Effect of Sc and Zr on Precipitation Behaviour of Wrought Al- Bronze

Abstract

Aluminium bronze doped with Sc and Zr were prepared by casting followed by cold-rolling with varied degrees of deformation. Then, the cold-rolled samples were aged for one hour at various temperatures, isochronally up to 500°C and isothermally at 300°C and 350°C up to four hours respectively. To better understand the precipitation behavior of Al-bronze with Sc and Zr additions, microhardness and electrical resistivity of aged alloys were investigated. The formation of copper aluminates precipitate resulted in a significant hardening improvement in aged alloys particularly at 300 °C. The addition of both Sc and Zr improved the thermal stability of the aged alloys by forming Al3Sc and Al3Zr precipitates. Sc, on the other hand, had proven to be more effective at improving aging behaviour of Al-bronze alloy. Electrical resistivity was also observed to increase with increasing aging temperature, then decrease slowly due to the production of fine precipitates and coarsening of this precipitate by over ageing, respectively. The DSC investigation supported the precipitation response by demonstrating the varied peaks of the heating curve at various temperatures. The reflectance spectroscopy study revealed that the addition of Sc and Zr exhibited greater optical response owing to grain refinement. Optical microscopy of cold rolled samples exhibited multiple phases of elongated grain along the rolling direction, and Sc and Zr additions were capable of refining alloy grains by precipitation of primary Al3Sc and Al3Zr particles formed as heterogeneous nuclei during solidification. In the meantime, recrystallization and grain growth development were induced in Al-bronze by ageing at 500°C for an hour. During ageing treatment, the production of secondary Al3Sc and Al3Zr precipitates efficiently inhibited the mobility of dislocation and sub-grain boundaries, preventing the Sc and Zr doped alloys from recrystallization.