Production of Al-B alloy by heating Al/KBF4 powder blends

Al-B master alloys have received considerable attention in recent years owing to their potential as efficient grain refiners for aluminium foundry alloys. While they are generally produced via the halide salt route in bulk alloy form, their use in the form of compacted alloy tablets would be more attractive in aluminium foundries. In the present work, the response to thermal exposure of Al/KBF4 powder blends was investigated in an effort to explore the potential of powder metallurgy processing in the production of Al-B master alloys. KBF4 starts to react with aluminium at temperatures as low as 490 degrees C. well below the melting point of aluminium. Reduction of KBF4 salt by aluminium produces AlB2 particles in aluminium grains and KAlF4 salt dispersed in between. The former are in the form of clustered stringers marking the counters of the original powder grains in mixed Al/KBF4 samples. AlB2 particles are dispersed more homogeneously in ball-milled samples owing to the dispersion capacity of the high energy milling process. No evidence of the AlB12 phase, often reported to be present in Al-B master alloys, was noted in heat treated powder blend samples. (C) 2009 Elsevier B.V. All rights reserved.