Efeitos da adição de Cr na evolução microestrutural e no comportamento mecânico de ligas Al–Ce e sua resistência ao envelhecimento térmico

Abstract

The development of aluminum alloys capable of operating between 250 °C and 400 °C remains challenging for commercial Al alloys due to rapid degradation of strengthening phases. The Al–Ce system emerges as a promising alternative because of the thermally stable Al₁₁Ce₃ intermetallic phase and the extremely low solubility and diffusivity of cerium in aluminum. This dissertation compares the Al–13 wt.%Ce and Al–10 wt.%Ce–1 wt.%Cr systems, evaluating the effect of cooling rate on solidification thermal parameters, microstructural evolution, and mechanical performance. Directional solidification experiments enabled correlations between growth velocity, cooling rate, thermal gradient, and dendritic and eutectic spacings. CALPHAD simulations predicted equivalent total intermetallic fractions for both alloys, while the ternary system exhibited the formation of primary Al₂₀CeCr₂. The eutectic morphology remained predominantly lamellar across the investigated cooling-rate range (0.7 to ~20 °C/s), with microstructural refinement directly governed by cooling conditions. Microhardness and compression tests showed improved mechanical performance at higher cooling rates due to refined intermetallic distributions and enhanced dislocation blocking. The ternary alloy exhibited superior compressive strength owing to the load-bearing contribution of Cr-rich primary particles. An automated digital image processing algorithm was also developed to quantify the morphological evolution of the Al–Al₁₁Ce₃ eutectic during aging at 400 °C for up to 100 hours. Results indicated high thermal stability, with subtle morphological changes and preservation of mechanical properties.