Improved halide salt process to produce Al–B master alloys

Abstract

Adding KBF₄ salt to molten Al produces a B lean Al–B melt and a B rich dross. A revised practice that relies on the co-addition of Na₃AlF₆ with KBF₄ and mechanical stirring is proposed in the present work to produce Al–B alloys. The highly surface active Na₃AlF₆ helps to break up the boride agglomerates glued together by the spent salt. Mechanical stirring facilitates uniform distribution of the freed borides in molten aluminium. The microstructural features of the Al–3B alloy thus processed and the B recovery were improved in a marked fashion. The boride dispersion in the aluminium matrix was uniform with no evidence of salt residues inside the aluminium matrix. An improved salt addition practice to ensure full B recovery and an Al–B alloy of sufficient quality is thus claimed to comprise the following steps: melting commercial purity aluminium ingot, adding premixed KBF₄ and Na₃AlF₆ salts to molten Al at 800°C gradually to avoid excessive cooling of the melt, holding the melt for 5 min at 800°C to allow the reaction to reach completion, decanting the spent salt and throughly stirring the melt before casting into desired shape.