Friction stir processing and fusion welding in nickel aluminum propeller bronze

Abstract

Friction Stir Processing (FSP) is currently being developed for applications including as-cast Nickel- Aluminum Bronze (NAB). Fabrication and repair of the United States Navy's NAB propellers involve fusion welding of as-cast NAB and so it is probable that FSP is likely to encounter as deposited weld metal as well as the more slowly cooled as-cast material. Here, the microstructure and resulting distribution of mechanical properties was examined for a fusion weld overlay, an FSP stir zone and an FSP stir zone that was placed in fusion weld metal. As-deposited weld metal exhibited a refined WidmanstaÌ tten morphology and higher yield and ultimate strengths as well as increased ductility in comparison to base metal. However, the heat affected zone (HAZ) exhibited severely reduced ductility. Strength and ductility varied throughout the FSP stir zone. The reduction in ductility in the thermo-mechanically affected zone (TMAZ) and HAZ was less for FSP than for the fusion weld. FSP over a fusion weld resulted in strengths and ductility's similar to those produced by FSP alone, although a region of low ductility was observed at a location where stir zone weld metal and base metal were all present.