Balancing Strength and Electrical Conductivity through Heat Treatment in an HPDC Al-3Si-0.5Mg-Ce Alloy
The rapid growth of electric vehicles (EVs) has increased the demand for high-performance materials capable of meeting the requirements of modern mobility. Certain applications, such as EV rotors, require aluminum alloys that combine high castability, high electrical conductivity (EC), and sufficient mechanical strength. Achieving these properties simultaneously is challenging for conventional Al cast alloys, as the mechanisms that enhance castability and strength often lead to a reduction in EC, making these requirements difficult to balance. In this study, a newly designed Ce-containing AlSi3Mg0.5 conductor alloy was produced by high pressure die casting (HPDC) and subjected to T5 and T6 heat treatments to improve both EC and strength. The objective is to establish practical heat treatment guidelines to obtain a balanced combination of properties for EV rotor applications. The results show that precipitation strengthening associated with Mg₂Si-type phases formed during T5 and T6 heat treatments, confirmed by transmission electron microscopy (TEM), contributes to increases in both strength and conductivity. For similar EC values, T6 samples exhibit higher strength but lower elongation compared with T5 samples over the aging time. Statistical analysis using a Weibull distribution indicates greater scatter in the mechanical performance of T6 specimens. Fractographic analysis further reveals a more brittle fracture behavior in some T6 samples, where large defects are observed on the fracture surfaces. These observations suggest that pore growth during the T6 heat treatment can reduce resistance to crack propagation, leading to reduced ductility and lower reproducibility of mechanical properties.
Key words: High pressure die casting, Al-Si-Mg alloy, Electrical conductivity, Heat treatment, Mechanical properties, Weibull distribution