Toughness-strength relations in the overaged 7449 al-based alloy

Abstract

This article examines the relationship between plane strain fracture toughness, K Ic , the tensile properties, and the microstructure of the overaged 7449 aluminum-plate alloy, and compares them to the 7150 alloy. The 7449 alloy has a higher content of Ј/ precipitates; and, the 7150 alloy contains a greater amount of coarse intermetallic particles, as it contains an appreciable amount of coarse S phase (Al 2 CuMg), which is largely absent in the 7449 alloy. The toughness of the alloys shows an increase on overaging, and the 7449 alloy shows a reasonably linear toughness-yield strength relation on extended overaging. Several mechanisms of failure occur: coarse voiding at intermetallics and a combined intergranular/transgranular shear fracture mode, with the former becoming more important as overaging progresses. Drawbacks of existing models for toughness are discussed, and a new model for plane strain fracture toughness, based on the microstructurally dependent work-hardening factor, K A , introduced in Ashby's theory of work hardening, is developed. This model predicts a linear relation between K Ic and K 0.85ys , where ys is the yield strength, which is consistent with the experimental data.

A model for the electrical conductivity of peak-aged and overaged Al-Zn-Mg-Cu alloys

“…Between about 290 and 470°C all curves are dominated by an endothermic effect due to η dissolution. Whilst underaged 7xxx alloys show a strong exothermic peak due to η′ and η formation between about 200 and 270°C [51], the DSC curves of the present peak aged and overaged alloys only show a remnant of this effect between about 220 and 290°C, in the form of a relatively small exothermic effect superimposed on a dominant endothermic effect. Thus the DSC curves in Fig.…”

Predicting grain refinement by cold severe plastic deformation in alloys using volume averaged dislocation generation

“…This strength increase proportional to square root of strain (a parabolic stress strain curve) has been observed in a range of plastically non-homogeneous materials including polycrystalline materials [21]. This proportionality is only valid over a limited strain range, which is alloy dependent and has been estimated to be between about 0.01 to 0.05 [21,55].…”

“…The increase in K A due to non shearable particles was given as [21]: where C 2 is a constant equalling about 0.25 [21]. From measured K A values (determined in this work and from the literature [55,56]) in Table 2 it can be seen that Mg considerably increases K A . In the alloys concerned Mg is dissolved in the FCC Al phase.…”

“…To this end we first obtain K A experimentally from stress-strain curves for plastic strains 0.01 to 0.05. (It is noted K A may also be estimated from measured work hardening exponents using a conversion described in [55]). …”

Relations between microstructure, precipitation, age-formability and damage tolerance of Al–Cu–Mg–Li (Mn, Zr, Sc) alloys for age forming

“…The composition of alloy 6 is close to the median composition of 2024. Compositions of alloys 3-4 and 7-10 are aimed to achieve a yield strength that does not significantly exceed 2024-T351 yield strength as increasing yield strength is detrimental to toughness in aluminium alloys [11], whilst a high yield strength is also thought to reduce age formability, especially if the strength is caused by solution strengthening. The addition of Li in selected alloys was made to take advantage of the associated improved fatigue crack growth resistance but Li contents were limited to 1.6 wt% to limit formation of δ' (Al 3 Li) precipitates which are associated with reduced toughness.…”