Functional Gradation in Precipitation Hardenable AA7075 Alloy by Differential Cooling Strategies

Abstract:

Inspired by steel forming strategies, this study focuses on the effect of differential cooling on mechanical properties and precipitation kinetics during hot stamping of high strength AA7075 alloy. For this aim, different forming strategies were performed using segmented and differentially heated forming tools to provide locally tailored microstructures. Upon processing, uniaxial tensile tests and hardness measurements were used to characterize the mechanical properties after the aging treatment. Microstructure investigations were conducted to examine the strengthening mechanisms using the electron channeling contrast imaging (ECCI) technique in a scanning electron microscope (SEM). Based on the obtained results, it can be deduced that the tool temperatures play a key role in influencing the mechanical properties. Lower tool temperatures result in higher material strength and higher tool temperatures in lower mechanical properties. By changing the cooling rate with the use of differently heated forming tools, the mechanical properties can be controlled. Microstructure investigations revealed the formation of very fine and homogeneously distributed particles at cooled zones, which were associated with elevated mechanical properties due to the suppression of second phase particle formation during cooling. In contrast, coarse particles were observed at lower cooling rates, explaining the lower material strength found in these zones.

• Periodical: Key Engineering Materials (Volume 883)
• Pages: 159-166
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.883.159
• Online since: April 2021
• Authors: Emad Scharifi*, Moritz Roscher, Steffen Lotz, Ursula Weidig, Eric Jägle, Kurt Steinhoff
• Keywords: Aluminium, Differential Cooling, Hot Stamping

References

[1] Y. Liu, L. Wang, B. Zhu, Y. Wang, Y. Zhang, Identification of two aluminum alloys and springback behaviors in cold bending, Procedia Manufacturing. 15 (2018) 701–708.

DOI: 10.1016/j.promfg.2018.07.303

[2] X.G. Wang, Q.S. Li, R.R. Wu, X.Y. Zhang, L. Ma, A Review on Superplastic Formation Behavior of Al Alloys, Advances in Materials Science and Engineering. 2018 (2018).

[3] J. Lin, D. Trevor A., G. Richard P., F. Alistair D., Process for forming metal alloy sheet components, 2008. https://patents.google.com/patent/WO2008059242A2/en.

[4] D.H. Ko, J.H. Kim, C.J. Lee, D.C. Ko, B.M. Kim, Evaluation of formability and mechanical characteristic for hot forming quenching in sheet forming of A16061 Alloy, Transactions of the Korean Society of Mechanical Engineers, A. 37 (2013) 483–490.

DOI: 10.3795/ksme-a.2013.37.4.483

[5] P.F. Bariani, S. Bruschi, A. Ghiotti, F. Michieletto, Hot stamping of AA5083 aluminium alloy sheets, CIRP Annals - Manufacturing Technology. 62 (2013) 251–254.

DOI: 10.1016/j.cirp.2013.03.050

[6] H. Gao, T. Weng, J. Liu, C. Li, Z. Li, L. Wang, Hot stamping of an Al-Li alloy: A feasibility study, MATEC Web of Conferences. 21 (2015) 0–4.

DOI: 10.1051/matecconf/20152105007

[7] X. Fan, Z. He, K. Zheng, S. Yuan, Strengthening behavior of Al-Cu-Mg alloy sheet in hot forming-quenching integrated process with cold-hot dies, Materials and Design. 83 (2015) 557–565.

DOI: 10.1016/j.matdes.2015.06.058

[8] S.J. Yuan, X.B. Fan, Z. Bin He, Hot forming-quenching integrated process with cold-hot dies for 2A12 aluminum alloy sheet, in: Procedia Engineering, Elsevier Ltd, 2014: p.1780–1785.

DOI: 10.1016/j.proeng.2014.10.232

[9] S. V. Sajadifar, E. Scharifi, U. Weidig, K. Steinhoff, T. Niendorf, Effect of Tool Temperature on Mechanical Properties and Microstructure of Thermo-Mechanically Processed AA6082 and AA7075 Aluminum Alloys, HTM Journal of Heat Treatment and Materials. 75 (2020) 177–191.

DOI: 10.3139/105.110412

[10] K. Steinhoff, N. Saba, M. Maikranz-Valentin, U. Weidig, Optimized processes and products in hot sheet metal forming, in: Steinhoff, K.; Oldenburg, M.; Prakash, B. (Edtrs.): Proceedings of the 2nd International Conference on Hot Sheet Metal Forming of High-Performance Steel, Auerbach (D), 2009: p.29–42.

DOI: 10.1002/srin.200806322

[11] M. Merklein, M. Wieland, M. Lechner, S. Bruschi, A. Ghiotti, Hot stamping of boron steel sheets with tailored properties: A review, Journal of Materials Processing Technology. 228 (2016) 11–24.

DOI: 10.1016/j.jmatprotec.2015.09.023

[12] E. Scharifi, S.V. Sajadifar, G. Moeini, U. Weidig, S. Böhm, T. Niendorf, K. Steinhoff, Dynamic Tensile Deformation of High Strength Aluminum Alloys Processed Following Novel Thermo‐Mechanical Treatment Strategies, Advanced Engineering Materials. (2020) 2000193.

DOI: 10.1002/adem.202000193

[13] H. Zhao, F. De Geuser, A. Kwiatkowski da Silva, A. Szczepaniak, B. Gault, D. Ponge, D. Raabe, Segregation assisted grain boundary precipitation in a model Al-Zn-Mg-Cu alloy, Acta Materialia. 156 (2018) 318–329.

DOI: 10.1016/j.actamat.2018.07.003

[14] E.A. Jägle, Z. Sheng, L. Wu, L. Lu, J. Risse, A. Weisheit, D. Raabe, Precipitation Reactions in Age-Hardenable Alloys During Laser Additive Manufacturing, Jom. 68 (2016) 943–949.

DOI: 10.1007/s11837-015-1764-2