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Fatigue behaviour of notched specimens of friction stir
welded aluminium alloy 6063-T6
P.M.G.P. Moreira ∗ , F.M.F. de Oliveira, P.M.S.T. de Castro
ˆ
˜
Departamento de Engenharia Mecanica e Gestao Industrial, Faculdade de Engenhariada Universidade do Porto, 4200-465 Porto, Portugal

article

info

abstract

Article history:

Notwithstanding the widespread interest in the possibilities offered by friction stir welding

Received 30 October 2007

(FSW), data concerning its mechanical behaviour is still needed. Due to design constraints,

Received in revised form

friction stir welded components may includenotches in the weldment (friction stirred mate-

8 December 2007

rial), and there is a lack of information on the fatigue behaviour of the weldment in those

Accepted 22 December 2007

conditions. In this work the influence of FSW on the fatigue life of specimens of aluminium
alloy 6063-T6, containing notches in the thermo-mechanically affected zone was studied.
For this purpose, welded andunwelded notched specimens were fatigue tested under load

Keywords:

control at different stress levels. Compared to base material specimens, FSW specimens

Fatigue life

were found to have longer fatigue lives but generally of the same order of magnitude. The

Friction stir welding

work included hardness, tensile and fatigue tests, and the finite element method analysisMicrostructures

of the stress and strain distribution. Microstructure examination and microhardness mea-

Scanning electron microscopy

surements were performed, and in order to identify welding defects and fracture surface

Strain-based approach of fatigue life

features a scanning electron microscopy analysis was carried out. The notch-strain analysis
was used for approximate modelling of thefatigue behaviour observed.
© 2008 Elsevier B.V. All rights reserved.

1.

Introduction

Friction stir welding (FSW), a solid-state welding process
developed and patented by the TWI in 1991, emerged as a
welding technique to be used in high-strength alloys that
were difficult to join with conventional technique (Thomas et
al., 1995). The process was developed initially for aluminiumalloys, but since then FSW was found suitable for joining a
large number of materials. In aeronautics, for instance, riveting is the preferred manufacturing process for aircraft fuselage
structures; nevertheless, FSW is emerging as an appropriate
alternative technology due to low distortion, high strength of
the joint and high-processing speeds. In the FSW process a
non-consumable rotating tool,consisting of a shoulder and
profiled probe or pin, is forced down into the joint line under
conditions where the frictional heating is sufficient to raise

∗

Corresponding author. Tel.: +351 22508 3450; fax: +351 22508 1584.
E-mail address: pmgpm@fe.up.pt (P.M.G.P. Moreira).
0924-0136/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmatprotec.2007.12.113the temperature of the material to the range where it is plastically deformed (Negre et al., 2003). In the recent years research
has been carried out in several types of friction stir welded
joints. Leal and Loureiro (2004) studied the effect of the weld
travel speed on the defect formation, on the changes in the
microstructures and on the mechanical properties of welds in
aluminium alloys. Itwas verified that friction stir welded joint
defects are mainly cracks or voids and are originated by large
plastic deformation and hardening of the material. Steuwer
et al. (2006) quantified the effect of tool traverse and rotation
speeds on the residual stresses for welds between a non-agehardening and age-hardening one. It was found that the region
around the weld line was characterised...