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Precipitates are the primary source of strength for the Al-Mg-Si alloy. Aluminum alloy in the peak-aged state mainly contains β" and β' precipitates. Most of the literature has only considered the strengthening effect of β". Here, we develop a single-crystal intensity model including both precipitate enhancement effects for the first time. This model was subsequently implemented into a crystal plastic finite-element method to model the uniaxial tensile process of a polycrystalline aggregate model of Al-Mg-Si alloy. The simulation results for uniaxial stretching are in good agreement with the experimental results, confirming that the constitutive parameters used for the single-crystal strength model with two precipitates are based on realistic physical implications. Furthermore, by comparing the uniaxial tensile simulation results of a peak-aged alloy considering the actual precipitated phase composition of the alloy with those assuming that the precipitated phase is only the β" phase, the predicted tensile strength of the former is around 5.65% lower than that of the latter, suggesting that the two kinds of precipitation should be separately considered when simulating the mechanical response of Al-Mg-Si alloy. It is highly expected that the present simulation strategy is not limited to Al-Mg-Si alloys, and it can be equally applied to the other age-enhanced alloys. [ABSTRACT FROM AUTHOR]

Good stress relaxation stability enables heat-resistant aluminum alloys to serve well at high temperatures. From the viewpoint of simultaneous regulation of microstructure and precipitates, a deliberate pre-annealing (200–400 ℃) followed by solution-aging (T6) treatment was proposed to improve the stress relaxation stability of an Al-Cu-Mg-Ag heat-resistant aluminum alloy in this work. A peak effect on the stress relaxation stability was found with a pre-annealing temperature of 325 ℃, which is associated with larger-sized grains and finer-sized precipitates of the alloy. This interesting peak phenomenon is attributed to a good balance of recrystallization and precipitation. Moreover, the regulated microstructure surprisingly assisted the 325 ℃ pre-annealing+T6 treated alloy with good tensile properties. The proposed heat treatment method provides a route for developing high-performance heat-resistant aluminum alloys. [Display omitted] • A heat-resistance Al alloy was prepared via pre-annealing/solution-aging treatment. • Regulation of grains and precipitates improved stress relaxation stability. • The alloy showed higher tensile properties than the alloy without pre-annealing. [ABSTRACT FROM AUTHOR]

Clarifying the aging characteristics of aluminum alloys during continuous heating is crucial for formulating isothermal and non-isothermal aging (continuous heating aging) processes. This paper investigates the stress relaxation characteristics of an Al-Cu-Mg-Ag alloy under three-point bending during continuous heating. Taking into account the mechanical properties and precipitate analysis, it demonstrates the feasibility of using the stress relaxation method to determine the peak aging temperature during continuous heating. This approach is efficient, requires minimal sample, and yields continuous data. The peak aging temperature of the sample increases from 260 °C to 305 °C when the heating rate increases from 1 to 3 °C/min with the same initial load (3 N). The peak aging temperature is around 280 ℃, when the initial load increases from 1 N to 9 N with the same heating rate (2 °C/min). Under low temperatures (25 ℃∼ 200 ℃), the sample displays the presence of GP zones, and a few Ω precipitates during the continuous heating process of 2 ℃/min. As the temperature increases, the GP zones dissolve and transform into the Ω precipitates. A large number of Ω precipitates appear in the matrix in a continuous precipitation manner when the temperature reaches 235 °C. The precipitation strengthening effect is strongest at 280 °C, and the Ω precipitates begin to coarsen as the temperature exceeds 280 °C. [Display omitted] • A method to determine the continuous heating peak aging temperature of aluminum alloys was proposed. • The peak aging temperature of Al-Cu-Mg-Ag alloy was related to the heating rate. • The evolution of the precipitates during continuous heating aging of Al-Cu-Mg-Ag alloy was obtained. [ABSTRACT FROM AUTHOR]

In heat-resistant Al–Cu–Mg–Ag alloys, the presence of AgMg segregation layer on Ω phase ensures its high thermal stability. It was reported Ω precipitation would be inhibited when Si was added such that the Mg/Si mass ratio was lower than 2. However, in this work, it has been proved the notable increase in Ag content from 0.5% to 0.8% could still promote precipitation of Ω besides θ′ in an Al–Cu–Mg–Ag–Si alloy with a Mg/Si mass ratio around 1.7. The key point is to obtain an Ag/Mg excess atomic ratio greater than 1 under the premise of W(Mg)/W(Si) > 1.4 in the supersaturated solid solution, where Mg excess denotes the remaining Mg solutes after the formation of C/L phase. Although the fine precipitation of Ω in the 0.8 Ag alloy increases the total volume fraction of precipitates and yield strength, their quick coarsening at high temperature leads to a more pronounced strength loss. Such a comparison reveals the fully enveloped Ω precipitate is less stable than the θ′ precipitate with multiple interface phases. These findings update our knowledge on the systematic composition design for tunning Ω/θ′ precipitates' ratio and properties of Al–Cu–Mg–Ag–Si alloys. [ABSTRACT FROM AUTHOR]