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On the solution treatment of severely deformed AA2024-O and subsequent natural aging

Forouzesh, M ; Sharif University of Technology | 2022

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  1. Type of Document: Article
  2. DOI: 10.1016/j.jmrt.2022.07.090
  3. Publisher: Elsevier Editora Ltda , 2022
  4. Abstract:
  5. In this research, the effect of applying severe strain before solid solution treatment (SST) for AA2024-O was studied. Providing concurrent insights into solutionizing behavior and microstructural evolution corresponding to hardness is important. Multi-directional forging (MDF) was used as a severe plastic deformation (SPD) method. After applying SST on MDFed (4 passes) and as-annealed samples, natural aging (NA) was used as the following treatment to examine the role of severe strain on the solutionizing behavior. In most previous attempts, SPD has been used after SST, but one of the innovations of the present work is the study of SPD before SST. Experimental results show that adding a severe strain using the MDF method before SST results in a significant refinement in the grain size of the solutionized recrystallized microstructure (47 μm). In contrast, coarse-grained microstructures with grain sizes of 150 μm-300 μm are used in prior tries. The results indicate that continuous static recrystallization (CSRX) with a grain size of 47 μm occurs during the solution treatment of the MDFed sample, which is 220% less than that during solution treatment of the as-annealed sample (150 μm); also, rich presence of the second phase particles after its aging by FE-SEM was analyzed. By measuring the difference in hardness before and after NA in solution-treated MDFed and as-annealed samples, 500 °C and 5 min were found to be the most desirable temperature and times in terms of mechanical properties and microstructure. While, in previous efforts, no suitable time has been found for solution treatment of this alloy, and times of 2 h-24 h have been used. The present work found a suitable time of 5 min for solution treatment, which has significant energy savings. In the solution-treated MDFed sample, the maximum hardness of NA (100 HV) was reported; additionally, the percentage of increase in hardness before and after NA (ΔH %) for solution-treated MDFed and as-annealed samples were obtained at 43% and 23%, respectively. Using the DSC test, it was found that in the solution-treated MDFed sample, the peak of S′/S (Al2CuMg) phase formation spreads and shifts from 262 °C to a lower temperature of 235 °C. Using Johnson-Mehl-Avrami (JMA) equations, the values of 103 kJ/mol and 108 kJ/mol were obtained for the activation energy of solution-treated MDFed and as-annealed samples, respectively. Lower activation energy means utilizing Severe Plastic Deformation (SPD) before SST generates a high density of dislocations and vacancies that accelerate solute atoms dissolution and provide S′/S -phase nucleation sites. © 2022 The Author(s)
  6. Keywords:
  7. AA2024 ; Continuous static recrystallization (CSRX) ; Multi-directional forging (MDF) ; Natural aging (NA) ; Solid solution treatment (SST) ; Annealing ; Energy conservation ; Forging ; Grain refinement ; Grain size and shape ; Microstructure ; Oceanography ; Recrystallization (metallurgy) ; Solid solutions ; Aa2024 ; Multi-directional forging ; Natural ageing ; Natural aging ; Solid solution treatment ; Static recrystallization ; Hardness ; Multidirectional forging
  8. Source: Journal of Materials Research and Technology ; Volume 20 , 2022 , Pages 1558-1569 ; 22387854 (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/pii/S2238785422011292