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.

AlB3 master alloy to grain refine AlSi10Mg and AlSi12Cu aluminium foundry alloys

“…The AlSi10Mg and AlSi12Cu alloy ingots thus obtained, each weigthing 1000 g, were melted in a resistance furnace and the temperature of the melts thus obtained were brought to 750 • C. Grain refinement tests were performed with the AlB3 master alloy that contains only AlB2 particles in contrast to the AlTi5B1 alloy [14] (Fig. 1b).…”

“…The latter contain substantial levels of Si to improve castability. Si, the major ingredient of the foundry alloys, reacts with Ti to form Ti-Si binary phases at Si > 3 wt%, at the expense of Al 3 Ti and TiB 2 particles, thereby imparing the grain refinement efficiency [14][15][16][17]. In contrast to the wrought alloys which are grain refined adequately at Ti addition rates of 0.005-0.01 wt%, foundry alloys require at least 10 times * Tel.…”

“…The grain refinement of aluminium foundry alloys can be accomplished only with grain refiners that are potent in spite of high Si levels. While Al-B master alloys were shown to be more effective with Al-Si alloys [10,13,14,[18][19][20], the industrial practice today relies almost entirely on the AlTi5B1 grain refiner. The search for alternative grain refiners and more effective grain refinement practices has intensified in recent years [21][22][23][24].…”

Effect of Cryolite on Microstructure of Insitu AlB2 Aluminium Metal Matrix Composites

“…Genuinely uniform scattering of AlB 2 particles in Al6061 base matrix can be accomplished by stirring the melt persistently which helps in fracture of substantial agglomeration of boride particles into littler particles which can be consistently distributed in the matrix [47]. Figure .3.1 (e) and (f) pertain to micrograph when KBF 4 salt is premixed with the cryolite in the ratio of 1:2 wt.% of the reinforcement, fairly uniform dispersion of AlB 2 particles in Al6061 matrix can be achieved by stirring the melt continuously which helps in breakage of clustering of boride particles into smaller particles which can be uniformly distributed in matrix [48].It is also observed that low aspect ratio of AlB 2 particles distributed throughout the base matrix. For converting from low aspect ratio to high aspect ratio AlB 2 particles melt to be heated more than 950 0 C and to be cooled according to the Al-Boron binary phase diagram.…”

“…For converting from low aspect ratio to high aspect ratio AlB 2 particles melt to be heated more than 950 0 C and to be cooled according to the Al-Boron binary phase diagram. Even vigorous stirring is carried out during the chemical reaction in the melt, retaining of uniform distribution of AlB 2 particle is extremely impossible [49]. Depending upon the cooling rate, chemical reaction time and melt temperature reaction, the clustering of the inistu particles forms inside the matrix.…”