Effect of Composite Refining Modifier on Microstructure and Properties of AlSi10Mg Alloy

In order to improve the effects of grain refinement, modification and refined degassing of Al-Si alloy synchronously, and to solve the problems of their mutual restrictions, the new type of composite refining modifier (K₂TiF₆, KBF₄, NaCl and KCl) was used to tailor the microstructure of AlSi10Mg alloy. Through varying the content of K₂TiF₆ and KBF₄, the effects of the composite refining modifier on microstructure and mechanical properties of AlSi10Mg alloy were investigated compared with the conventional C₂Cl₆ refining agent. The experimental results indicate that TiB₂ is formed in situ by K₂TiF₆ and KBF₄ at 800 °C. TiB₂ distributed in the melt acts as nucleation substrates for the primary Al (α-Al), which promotes the refinement transition of α-Al. The Na and K in the composite refining modifier jointly modify the eutectic Si. At the same time, the reaction products can remove gases and oxidized inclusions from the melt and play a critical role in refined degassing. Excellent mechanical properties can be obtained when K₂TiF₆ and KBF₄ account for 3.5 wt.% of the melt, with an increase in tensile strength and elongation of 33.1 and 126.9%, respectively, compared with adding 1.6 wt.% of C₂Cl₆ to the melt.