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Abstract
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The 7020-T6 aluminum alloy plates of 4 mm thickness
were friction stir welded at rotational speeds of 400, 600,
800, and 1000 rpm and constant traverse speed of 100 mm/
min. The peak temperatures of the joints were recorded by
precise thermocouples. Microstructure, hardness, tensile properties,
and fracture surfaces of the joints were analyzed. The
results showed that decreasing the tool rotational speed from
1000 to 400 rpm decreased the peak temperature from 311 to
209 °C, and hence caused a lower heat input. In addition,
lower rotational speeds result in higher hardness and tensile
strengths. The higher hardness and ultimate tensile strength
were related to the grain boundary, precipitation, and substructure
strengthening mechanisms. In addition, the fracture surfaces
of the joints welded at higher heat input conditions
showed more ductile mode in comparison with that of welded
at lower heat input condition, which confirmed the lower tensile
elongation of the joints welded at lower rotational speeds.
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