Characterisation of the Deformation Microstructure in Friction StirWelded 7075 T6 Aluminium Alloy using the SEM-EBSD Technique

摘要

In the present investigation the deformation microstructures forming during friction stirrnwelding (FSW) of 7075 T6 aluminium alloy have been examined. This has been done byrnmeans of the electron back-scattered diffraction (EBSD) technique in a scanning electronrnmicroscope (SEM). In the as-welded condition a dynamically recrystallised microstructure isrnrevealed in the weld region consisting of very fine 1-2 μm equiaxed grains mainly separatedrnby high angle grain boundaries. The resulting pole figures show evidence of sharp textures inrnthe microstructure. However, different texture components are observed in different regionsrnof the weld nugget.rnAfter high temperature annealing at 500℃ for 60 minutes this microstructure becomesrnunstable and is replaced by coarse irregular grains with different texture components. Thernobserved phenomenon bears a close resemblance to secondary recrystallisation (or abnormalrngrain growth), which is characterised by the rapid growth of a few grains in a recrystallisedrnmicrostructure that already is stabilised by second phase particles (here dispersoids) in thernparent material.