Grain refinement is an effective method to enhance the comprehensive properties of alloys. In industrial production, Al-5Ti-1B master alloys are commonly used to refine the microstructure of aluminum alloys. However, the grain refinement potency of Al-Ti-B master alloys is limited and cannot meet the requirements for high-performance aluminum alloy applications. It has been demonstrated that adding trace amount of micro-alloying element La to the aluminum alloy melt inoculated with Al-5Ti-1B master alloy can further refine the solidification microstructure. Previous research indicates that the addition of 0.06% (weight percent) La is sufficient to achieve an ideal α-Al grain refinement. Our recent experimental results demonstrate that for an Al-Mg alloy of high Mg content inoculated with Al-5Ti-1B master alloy, the optimal addition level of La is about 0.02% (weight percent).

Solidification experiments are carried out for Al-Mg alloys inoculated with Al-5Ti-1B master alloy and different addition levels of micro-alloying element La. It is demonstrated that the trace addition of micro-alloying element La shows a further grain refinement effect on Al-Mg alloy and reduces the nucleation undercooling of α-Al. A model is proposed for the segregation behavior of micro-alloying element La at the interface between the Al alloy melt and TiB₂. The mechanism of the enhancement in the efficiency of TiB₂ particles to nucleate α-Al by micro-alloying element La is clarified. The calculation results indicate that La shows a strong segregation tendency toward the interface between the Al melt and TiB₂ particles, thus reducing the interfacial energy and contact angle between TiB₂ and α-Al, enhancing the efficiency of TiB₂ to nucleate α-Al, and further refining α-Al grains.