Dissolution and Precipitation Behavior for Hot Forming of 7021 and 7075 Aluminum Alloys

Milkereit, Benjamin; Österreich, Martin; Schuster, Philipp A.; Kirov, Georg; Mukeli, Ermal; Keßler, Olaf

doi:10.3390/met8070531

Cited by 33 publications

(29 citation statements)

References 27 publications

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“…In Ref. [161], we showed that the heat-flow development during isothermal soaking in a differential scanning calorimeter at the solution treatment temperature can be used to estimate the duration of the dissolution processes. Based on this, suitable solution treatment parameters can be derived.…”

Section: Achieving a Complete Solid Solutionmentioning

confidence: 99%

“…For the 7xxx alloys with highest concentration of alloying elements such as 7075, 7049A ( Figure A3 in the Appendix A and Refs. [161,162]) and 7068 [192], cooling DSC appears to show only one very broad peak, which ranges from about 450 to 150 • C. It can be assumed that this very broad heat effect is caused by the sum of numerous reactions. The in situ cooling DSC experiments shown in Figure 49 cover four orders of magnitude and thereby an extreme dynamic DSC.…”

Section: XXX Alznmg(cu) Wrought Alloysmentioning

confidence: 99%

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Review of the Quench Sensitivity of Aluminium Alloys: Analysis of the Kinetics and Nature of Quench-Induced Precipitation

et al. 2019

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For aluminium alloys, precipitation strengthening is controlled by age-hardening heat treatments, including solution treatment, quenching, and ageing. In terms of technological applications, quenching is considered a critical step, because detrimental quench-induced precipitation must be avoided to exploit the full age-hardening potential of the alloy. The alloy therefore needs to be quenched faster than a critical cooling rate, but slow enough to avoid undesired distortion and residual stresses. These contrary requirements for quenching can only be aligned based on detailed knowledge of the kinetics of quench-induced precipitation. Until the beginning of the 21st century, the kinetics of relevant solid-solid phase transformations in aluminium alloys could only be estimated by ex-situ testing of different properties. Over the past ten years, significant progress has been achieved in this field of materials science, enabled by the development of highly sensitive differential scanning calorimetry (DSC) techniques. This review presents a comprehensive report on the solid-solid phase transformation kinetics in Al alloys covering precipitation and dissolution reactions during heating from different initial states, dissolution during solution annealing and to a vast extent quench-induced precipitation during continuous cooling over a dynamic cooling rate range of ten orders of magnitude. The kinetic analyses are complemented by sophisticated micro- and nano-structural analyses and continuous cooling precipitation (CCP) diagrams are derived. The measurement of enthalpies released by quench-induced precipitation as a function of the cooling rate also enables predictions of the quench sensitivities of Al alloys using physically-based models. Various alloys are compared, and general aspects of quench-induced precipitation in Al alloys are derived.

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Section: Achieving a Complete Solid Solutionmentioning

confidence: 99%

Section: XXX Alznmg(cu) Wrought Alloysmentioning

confidence: 99%

Review of the Quench Sensitivity of Aluminium Alloys: Analysis of the Kinetics and Nature of Quench-Induced Precipitation

et al. 2019

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“…For hot stamping, rapid cooling from solution heat treatment temperature to room temperature is necessary during stamping for optimal artificial ageing potential. We have shown earlier that our setup fulfils this requirement [6]. In W-temper forming, the sheets are formed in the W state directly after quenching from solution heat treatment temperature.…”

Section: Introductionmentioning

confidence: 75%

“…Figure 2 shows the temperature-time and forming sequences of the process chains investigated. For all process chains, the sheets were solution heat treated according to the annealing parameters identified by Milkereit et al [6]: 515 • C/5 min for 7021; 480 • C/15 min for 7075. For hot stamping (HS, Figure 2a), the sheets were transferred as fast as possible from solution heat treatment to the press (within approximately 25 s).…”

Section: Materials and Process Chainsmentioning

confidence: 99%

Characterisation and Comparison of Process Chains for Producing Automotive Structural Parts from 7xxx Aluminium Sheets

Schuster

Österreicher

Kirov

et al. 2019

Metals

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Due to their high specific strength, EN AW-7xxx aluminium alloys are promising materials for reducing the weight of automotive structural parts. However, their formability at room temperature is poor due to pronounced natural ageing. Therefore, we investigated hot stamping and W-temper forming for EN AW-7075 and a modified variant of EN AW-7021. For hot stamping of the modified EN AW-7021, a low-temperature stabilisation heat treatment (pre-aging at 80 °C for 1 h) was incorporated into the process chain design to inhibit natural ageing after forming. The process chains were compared with respect to dimensional accuracy, mechanical properties, microstructure, precipitation status (assessed by differential scanning calorimetry) and crashworthiness. It was found that hot stamping is suitable to form failure-free parts with good dimensional accuracy for both alloys while W-temper forming suffers from springback. Within a time-span of 21 days after forming, hardness values of hot stamped and stabilised parts did not increase significantly. Compared to non-stabilised parts, stabilised parts also showed significantly improved folding behaviour in quasi-static compression testing and absorbed approximately 15% more energy.

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“…As the relevant precipitation reactions frequently overlap, DSC often does not allow the separation of single reactions or the ability to evaluate their specific precipitation enthalpies [14]. Sometimes, particularly for high concentration alloys, the overlapping of single reactions is so severe that DSC detects just one broad peak [15].…”

Section: Introductionmentioning

confidence: 99%

In-situ analysis of continuous cooling precipitation in Al alloys by wide-angle X-ray scattering

Rowolt

Fröck

Reich

et al. 2020

Science and Technology of Advanced Materials

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The aim of this work is to investigate quench induced precipitation during continuous cooling in aluminium wrought alloys EN AW-7150 and EN AW-6082 using in situ synchrotron wideangle X-ray scattering (WAXS). While X-ray diffraction is usually an ex situ method, a variety of diffraction patterns were recorded during the cooling process, allowing in situ analysis of the precipitation process. The high beam energy of about 100 keV allows the beam to penetrate a bulk sample with a 4 mm diameter in a quenching dilatometer. Additionally, the high intensity of a synchrotron source enables sufficiently high time resolution for fast in situ cooling experiments. Reaction peaks could be detected and compared with results from differential scanning calorimetry (DSC) by this method. A methodology is presented in this paper to evaluate WAXS data in a way that is directly comparable to DSC-experiments. The results show a high correlation between both techniques, DSC and WAXS, and can significantly improve continuous cooling precipitation diagrams.

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Dissolution and Precipitation Behavior for Hot Forming of 7021 and 7075 Aluminum Alloys

Cited by 33 publications

References 27 publications

Review of the Quench Sensitivity of Aluminium Alloys: Analysis of the Kinetics and Nature of Quench-Induced Precipitation

Review of the Quench Sensitivity of Aluminium Alloys: Analysis of the Kinetics and Nature of Quench-Induced Precipitation

Characterisation and Comparison of Process Chains for Producing Automotive Structural Parts from 7xxx Aluminium Sheets

In-situ analysis of continuous cooling precipitation in Al alloys by wide-angle X-ray scattering

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