Study on the Enhancement of Al5Ti1B Refining Capacity by Rare Earth La and its effect on the Mechanical Properties of A6111 Aluminum Alloy

Abstract

In this study, a novel Al5Ti1B-xLa (x=1, 3, 5) refiner was prepared via the fluoride salt aluminum-thermal method (Al, KBF₄, K₂TiF₆) to investigate the effects of varying La concentrations on the refining phases Al₃Ti, TiB₂, and Ti₂Al₂₀La as well as on anti-fading capability, and to evaluate the influence of the refiner on the microstructure and properties of A6111 aluminum alloy. The results indicate that Al5Ti1B-1La exhibited the best refining performance and anti-fading capability. La suppressed the growth of Al₃Ti, and the core–shell structure formed by Ti₂Al₂₀La and Al₃Ti resulted in a more uniform distribution and denser microstructure of the secondary phases in Al5Ti1B-1La compared with commercial Al5Ti1B. TEM observations revealed that La was adsorbed on the TiB₂(0001) surface, forming Al–La two-dimensional compounds (2DC), which prevented the growth and agglomeration of TiB₂ particles. The addition of 1.0 wt% Al5Ti1B-1La successfully reduced the grain size of as-cast A6111 to 40.47±14.81μm, representing reductions of 80.7% and 47.8% compared with the unrefined alloy and commercial 1.0 wt% Al5Ti1B, respectively. After T6 heat treatment, the tensile strength, elongation, and hardness reached 320.2 MPa, 9.3%, and 98.6HV, respectively, corresponding to increases of 104.8%, 113.3%, and 32.7% over the unrefined alloy and 83.2%, 55.4%, and 18.1% over commercial 1.0 wt% Al5Ti1B. The fracture morphology transformed into ductile dimples. The introduction of La facilitated the transformation of β-Fe into α-Fe and converted the needle-like eutectic Si into short rod-like structures, thereby enhancing the mechanical properties of the aluminum alloy.