Analysis of tool traverse speed in Friction Stir Welding of AZ31 Magnesium alloy thin plates
Abstract
The automotive industry's great interest in lightweight materials, such as
magnesium alloy AZ31, reflects the growing importance of reducing cars' weight.
One of the challenges of using such alloys is that their welding using conventional
fusion methods does not result in good mechanical properties. The low corrosion
resistance typical of these alloys makes it necessary to search for new welding
methods, such as solid-state processes as Friction Stir Welding (FSW). However,
the literature about AZ31 magnesium alloys welded by FSW revealed the
absence of a consensus on the best process parameters for thin plates' welding
as plates used in automotive seats. Therefore, this work aims to analyze the best
combinations of parameters to weld a 2 mm thick AZ31 magnesium plate by FSW
to obtain welds without defects and with good mechanical performance. To meet
this objective, AZ31 plates were welded in two configurations (butt - BW and
overlap – OW), varying only the tool traverse speed, and their mechanical
properties were analyzed by tensile, shear, three-point bending tests, and
microhardness, and the microstructure was observed by optical microscopy.
About the surface finish, the lowest speeds resulted in flashes formation due to
high-temperature development. For BWs, the UTS average increased when the
speed increased until 2 m/min, becoming constant for speeds upper to 2m/min.
For OWs, shear stress values initially increased due to grain refining, however
decreasing with high speeds due to the formation of the large voids. The
hardness profiles were not affected a lot by speed, since its increase resulted in
grain refinement.
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