On the effect of praseodymium on solidification characteristics, microstructure, and mechanical properties of commercial ADC12 alloy

The effect of adding Praseodymium (Pr) with different percentages of 0.1, 0.3, 0.5, and 1% mass % on the solidification characteristics, microstructure, strength, impact energy, and hardness of ADC12 commercial alloy was evaluated. Examination of the three-dimensional morphology of Si by scanning electron microscopy (SEM) showed that by adding different percentages of Pr, the flake-like and needle structure of the eutectic Si did not change significantly. Cooling curve thermal analysis (CCTA) depicted that the growth temperature of Si decreased by less than 0.4° C, which was consistent with no change in the morphology of Si. The ultimate tensile strength, elongation percentage, impact energy, and hardness values were changed by 2.5%, 11.3%, 0.9%, and 1.5%, respectively, after adding 1 mass % Pr. Most of the fracture surfaces of the specimens were composed of cleavage, which indicated a brittle fracture mode proportional to small percentages of elongation. Based on the results, it can be concluded that Pr does not play the role of a modifier element for eutectic Si. The ratio of Pr radius to Si is 1.56, slightly less than the proposed value of 1.65 to modify based on growth theory. But elements with lower atomic radius ratios have changed Si. Therefore, growth theory alone can not be a reliable criterion for evaluating modification.