticeable influence on the habit of șƍ precipitate platelets in Al-Cu alloy.…”

Effects of pre-treatments on aging precipitates and corrosion resistance of a creep-aged Al–Zn–Mg–Cu alloy

“…Furthermore, the GP II zones are preferably oriented on {1 1 1} planes lying $35°to the tensile stress axis. However, this effect rapidly disappears when the GP zones transform to g 0 phases during the second stage creep-aging treatment [30]. Lin et al [31] investigated the effects of creep-aging temperature and external stress on the precipitation process of 7075 aluminum alloy, and found that the creep-aging processing can refine the precipitates.…”

Evolution of Precipitate Microstructure During Creep of an AA7449 T7651 Aluminum Alloy

“…The microstructure evolution during creep forming has received sparse attention in the literature. [9][10][11][12][13] In 7000 series aluminum alloy, Li et al [14] very recently showed some accelerated precipitate growth and coarsening that led to a reduction of mechanical properties. However, a quantitative analysis of the evolution of precipitates as a function of temperature and applied creep stress is not available yet.…”