Melt treatment of Al–Si foundry alloys with B and Sr additions

Abstract

Individual Sr and B additions to Al-Si alloy melts fail to provide either grain refinement or modification. Sr and B must be used together to achieve both features for high-quality sound castings. Sr and B solutes in addition to insoluble SrB 6 particles are introduced to the melt when Sr and B are used together. SrB 6 particles and B solutes, which form the AlB 2 particles later during solidification, are believed to be responsible for the marked improvement in grain refinement in the co-addition practice. Sr atoms in liquid solution, on the other hand, are adsorbed on the surface of the Si plates leading to twinning once the melt cools to the eutectic solidification temperature. A series of experiments have shown that a very fine grained matrix and a fine fibrous eutectic are readily obtained when the AlSi7Mg0.3 alloy is inoculated with 100 ppm B and 150 ppm Sr.

Macro-, meso- and microstructural characterization of metallic lattice structures manufactured by additive manufacturing assisted investment casting

“…8 b). It appears that the solution treatment was able to coarsen and spheroidize the eutectic Si by self-diffusion and inter-diffusion 82 , transforming the characteristic fibrous/coral shapes towards a more round configuration after solution treatment 83 . The success of the solution treatment may also be attested by the absence of Mg 2 Si, indicating that it was fully dissolved by the α-Al matrix.…”

Si poisoning and promotion on the microstructure and mechanical properties of Al–Si–Mg cast alloys

“…The exact mechanism of grain refinement under Al5Ti1B has been well demonstrated recently; the formation of a monolayer of (112) Al 3 Ti two-dimensional compound on the (0001) TiB 2 surface can reduce the misfit between TiB 2 and a-Al from -4.2 to 0.09%, which can efficiently enhance the nucleation potency of TiB 2 particles for primary aAl grains [12]. The Al5Ti1B master alloy offers good performance in the casting of wrought alloys, but it is hard to meet the expectations in cast Al-Si alloys, especially with a content of Si higher than 3.5 wt% [13][14][15].…”

“…Grain refinement has been proved as an important way to obtain fine primary aAl grains, which can improve the toughness, strength, formability and machinability [1][2][3][4][5][6][7][8][9][10][11].…”

Preparation and Microstructure of In Situ CaB6–Al4Ca/Al Composite Inoculant Ribbon and Its Refining and Modifying Effect on Al–10Si–0.3Mg Alloy

“…With this simple crystallographic structure, the hexaborides of the alkaline and rare‐earth elements have been widely concerned by all sectors of society due to their various physical properties, such as high melting point, excellent chemical stability, low work function, and low expansion coefficient . According to the edge‐to‐edge matching model, the hexaborides of the alkaline and rare‐earth elements such as LaB 6 , CeB 6 , and SrB 6 , have been proven to be effective heterogeneous nuclei for α ‐Al, because the crystal lattice mismatches between LaB 6 , CeB 6 , SrB 6 , and α ‐Al are all less than 5% . To our knowledge, CaB 6 has a proper density (2.45 g cm −3 ), high melting point (2235 °C), high Young's modulus and great chemical stability.…”