Synchrotron X-ray strain scanning has been used to determine the residual s
tress distribution over the cross-sectional area of a friction stir weld ac
ross an I-section made of extruded aluminium alloy type AA 7108 in the T79
condition. Measurements were made using the 311 reflection and a wavelength
of about 0.35 Angstrom. The dominant longitudinal residual stress field is
tensile within and to just outside the friction band where the field drops
steeply. Further out there are regions of balancing compression falling to
near zero at the outer edges of the sample. The longitudinal residual stre
sses vary within the range from -60 to 140 MPa. The transverse residual str
esses are generally weaker but show a more marked through-thickness variati
on below the friction band. The residual stress maps show detailed features
which are related to the heat flow from crown to root faces and difference
s between the advancing and retreating sides. The results demonstrate that
synchrotron strain scanning is a practicable technique for determining non-
destructively internal and through-surface residual strains in light elemen
t components. The synchrotron technique complements and extends the range a
t present covered by neutron and X-ray diffraction methods and is capable o
f substantial development.