The mechanism of the microstructure refinement of metals and alloys (5052 and 6061) by arc oscillating was studied and discussed via the grain size of regular welds and those welded at different oscillation frequencies. In 5052 alloy, fine columnar crystals appeared near the ‘internal fusion line’ during the oscillating arc welding and the grains have been significantly refined by oscillating arc with low and high frequency. However, the grain refinement of 6061 Al alloy was limited during arc oscillating welding due to the different crystal growth pattern at the fusion line and material properties. It is not caused by changing of the grain refinement mechanism but by the difference in the material properties.
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