Investigation of the microstructure and corrosion properties of friction stir processed cast NiAl bronze

Abstract

NiAl bronze (NAB) was produced using the friction stir processing (FSP) technique at various tool rotation rates (ω) and traverse speeds (v). Optical microstructure (OM) observation results indicated that inhomogeneous microstructures were produced from top to bottom in the stir zone (SZ), cavity defects were found in the retreating side (RS) area due to inadequate fill of NAB material flow during FSP. Results indicate that FSP processing parameters have a significant influence on the microstructure of NAB alloy. An optimized FSP processing map was obtained from the analysis of the pseudo heat index ω2/v. Five optimum processing parameters were selected from the processing map, which were used to investigate the effect of FSP parameters on the corrosion properties of NAB by the salt fogging corrosion test. It was determined that the corrosion properties were improved by decreasing the rotation rate at a constant traverse speed, and the grain size and the volume fraction of retained β phases were reduced by using the optimum FSP parameters. These results could optimize the microstructure and deepen the understanding of the corrosion behavior of FSP NAB.