An experimental study on microstructure of Friction Stir Welded plates

Friction Stir Welding (FSW) is a solid state welding process for joining
aluminum and other metallic alloys and has been employed in aerospace, rail,
automotive and marine industries. The welding parameters and tool pin profile
play a major role in defining weld quality. The objective of this project is to
compare and characterize the different welded region occurred within the
aluminum alloy when it undergoes the Friction Stir Welding process. The grade
of the aluminum alloy has been identified from the wrought 5xxx series base on
the EDX results which indicates the percentage weight of aluminum of 99.04%
and the remaining are magnesium which comprises of 0.96%. Two plates of
aluminum alloy work piece were set up butted-joint and clamped rigidly to
perform the welding operation. The welded sample was examined using the
optical microscope in order to analyze the development of microstructure across
the welded area. Four different regions can be observed from the welded sample,
which are the nugget zone, thermo mechanically affected zone (TMAZ), heat
affected zone (HAZ) and also the base metal. Relatively the grain shapes were
deformed into fine and small equiaxed grains at the nugget zone to a much
coarser and larger grain size as it heads out towards the base metal. The
development of the grains is due to the dynamic recrystallization phenomena and
also the effect of thermal cycle with respect to the Friction Stir welding process.
Different sets of parameters have been tested on the work piece with varying
rotational speed (rev/min) and also the feed rate (mm/min). Also observed from
the sample was the defect “worm hole”, which might have to do something with
the design of the welding tool.