Development of a lean electrically conductive Al-Zr alloy through Sn micro-alloying

With the rapid development and production of electric vehicles (EVs), the need for a lower density replacement for Cu components has become obvious. The high electrical conductivity and low density of lean Al-Zr alloys makes it a good candidate for replacing the existing Cu alloys that dominate conduction in EVs. The precipitation of the coarsening-resistant metastable Al₃Zr L1₂ phase provides age-hardening and reduces the detrimental effects of the Zr solute atoms on electrical conductivity. It has been observed in other aluminum alloy systems that micro-alloying additions of Sn can modify precipitation behavior to produce a stronger age hardening response. In this work, the influence of 0.09 wt% Sn (0.02 at%, 200 ppm) additions on the hardness and electrical conductivity is investigated via isochronal and isothermal aging of a lean Al-Zr alloy between 150 ˚C and 550 ˚C. Selected specimens were investigated with scanning transmission electron microscopy (STEM), atom probe tomography (APT), and small angle x-ray scattering (SAXS). A mechanism for heterogenous nucleation due to the formation of Zr-Sn-vacancy clusters is proposed based on advanced characterization and a density functional theory (DFT) model. It is demonstrated that Sn additions have a beneficial influence on the balance of mechanical and electrical properties in this lean Al-Zr alloy.