Effect of the End-of-Life (EOL) Content in High-Pressure Vacuum-Assisted Die Cast (HPVADC) Aural2 (AlSi10Mg) on Corrosion Behaviour

Al cast alloys are widely used in automotive applications due to their high strength-to-weight ratio. The castability of Al alloy is known to be excellent; the idea of implementing the End-of-Life (EOL) Al alloy parts to fabricate new Al alloys is determined to be feasible. In contrast, the fabrication of Al cast alloys with the EOL content increases the propensity of introducing the impurity element to the Al cast alloys. It is expected to affect the microstructure such as the distribution and morphology of intermetallic particles. The mechanical properties of those alloys, also known as the secondary alloys, are comparable to primary alloys, however, the corrosion behaviour of secondary alloys is not fully characterized and understood. It is anticipated that the corrosion behaviour is affected by the EOL content introduced to the Al cast alloys. In this research, HPVADC Aural2 alloy with different EOL contents (0%, 40%, 75%, and 90%) are subjected to various electrochemical characterization techniques and microstructure characterization. Cyclic polarization measurements were conducted on both skin and core parts of the alloys. The breakdown potential (Eb) of the primary alloy was found to be the lowest, however, the potential difference between the breakdown (Eb) and repassivation (Er) of the primary alloy was significantly smaller than the secondary alloys. Potentiostatic polarization was also performed on both skin and core parts to observe the corrosion modes, and it was determined that both initiation and propagation corrosion modes were inter-granular/inter-dendritic corrosion. Galvanostatic polarization measurements were performed, and the behaviour of the potential responses differed between the primary and the secondary alloys, as well as the core and skin. Scanning Vibrating Electrode Technique (SVET) will be performed on the cross-section, skin, and core region to observe the local anodic/cathodic current density. The passive layer characteristics of each EOL alloy will be investigated by X-ray Photoelectron Spectroscopy (XPS). Microstructure analysis through Light Optical Microscope (LOM) and Scanning Electron Microscopy (SEM) was conducted. The distribution of Si eutectic and Fe-containing intermetallic particles on the secondary alloys was found to be different from the primary alloy; the mean size of intermetallic particles observed on the skin in the secondary alloys was higher than the primary alloy. No significant difference was observed at the core region in terms of intermetallic distribution. The morphology and chemistry of intermetallic particles will be further investigated with Energy Dispersive Spectroscopy (EDS). This research is conducted to characterize the effect of EOL content on their microstructures which is essential to understand the corrosion behaviour of the secondary alloys, ultimately enhancing the utilization of EOL parts in the Al cast alloy manufacturing.