MICROSTRUCTURAL DEVELOPMENT IN FRICTION STIR WELDING OF ALUMINUM ALLOYS

摘要

Typically, microstructural characterization of friction stir welds is done on a cross section of as-welded material. In this paper, a new approach is presented which allows one to obtain much more information on the effect of welding parameters on weld quality. In this approach, metallographic samples are taken from both as-welded and postweld heat treated welds. The metallographic samples are sectioned from the weld bead to include the exit hole which is left on the welded metal when pulling out a stir pin at the end of welding. Successive steps of polishing and examination, and re-polishing and re-examination of the same sample are then carried out so that the evolution of the microstructures and metal flow around the exit hole could be closely followed. Microstructural changes during friction stir welding and the occurrence of blistering in postweld heat treatment have also been discussed.