A Study on Peripheral Grain Structure Evolution of an AA7050 Aluminum Alloy with a Laboratory-Scale Extrusion Setup
- 105 Downloads
A laboratory-scale hot extrusion setup was designed to investigate recrystallization and grain growth behavior of an AA7050 alloy during extrusion and subsequent heat treatments. Compared with industrial extrusion, the laboratory-scale process enabled rapid water quenching of extrudate with less delay so that the dynamic grain structure development was captured. After extrusion, static microstructure evolution in the extrudates was studied using salt bath annealing for 5 and 15 s at 490 °C and solutionization treatment for 1 h at 490 °C. The salt bath annealing was a simulation of the delay of press quenching in typical industrial extrusion practices. In the as-quenched extrudates, the peripheral region mainly exhibited continuous dynamic recrystallization and geometric dynamic recrystallization, whereas in the core region discontinuous dynamic recrystallization dominated. A <100> and <111> double fiber texture was identified in extrudates, and recrystallization behavior was found to be orientation dependent. The <100> oriented grains contained more sub-grain boundaries and better-defined sub-grains and had a higher tendency to fragment via continuous recrystallization, while the <111> oriented grains produced less sub-grain boundaries and did not recrystallize. Subsequent heat treatments resulted in static recrystallization and abnormal growth of the continuously recrystallized grains. Additionally, the effects of extrusion temperature (440, 480 and 520 °C) and punch speed (0.7, 1.4 and 2.1 mm/s) on grain structure were discussed. A revised grain structure evolution mechanism based on the observation of 7050 extrusion was proposed.
Keywords7050 alloy extrusion grain growth recrystallization
The authors gratefully acknowledge financial support on this research from Shandong Nanshan Aluminum Co. and Beijing Nanshan Institute of Aeronautical Materials. Materials for the project donated by Arconic Lafayette Operations are also acknowledged.
- 20.T. Sheppard, Chapter 3: Metallurgical Features Affecting the Extrusion of Aluminum Alloys, in: Extrusion of Aluminum Alloys (Springer , Berlin, 2013), pp. 81–86Google Scholar
- 22.T. Furu, R. Østhus, N. Telioui, R. Aagård, M. Bru, O.R. Myhr, Modeling the Effect of Mn on Extrudability, Mechanical Properties and Grain Structure of AA6082 Alloys, in Eleventh International Aluminum Extrusion Technology Seminar & Exposition (2016), pp. 567–590.Google Scholar
- 23.F.J. Humphreys, M. Hatherly, Chapter 9: Recrystallization of Two-Phase Alloys, in Recrystallization and Related Annealing Phenomena, (Elsevier, 2012), pp. 311-314Google Scholar
- 25.F.J. Humphreys, M. Hatherly, Chapter 3: Deformation Textures, in Recrystallization and Related Annealing Phenomena (Elsevier, 2012), pp. 78–79Google Scholar
- 32.M. Bauser, K. Siegert (eds.), Chapter 5: The Production of Extruded Semi-Finished Products from Metallic Materials, in Extrusion, (ASM International, 2006), p. 232Google Scholar
- 33.O. Reiso, Extrusion of AlMgSi Alloys, Mater. Forum, 2004, 28, p 32–46Google Scholar
- 34.F.J. Humphreys, M. Hatherly, Chapter 7: Recrystallization of Single-Phase Alloys, in Recrystallization and Related Annealing Phenomena, (Elsevier, 2012), pp. 228–229Google Scholar