Grain refining aluminium foundry alloys with commercial Al–B master alloys

Abstract

In Al–3B master alloy, a higher fraction of borides is of the AlB2 variety, while in Al–8B alloy, the predominant species is the AlB12 phase. AlB12 is less stable than AlB2 and is engaged in exchange reactions, leading to the formation of transition metal diborides that subsequently settle at the bottom of the melt. Hence, AlB12 is involved more in precipitating transition elements than in refining the grain structure. With predominantly AlB12 particles, Al–8B master alloys are better suited for the removal of transition metal impurities in the manufacture of aluminium conductors. Al–3B, on the other hand, is a better grain refiner as the majority of its borides are of the AlB2 variety. Which of the two master alloys is used in grain refinement does not make a difference once the transition metal impurities have been precipitated. B is dedicated to grain refinement in an impurity free aluminium melt and produces exceptionally small equiaxed grains across the section of the samples.

Grain refining AlSi7Mg0·3 foundry alloy with commercial Al–4B master alloy

“…When added into molten aluminium, B reacts with Ti and other transition elements since their borides are more stable than those of aluminium and are separated by gravity settlement. 28,29 Hence, the concentrations of the transition elements present in the alloy ingot were first measured with optical emission spectroscopy. The concentration of B that would readily react with these elements was calculated assuming that B would form diborides with Ti, Zr and V, namely, TiB 2 , ZrB 2 and VB 2 respectively, and SrB 6 , with Sr. Once the B concentration required to form these borides were estimated, two addition rates were calculated by adding to this sum extra concentrations of 250 and 500 ppm B (Table 1).…”

“…[22][23][24][25][26][27] B addition was shown to be very effective in grain refining Ti free Al-Si foundry alloys. 7,14,28 Commercial foundry alloys, on the other hand, contain as much as 0?04-0?1 wt-%Ti and suffer from Ti poisoning when inoculated with Al-B master alloys. It is thus of great technological interest to find out if and how commercial foundry alloys with substantial Ti can be grain refined with Al-B master alloys, which are marketed to precipitate Ti rather than to refine the grains.…”

Bor Katkılarının Al-30Zn Alaşımının İçyapı ve Mekanik Özelliklerine Etkisinin İncelenmesi

“…çekirdekleri oluşurken bu bileşik sıvı içinde kalmaya devam etmektedir. Diğer taraftan, AlB 2 bileşiğinin tam olarak kararlı bir faz olmaması [51,52], sıvı içerisindeki AlB 2 bileşiği ile sıvı faz η arasında çözünürlükle ilgili Hume-Rothery ilkelerinin [53] önemli ölçüde sağlanması ve bunlara ilave olarak indüksiyonla ergitme nedeniyle ergitme anında sürekli karıştırma [44,54]…”

Tailoring the tensile properties of AZ91 magnesium alloy via grain refinement

“…The master alloys containing Al, Ti, and B are commonly used for inoculation, where the formation of inoculants such as TiB 2 , TiAl 3 , and AlB 2 has been noted [14][15][16]. Among the abovementioned master alloys, the Al-B variants such as Al-4 wt-% B have shown good grain refining performances [16][17][18]. Both matrix and AlB 2 have a hexagonal structure with similar lattice parameters, and high melting point AlB 2 shows good stability in the Mg melt, suggesting that AlB 2 is an effective inoculant for α-Mg [16].…”