Friction Stir Welding of Ti-6Al-4V Alloy

Abstract:

Titanium (Ti) and its alloys are used extensively in aerospace industry where there is a critical need for material with high strength-to–weight ratio and high elevate temperature properties. Friction stir welding (FSW) is a new solid state welding process in which a cylindrical–shouldered tool with an extended pin is rotated and gradually plunged into the joint between the workpieces to be welded. The material is frictionally heated to a temperature at which it becomes more plastic but no melting of the blanks to be welded is reached therefore the presence of defects typically observed in and close to the welding seam is strongly reduced. The final result is the improvement of the mechanical performances of the welded joints even in some materials with poor fusion weldability. In this paper the authors analyze the microstructure of FSW joints of Ti-6Al-4V processed at the same travel speed (50 mm/min) and at different rotation speed (300-500rpm). The microstructure of base material (BM) is not homogenous. It is characterized by distorted α/ β lamellar microstructure together with smashed zone of fragmented β layer and β retained grain boundary phase. The BM has been welded in the as received state, without any previous heat treatment. The microstructure of the transverse section of joints is not homogeneous. Close to the top of weld cross sections a much finer microstructure than the initial condition has been observed while in the center of the joints the microstructure is mixed and less refined.

• Periodical: Materials Science Forum (Volumes 783-786)
• Pages: 574-579
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.783-786.574
• Online since: May 2014
• Authors: Paola Leo*, Emanuela Cerri
• Keywords: Friction Stir Welding (FSW), Microhardness, Microstructure, Ti6Al4V

References

[1] G. Lutjering, J. C. Williams, Titanium, Springer 2nd edition, New York, (2007).

[2] G. Buffa, L. Fratini, F. Micari, Mechanical and microstructural properties prediction by artificial neural networks in FSW processes of dual phase titanium alloys, Journal of Manufacturing Processes 14 (2012) 289-296.

DOI: 10.1016/j.jmapro.2011.10.007

[3] S.V. Zherebtsov, G.A. Salishchev, R.M. Galeyev, O.R. Valiakhmetov, S. Yu. Mironov, S.L. Semiatin, Production of submicrocrystalline structure in large-scale Ti-6Al-4V billet by warm severe deformation processing, Scripta Materialia 51 (2004).

DOI: 10.1016/j.scriptamat.2004.08.018

[4] Chan Hee Park, Young Gun Ko, Jin-Woo Park, Chong Soo Lee, Enhanced superplasticity utilizing dynamic globularization of Ti-6Al-4V alloy, Materials Science and Engineering A 496 (2008) 150-158.

DOI: 10.1016/j.msea.2008.05.001

[5] S. Zherebtsov, M. Murzinova, G. Salishechev, S.L. Semiatin, Spheroidization of the lamellar microstructure in Ti-6Al-4V alloy during deformation and annealing, Acta Materialia 59 (2011) 4138-4150.

DOI: 10.1016/j.actamat.2011.03.037

[6] S. Mironov, M. Murzinova, S. Zherebtsov, G.A. Salishchev, S.L. Semiatin, Microstructural evolution during warm working of Ti-6Al-4V with a colony-α microstructure, Acta Materialia 57 (2007) 2470-2481.

DOI: 10.1016/j.actamat.2009.02.016

[7] Lijia He, A. Dehghan-Manshadi, R.J. Dippenaar, The evolution of microstructure of Ti-6Al-4V alloy during concurrent hot deformation and phase transformation, Materials Science and Engineering A 549 (2012) 163-167.

DOI: 10.1016/j.msea.2012.04.025

[8] Yu Zhang, Yutaka S. Sato, Hiroyuki Kokawa, Seung Hwan C. Park, Santoshi Hirano, Microstructural characteristics and mechanical properties of Ti-6Al-4V friction stir welds, Materials Science and Engineering A 485 (2008) 448-455.

DOI: 10.1016/j.msea.2007.08.051

[9] L. Zhou, H.J. Liu, P. Liu and Q.W. Liu, The stir zone microstructure and its formation mechanism in Ti6Al4V friction stir welds, Scripta Mater, Vol. 61 (2009), pp.596-599.

DOI: 10.1016/j.scriptamat.2009.05.029

[10] L. Zhou, H.J. Liu, Q.W. Liu Effect of rotation speed on microstructure and mechanical properties of Ti–6Al–4V friction stir welded joints, Materials and Design, Vol. 31 (2010), pp.2631-2636.

DOI: 10.1016/j.matdes.2009.12.014

[11] A. Arora, Z. Zhang, A. De and T Debroy, Strain and strain rates during Friction stir welding, Scripta Materialia61, (2009), 863-866.

DOI: 10.1016/j.scriptamat.2009.07.015