Attempts have been registered scientifically mostly for strained hardened Al alloys towards improvement of formability at warm temperatures. The varieties of possible precipitate populations add complexity in determining the mechanisms of work-hardening behaviour of the precipitation hardened alloys. Efforts were made, in the current work, to investigate the work-hardening response for EN AW-6016 and EN AW-6061 sheets of different temper (T4 and T6) at room and warm temperatures (150 and 250 °C) and at two different strain rates (0.1 and 0.01 s⁻¹) through tensile experiments. Among these variants, the influence of temperature has been detected the most on yield strength and work-hardening rate. Lowering the efficiency of storing dislocations as well as activating dynamic recovery, both are responsible for the reduction in work hardening rate proportionally with temperature. The work-hardening model originally developed by Prof. E. Nes (Nes model) has been chosen to simulate the experimental stress-strain response of both alloys at room and warm temperature as the phenomenology of the model promised a better constitutive description of work hardening. Because Nes model was primarily designed for strained hardened Al alloys, the bottleneck, to apply this model for precipitation hardened alloys, was removed by adding contribution from the precipitates in terms of mean slip length of dislocations in the current version. The validity of the model was examined for 130 °C, 150 °C and 180 °C and at a strain rate of 0.1s⁻¹, once satisfied fitting was achieved for 6016 and 6061 alloys at RT and 250 °C at a strain rate of 0.01s⁻¹. The decrease of dynamic recovery during the change of temper state (T4 to T6) during RT deformation can be explained as a competition between solute depletion and precipitate growth. With minute quantitative differences, the influence of strain rate and temperature was reproduced well by the model.

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AA7050 is an aluminum alloy with superior mechanical properties; however, it is prone to hot tearing (HT) during its production via direct-chill casting. This study focuses on extracting constitutive parameters of the alloy thermomechanical behavior in semi-solid state as well as gaining insight in its failure behavior. Tensile tests were performed using an Instron 5944 at solid fractions between 0.85 (550 °C) and 1.0 (465 °C), at deformation rates of 0.2 and 2 mm/min. The results showed that there are three mechanical behavior regimes in this solid fraction range: ductile at 1.0 (T = 465 °C) ≤ f_s < 0.97 (T = 473 °C), brittle at 0.97 (T = 473 °C) ≤ f_s ≤ 0.9 (T = 485 °C) and then ductile again (at 0.9 (T = 485 °C) < f_s ≤ 0.85 (T = 550 °C)). Fracture surface analysis revealed that the fracture mode was mostly intergranular with fracture propagating through solid bridges as well. Semi-solid constitutive parameters were obtained by making a simple thermal model and numerical tensile tests in ALSIM software package and comparing the simulation results with experimental mechanical tests. The extracted constitutive parameters and available information from the literature support the fact that AA7050 is more susceptible to HT than AA5182 and Al-2 wt pct Cu alloys. The obtained parameters can further enhance the predictive capability of computer simulations of direct-chill casting.

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No recrystallization of austenite, Tnr, has an important influence on the transformed phase -fractions and the final crystallographic texture after hot deformation. This paper investigates the evolution of microstructure and texture components during hot-rolling in two austenitic region based on Tnr along with three different cooling trajectory and coiling in dual-phase steels and high strength low alloys steel. The recrystallization of the austenite, the austenite deformation followed by the austenite-to-ferrite transformation influence the final microstructure and texture in dual phase steels, have been examined by means of optical microscopy, X-ray diffraction (XRD) measurements. Recrystallized and deformed austenite have clearly different texture components and, due to the specific lattice correspondence relations between the parent austenite phase and its transformation products, the resulting ferrite textures are different as well.@en

Formability had been important property of metals which is attributed to the texture development during thermomechanical processing particularly during hot rolling and cold rolling. In the present paper, the high strength steels with different carbon and manganese composition have been hot rolled above and below of austenite recrystallization temperature and followed by fast cooling up to different coiling temperature to get hot bands with different texture and two phase microstructure consisting ferrite with pearlite, bainite and martensite. Subsequently, these hot bands were cold rolled with 80 percent under plain strain condition. The microstructure of cold rolled sheets samples were analyzed using scanning electron microscope and showed the cold rolled microstructure with strong pancaked of two phase which was carried from the hot rolling. Cold rolled texture in ferrite pearlite microstructure is completely replaced by new texture components from hot rolled condition without the effect of Tnr. Hot rolled texture was retained in ferrite-bainite and martensite microstructure with the effect of Tnr. Increase in alloy chemistry weakens the texture intensity in ferrite pearlite/bainite microstructure. Whereas increase in alloy chemistry strengthens the texture intensity in ferrite martensite microstructure. @en

The knowledge on constitutive mechanical behavior at the temperatures close to the solidus is essential for predicting high-temperature deformation and fracture, e.g. cold and hot cracking of aluminum alloys. In this work we studied the tensile mechanical properties of an as-cast AA7050 alloy in a near-solidus temperature regime. Tensile tests were carried out using Gleeble-3800™ system at temperatures from 400 to 465 °C and at strain rates from 0.0005 to 0.05 s⁻¹. The results show that the strength decreases with increasing temperature and decreasing strain rate. Meanwhile, ductility decreases with the increase of temperature and strain rate. The constitutive parameters were extracted by fitting the test data to the extended-Ludwik and creep-law equations. The parameters for the extended-Ludwik equation are continuous with the values from a lower temperature regime obtained earlier, while the parameters for the creep-law equation are comparable with those obtained on other 7XXX aluminum alloys. We observed a change in fracture mode at 450 °C; from ductile transgranular to intergranular. This temperature coincides with the discontinuity point of the temperature-ductility slope. On the fracture surface of a sample that was deformed at 465 °C with a strain rate of 0.0005 s⁻¹, we observed features characteristic of micro-superplasticity. Considering the test conditions, viscous flows of incipient melt or liquid-like substances are suggested to be responsible for the formation of this feature.

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issn 1757-8981@en