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1. Retrogression Forming and Reaging of AA7075-T6 Alclad to Produce Stampings with Peak Strength

   https://doi.org/10.1007/978-3-030-36408-3_35  

   Katherine E. Rader, Jon T. (March 2020, Minerals, Metals and Materials Series: Light Metals 2020)

   A retrogression heat treatment was combined with simultaneous warm forming to produce cross-shaped stampings from AA7075-T6 Alclad sheet. This process is termed retrogression forming. A maximum-allowed- retrogression-forming-time, which includes sheet heat up, transfer, and stamping, was predicted by calculation to achieve peak-aged strength through a single reaging heat treatment after forming. Sheets of 1.6-mm-thick AA7075-T6 Alclad were stamped at 200 °C to a depth of 45 mm within 2 s without splitting. The formed geometry exhibits a complexity appropriate to automotive structural components. These stampings were then subjected to one of two reaging heat treatments. A full reaging heat treatment of 120 °C for 24 h produced strength levels in excess of the original, peak-aged T6 alloy sheet. A sim- ulated paint bake heat treatment at 185 °C for 25 min recovered 95% of the strength lost during warm forming. Successful retrogression forming and reaging of AA7075- T6 provides new possibilities for stamping high-strength aluminum alloys into complex geometries without sacri- ficing strength. 

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2. Review of Retrogression Forming and Reaging for AA7075-T6 Sheet

   https://doi.org/10.1007/978-3-030-65396-5_30  

   Rader, Katherine E.; Carter, Jon T.; Hector, Jr.; Taleff, Eric M. (February 2021, Light Metals 2021, The Minerals, Metals and Materials Series)

   Perander, L. (Ed.)

   Retrogression forming and reaging (RFRA) is a new warm-forming process designed to produce automotive structural components from high-strength aluminum alloys. A scientific approach is described to determine appropriate RFRA conditions for AA7075-T6 and is applied to laboratory-scale forming experiments. The concept of reduced time is used with the activation energy of retrogression measured for AA7075-T6 to predict appropriate times and temperatures for retrogression forming. Conditions recommended for AA7075-T6 are retrogression at 200 °C for 3 to 12 min while forming at strain rates of up to 10^{–1} s^{−1}. The recommended reaging heat treatment to fully restore strength to the T6 condition after retrogression forming is 120 °C for 24 h. These RFRA conditions were successfully applied in laboratory-scale experiments to form AA7075-T6 Alclad sheet and produce a final strength equivalent to the T6 condition. Data from tensile tests provide flow stresses and tensile ductilities across the range of conditions appropriate for RFRA. 

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3. Plastic Flow of AA6013-T6 at Elevated Temperatures and Subsequent Reaging to Regain Full Strength

   https://doi.org/https://doi.org/10.1007/978-3-030-36408-3_56  

   Katherine E. Rader, Jon T. (March 2020, Minerals, Metals and Materials Series: Light Metals 2020)

   Combining a retrogression heat treatment with simulta- neous warm forming can increase the formability of peak-aged, high-strength aluminum alloys while allowing peak-aged strength to be recovered through a single reaging heat treatment after forming. This process is termed retrogression-forming-and-reaging (RFRA). This study investigates the applicability of RFRA to AA6013- T6 sheet material. Elevated-temperature tensile tests were performed at temperatures from 230 to 250 °C and strain rates from 3.2
   10 −3 to 10 −1 s −1 . Tensile tests were followed by reaging with a simulated paint-bake heat treatment. Flow stress at a true strain of 0.10 ranges from 230 MPa (250 °C and 3.2
   10 −3 s −1 ) to 290 MPa (230 °C and 10 −1 s −1 ), significantly lower than the room-temperature yield strength of 360 MPa in the T6 condition. The average elongation to rupture and reduc- tion in area from elevated-temperature tests are 22% and 56%, respectively, which are similar to the room- temperature values for the T4 condition. Elevated- temperature testing reduced material hardness compared to the original T6 condition. Subsequent reaging with a simulated paint-bake raised hardness to 96% of the T6 condition in un-deformed material, but slightly decreased the hardness of the deformed material. Recommendations for implementing RFRA of AA6013-T6 are presented. 

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4. Inter-void shearing effect on damage evolution under plane strain deformation in high-strength aluminum alloy sheet

   https://doi.org/10.1016/j.jmrt.2023.09.079  

   Lee, Jinwoo; Bong, Hyuk Jong; Ha, Jinjin; Kim, Daeyong (September 2023, Journal of Materials Research and Technology)

   In this study, the ductile damage responses of high-strength 7000 series aluminum alloy (AA), AA 7075-T6 sheet samples, subjected to the plane strain deformation mode were investigated using finite element (FE) simulations. In the experiments, uniaxial tension (UT) and plane strain tension (PST) tests were conducted to characterize the plasticity and ductile damage behavior of the AA 7075-T6 sheet samples. The limiting dome height (LDH) and V-die air bending tests were conducted to evaluate the ductility of the material subjected to plastic deformation and friction between the tools, and the corresponding fractured samples were qualitatively analyzed in terms of dimples using fractography. FE simulations were performed to predict the ductility of the AA 7075-T6 sheet samples under plane strain deformation using an enhanced Gurson−Tvergaard−Needleman (GTN) model, namely the GTN-shear model. The model was improved by adding the shear dimple effect to the original GTN model. The predicted results in terms of the load–displacement curves and displacements at the onset of failure were in good agreement with experimental data from the aforementioned tests. Furthermore, virtual roll forming simulations were conducted using the GTN-shear model to determine the effect of the prediction on ductile behavior for industrial applications. 

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5. Numerical Investigation Into the Influence of Alloy Type and Thermo-Mechanics on Void Formation in Friction Stir Welding of Aluminum Alloys

   https://doi.org/10.1115/1.4062270  

   Ansari, Mohammad Ali; Agiwal, Hemant; Franke, Daniel; Zinn, Michael; Pfefferkorn, Frank E.; Rudraraju, Shiva (September 2023, Journal of Manufacturing Science and Engineering)

   Abstract This study employs a high-fidelity numerical framework to determine the plastic material flow patterns and temperature distributions that lead to void formation during friction stir welding (FSW), and to relate the void morphologies to the underlying alloy material properties and process conditions. Three aluminum alloys, viz., 6061-T6, 7075-T6, and 5053-H18, were investigated under varying traverse speeds. The choice of aluminum alloys enables the investigation of a wide range of thermal and mechanical properties. The numerical simulations were validated using experimental observations of void morphologies in these three alloys. Temperatures, plastic strain rates, and material flow patterns are considered. The key results from this study are as follows: (1) the predicted stir zone and void morphology are in good agreement with the experimental observations, (2) the temperature and plastic strain rate maps in the steady-state process conditions show a strong dependency on the alloy type and traverse speeds, (3) the material velocity contours provide a good insight into the material flow in the stir zone for the FSW process conditions that result in voids as well as those that do not result in voids. The numerical model and the ensuing parametric studies presented in this study provide a framework for understanding material flow under different process conditions in aluminum alloys and potentially in other alloys. Furthermore, the utility of the numerical model for making quantitative predictions and investigating different process parameters to reduce void formation is demonstrated. 

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