MICROSTRUCTURE AND TEXTURE ANALYSIS OF FRICTION STIR WELDS OF COPPER

摘要

Copper is readily joined by friction stir welding (FSW) due to its relatively low melting point. The stacking fault energy (SFE) of copper is comparatively low, resulting in a discontinuous dynamic recrystallization (DRX) mechanism operating at the temperature and strain rate range typical for FSW. To study the textures in the weld area, several FSWed copper (Cu-OFEP) samples were studied. A sample representing the optimum process conditions (tool temperature 850 °C) of a full scale 50 mm thick FSW weld of copper capsule for spent nuclear fuel was obtained from Swedish Nuclear Fuel and Waste Management Co (SKB). Smaller sized welds with varying processing parameters were also prepared to study the effects of the processing parameters deviating from optimal. The microstructure was studied with optical microscopy, FEGSEM and EBSD. New metallographical methods were developed to be able to distinguish the different zones in the weld area. The texture in FSW welds of copper is weak and it varies slightly according to the location in the weld, because the direction of the flow of material in FSW varies constantly in the weld area. The main texture component found in FSW welds of copper is < 101 > fibre texture.