Microsegregation in Aluminum Weld Metal and Electron Microscopic Observation of Weld Solidification Structure

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Bead-on-plate welding was performed on thin sheets of 99.96%-, 1050-and 1100-aluminum using GTA (dcrp). Microsegregation was investigated in the weld metal of these materials. Using X-ray diffraction the compounds of Al-Fe and Al-Fe-Si type were identified in a commercially pure aluminum. It was observed that iron segregated along subboundaries inside of the columnar crystal and the equiaxed dendrite using electron probe microanalyser. The amount of segregaion of iron along the grain boundary of the columnar crystal was almost the same as along subboundaries. Then investigation was made on the distributions of compounds and dislocations in the weld metal using transmission electron microscope. Subboundaries in 99.96%-aluminum consisted of dislocations parallel to the growth direction of the subgrain and no compound was observed in this case. In the commercially pure aluminum subboundaries consisted generally of both compounds and dislocations. The compound developed along subboundaries was identified as Al_3Fe using selected area diffraction.