Effect of Mixed Rare Earth on the Iron Phase and Tensile Properties in Squeeze Casting 6066 Aluminum Alloys

The microstructures and mechanical properties of Al-Si-Mg-Cu-Mn alloys that were squeeze-casted with varying La-Ce mixed rare earth content were analyzed by testing tensile strength and hardness and examining microstructures using various methods such as the optical microscopy, scanning electron microscopy, energy dispersive spectrum spectroscopy, and image analysis. The experimental results revealed that the elongation was affected by the iron content and the Chinese script iron phase showed less damage to the elongation compared to other blocky iron phases. The rare earth element Ce reacts with Al₂O₃ to form Ce₂O₃, which can act as a heterogeneous nucleating agent for α-Fe. This is because of the two-dimensional lattice mismatch between the \({(0001)}_{{\text{Ce}}_{2}{\text{O}}_{3}}\) ${(0001)}_{{\text{Ce}}_2{\text{O}}_3}$ and \({(111)}_{\alpha -Fe}\) ${(111)}_{\alpha -Fe}$ , which is specifically 4.5%, which is less than 12%. As the amount of α-Fe increases, the Fe content around the growth of the iron phase decreases. Meanwhile, the rare earth adsorbed on the iron phase would inhibit preferential growth and promote isotropic growth. With an increase in mixed rare earth content, the Chinese script iron phase would transform into a round and fine blocky shape. As a result, the fracture mode shifted from a combination of ductile and brittle fracture to a brittle fracture, accompanied by a transition from transgranular cleavage to transgranular–intergranular cleavage. At a mixed rare earth content of 0.07%, the material exhibited the best comprehensive properties after heat treatment, with a tensile strength of 371.7 MPa, yield strength of 285.7 MPa, and elongation of 4.2%. When the rare earth addition was 0.37%, the hardness of 6066 aluminum alloy reached the maximum value of 123.5 HBW.