Analysis of Particle-Stimulated Nucleation (PSN)-Dominated Recrystallization for Hot-Rolled 7050 Aluminum Alloy
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HIGH-STRENGTH, precipitation-hardening, 7xxx aluminum alloys such as AA7050 are widely used in the aviation industry because they consolidate highstrength, low-density, better stress-corrosion cracking resistance, and stronger fracture toughness.[1–3] AA7050 is one of the best choices for thick part applications such as wing ribs, spars, and fuselage frames.[4] The critical applications of these alloys will necessitate further investigation and development in various areas associated with the thermal processing. The mechanical properties of these alloys are affected by evolved structure (grain size and texture) during recrystallization.[5] Recrystallization reduces strength and toughness and can decrease the corrosion resistance of aged alloys. A small volume fraction of recrystallization is tolerable for structural applications requiring high strength.[6,7] Modeling the microstructural evolution during recrystallization can aid in optimizing the recrystallized fraction for applications and industrial needs. The production of 7050 aluminum alloys goes through a series of processing stages including casting, homogenization, preheating, hot rolling, solutionizing, quenching, and aging.[1,5] Decomposition and KHALED F. ADAM and DAVID P. FIELD are with the School of Mechanical and Materials Engineering, Washington State University, PO Box 642920, Pullman, WA, 99164. Contact e-mail: [email protected] ZHENGDONG LONG is with Kaiser Aluminum, 15000 E Euclid Ave, Spokane Valley, WA 99216. Manuscript submitted August 25, 2016. Article published online January 20, 2017 2062—VOLUME 48A, APRIL 2017
precipitation of second-phase particles can take place during any of the processing stages, which in turn influences the evolving structure of the following stages.[1,5] The spatial distribution of these particles depends on the cooling rate, prior microstructure, and local chemistry composition.[1] S-phases (Al2CuMg), M-phase, or g-phase MgðZn2 ; AlCuÞ2 and T-phase are the most common precipitated phases in 7050 Al alloy, in addition to the insoluble iron and silicon-rich constituent particles that form during ingot solidification.[1,4,8] These particles persist through hot rolling and are hard enough to hamper the metal flow during the hot-rolling process.[4] The stored deformation energy in these regions is high, and high misorientation gradients develop in the vicinity of such particles.[4,9–11] Unlike much of the published work, the distribution of nucleation sites used as input for the simulations was determined from real experiments obtained from the BSE micrographs.[12] Anisotropy of the subgrain boundary energy was implemented into the Monte Carlo code.[13,14] Nevertheless, adding the Zirconium to add control over the recrystallized grain structure in 7050 aluminum alloys is important. The metastable coherent Al3Zr dispersoids greatly hinder the recrystallization process.[4–8,15–18] Particles of Al3Zr pin grain and subgrain boundaries make grain growth more challenging in areas far from the large particle. These Al3Zr disper
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