Reaging Heat Research Articles

Effect of Ag content and heat treatment on the stress corrosion cracking of Al–4.6Cu–0.3Mg alloy

A201 aluminum alloy, Al–4.6Cu–0.3Mg–0.6Ag, is a high-strength as-cast alloy which is strengthened by Ω-phase and θ′-phase. The Ω-phase is a thermal stable strengthening phase, and the θ′-phase is known as the strengthening phase of the binary Al–Cu alloy. The amount of Ag in the alloy and the heat treatment affect the precipitation of the Ω- and θ′-phases as well as the morphology of the phases that precipitate at the grain boundary, affecting the susceptibility of the alloy to stress corrosion cracking. In this study, the susceptibility of various Ag-containing Al–4.6Cu–0.3Mg alloys stress corrosion cracking in a 3.5% NaCl solution was investigated for alloys tempered to T6 and T7 conditions, the retrogression and re-aging heat treatment also applied. The microstructure of the alloys was elucidated by optical microscopy and transmission electron microscopy, and susceptibility to stress corrosion cracking was assessed by performing the slow strain rate test in air and salt solution. The findings indicated that the continuous grain boundary precipitations and the high Ag concentration alloy that exist high density of the Ω- and θ′-phases caused susceptibility to high stress corrosion cracking. The presence of a wide precipitation-free zone and discontinuous large particles in the grain boundary precipitates caused the T7 alloy to have a low susceptibility to stress corrosion cracking. The alloys tempered to the RRA condition cannot reduce susceptibility of the Al–Cu–Mg–Ag alloy to stress corrosion cracking.

Influence of overaging on the mechanical properties and stress corrosion cracking behaviour of 7075 T6 aluminium alloy

The effect of a reageing heat treatment following a T6 temper on the mechanical properties and the stress corrosion cracking behaviour (SCC) on the EN AW 7075 aluminium alloy is studied. The reageing time was 27 hours for all the temperatures used: 147, 152 and 163 °C; this last temperature is indicated in the MIL-H-6088F standard to obtain the T73 temper from the T6 temper. The mechanical properties and the stress corrosion behaviour are evaluated and, compared with the T6 and T73 tempers. The evolution of the microstructure is analysed with transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) techniques, and related with the properties. The reageing following to the T6 temper made a more stable structure higher the temperature, and, consequently, lowing the stress corrosion susceptibility. For temperatures lower than 147 °C, this diminution of stress corrosion susceptibilityoccurs without reducing the mechanical properties. So, the 147 °C reageing heat treatment has better stress corrosion behaviour than the T6 temper, with similar mechanical properties. By the other hand, the stress corrosion susceptibility achieved with the 152 °C reageing is slightly worse than the T73 one, but their mechanical properties are better.

Influence of retrogression and reaging on microstructure, mechanical properties and susceptibility to stress corrosion cracking of an Al‐Zn‐Mg alloy

AbstractThe aim of the present work was to determine the influence of the retrogression and reaging (RRA) heat treatment on the correlation between microstructure, mechanical properties and susceptibility to stress corrosion cracking (SCC) of the AlZn5Mg1 alloy in dry air and sea water. The alloy received in the T6 temper was subjected to 9 different heat treatments, including retrogression at temperature 453–513 K for 600–3600 s, and reaging at temperature 363 K or 403 K for 16 h, 24 h or 48 h. The susceptibility to SCC was investigated by slow strain rate tensile tests at 10−6 s−1 strain rate; change in time to failure, fracture energy and reduction in area were taken into account. Generally, the heat treatment improving mechanical properties increased susceptibility to SCC. The observed effects were discussed in terms of change in microstructure, especially size and distribution of phase precipitates. The role of change in dislocation network was the most likely of no importance.

Influence of retrogression and reaging on fracture toughness of 7010 aluminium alloy

Compact tension fracture toughness specimens of high strength aluminium alloy 7010 have been tested after the application of retrogression and reaging (RRA) heat treatments. Short transverse orientation specimens, 25 mm in thickness were cut from a large rectilinear open die forging. Two retrogression temperatures were investigated, 200 and 240 ° C, and the RRA treatments were applied to material in the solution treated and cold compressed (W52) condition. Varying the retrogression time and temperature strongly influences the fracture toughness and does so to a degree that is greater than would be expected from the change in tensile properties alone. The fracture toughness, tensile properties and work hardening characteristics of alloy 7010 are reported and their dependence on retrogression time and temperature is described.

Improvements in Strength and Stress Corrosion Cracking Properties in Aluminum Alloy 7075 via Low-Temperature Retrogression and Re-Aging Heat Treatments

Abstract The susceptibility of aluminum alloy 7075 (AA7075 [UNS A97075]) to intergranular stress corrosion cracking (SCC) in the peak strength T6 temper is alleviated through the use of the T73, or over-aged temper, which provides improved SCC resistance with a 10% to 15% strength loss compared to the T6 temper. Previous research has indicated that retrogression and re-aging (RRA) heat treatments reduce the trade-off between T6 strength and T73 SCC resistance. The short-term heat treatment they used, however, limited the applicability of RRA to thin sections of material. The primary goals of this research effort were to determine if lower retrogression temperatures could be used in the RRA process to extend the applicability of this heat treatment to thick section aircraft components and to quantify any observed improvements. Alternate immersion (AI) and double-cantilever beam (DCB) tests were conducted in a 0.6-M sodium chloride (NaCl) solution to evaluate the SCC resistance of various tempers. Improveme...

Retrogression and Reaging of 7075 T6 Aluminum Alloy

The objective of this study was to investigate the feasibility of performing retrogression and reaging (RRA) heat treatments on 7075-T6 aluminum alloy in muffle furnaces instead of salt and oil baths. The retrogression temperatures were 180°C, 200°C, 220°C and 240°C. and retrogression times were 5, 10, 15 and 25 minutes. Reaging was performed at 120°C for 24, 36 and 48 hours. Tensile testing, hardness and electrical resistivity measurements were determined.

Differential scanning calorimetry evaluation of retrogressed and re-aged microstructures in aluminum alloy 7075

Differential scanning calorimetry (DSC) experiments were performed to evaluate the effects of retrogression and re-aging heat treatments on the precipitate microstructures of aluminum alloy 7075 in the T651 temper condition. The retrogression heat treatments varied from 15 to 240 s at temperatures between 220 and 270°C; the re-aging treatment was 24 h at 120°C. DSC analyses showed that both retrogression treatments and retrogression and re-aging treatments caused significant changes in the precipitate microstructures. It was found that the retrogression treatments caused precipitate dissolution and overaging and that the progress of this treatment could be accurately evaluated by DSC analysis. The final microstructure was found to be highly dependent on the retrogression treatment, and the final microstructure was both unique and significantly different from the T651 and T73 conditions.