Effect of Electromagnetic Stirring on Weld Solidification Structure of Aluminum Alloys (Report I) : Investigation on GTA Weld Metal of Thin Sheet

概要

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In order to make clear the mechanism of grain refinement of weld metal structure by means of stirring of molten metal, GTA bead-on-plate welding without filler metal was performed for thin sheet of aluminum alloy using an electromagnetic stirring process. Then, the effect of the intensity and the frequency of magnetic field, welding speed and welding current on weld solidification structure were investigated. Moreover the contributions of the magnetic stirring to extinction of the porosity and the feathery crystal and to homogeneity of composition were investigated. Main conclusions obtained are as follows ; (1) Alternate magnetic field is effective on grain refinement. There is the optimum frequency for grain refinement and the optimum frequency is nealy proportional to welding speed. (2) The strong magnetic field is effective to grain refinement, but there is an upper limit owing to formation of a burnt-through bead. (3) The grain refinement is remarkable in the welding condition where the welding speed is low and the whole weld metal is almost composed of columnar crystals. Therefore, at a high welding speed where equiaxed crystal zone is formed in the weld center, the effect of the magnetic field is little. (4) The magnetic stirring is effective to eliminate the formation of feathery crystal and porosities. (5) The magnetic stirring is effective to homoginize the composition of the weld metal.
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