The poisoning effect of Sc or Zr in grain refinement of Al-Si-Mg alloy with Al-Ti-B

The effects of Sc or Zr on the grains of Al-Si-Mg alloy with Al-Ti-B addition were investigated under sand casting conditions by a polarizing microscope, differential scanning calorimetry and scanning electron microscopy. The results showed that the order of grain size is Alloy 1 (A357) < Alloy 3 (A357 + Zr) Alloy 2 (A357 + Sc), which meant that when Zr and Ti-B existed at the same time or Sc and Ti-B existed at the same time, the grain refinement effect of Zr, Sc and Ti-B can not be reflected, and the poisoning occurred. The order of the actual nucleation temperature of primary alpha-Al grains (Tl) was Alloy 1 Alloy 3 > Alloy 2. In Al-Si-Mg alloy with Ti-B, with added Sc or Zr, many intermetallic compounds containing Sc and Ti or Zr and Ti appeared, which meant that the content of Ti as nucleation cores in the melt decreased, and the poisoning occurred in the nucleation stage of grains.

Automated summary

When Ti-B is added to the alloy and Sc or Zr are present simultaneously, the grain refinement effect cannot be reflected and poisoning occurs. Alloy 3 has smaller grain size and higher nucleation temperature, with the presence of Sc or Zr affecting the content of Ti as nucleation cores, resulting in poisoning in the nucleation stage of grains.