Insights into the effects of La on the grain refinement and mechanical properties of Al-Ti-C intermediate alloy and pure Al: A first-principle study and experimental investigation

Abstract

This paper employs the self-propagating high-temperature synthesis (SHS) to prepare Al-Ti-C master alloys and explores the effects of integrating the rare earth element lanthanum to create Al-Ti-C-La composites. This research focuses on the microstructural changes in both the master alloy and pure aluminum, which aimed to elucidate the mechanisms that enhance grain refinement and resistance to grain refinement fading. The analysis reveals that when Al-Ti-C-La master alloys are incorporated into molten Al, the predominant structures formed include an Al matrix, rod-like Al3Ti phases, and TiC particles, alongside AlLa phases and substantial Al20Ti2La compounds. The grain refining capability of Al-Ti-C-La master alloys is significantly exceeds that of the Al-Ti-C master alloys. The addition of La markedly reduces the settling of TiC particles, thereby granting the Al-Ti-C-La master alloys excellent resistance to grain refinement fading. The newly formed Al20Ti2La phase plays a crucial role in refining the aluminum matrix, with metallic bond characteristics present on the side towards the Al matrix at the Al20Ti2La/Al interface and distinct covalent bond characteristics on the Al20Ti2La side. Moreover, the Al20Ti2La (110)/Al (110) interface exhibits the highest interfacial adhesion energy and stronger covalent bond features. Consequently, α-Al is prone to heterogeneously nucleate on the Al20Ti2La phase via the Al20Ti2La (110)/Al (110)-HCP orientation, which refines the grains of the aluminum matrix, ultimately enhancing the performance of aluminum-based alloys.