The impacts of Co and Ni additions to high solute content Fe-contaminated Al alloys in beneficing microstructure and tensile properties

The accumulation of tramp impurities, particularly Fe, during recycling of Al alloys frequently leads to the production of coarse intermetallics during solidification, which affect final product mechanical properties. Because lowering the Fe concentration and/or using thermomechanical processing to subdivide the particles is expensive, it is preferred to modify the morphology, size, and distribution of the IMCs during solidification. Benefiting the properties of Al-contaminated alloys entails increased recyclability and a reduction in the usage of virgin primary Al and downcycled alloys. The Al-8%Si-0.8%Fe-2.5%Cu-1.0%Zn (in wt.%) alloy was modified with 0.7%Ni and 0.7%Co. Both dendritic growth and tensile properties were evaluated for the three alloys. The secondary dendrite arm spacing values (λ₂ ) were found very refined for all alloys. The λ₂ in the modified alloys was even more reduced. The Co addition of 0.7% reached higher values of tensile strength (220 MPa) as compared to the others without major losses in ductility. The addition of Co can enhance strength by up to 15%, considering more refined microstructures. (author)