Effect of End-of-Life (EOL) Content in High-Vacuum High-Pressure Die Cast (HVHPDC) A365-T7 on Corrosion Behaviour

Abstract

The recent awareness of global warming and climate change has triggered the idea of implementing End-of-Life (EOL) materials to fabricate secondary cast Al alloys; this is to further consider more sustainable manufacturing, which is also expected to reduce the greenhouse gas (GHG) emission of automotive component manufacturing. In this research, the effect of EOL materials implemented in high-vacuum high- pressure die cast (HVHPDC) A365-T7 alloy on corrosion behaviour was investigated. A365-T7 alloys with different EOL contents (0%, 40%, 75%, and 90%) were fabricated by Nemak Monterrey. The chemical composition of primary alloy and secondary alloys was comparable except for impurity elements such as Cu and Zn, and lower Ti content were observed in the secondary alloy. Corrosion experiments indicated that all secondary alloys were more susceptible to localized corrosion initiation, and the effect of EOL content in secondary alloys was found to be minor. Microstructure characterization revealed several features; the primary Al cell size of primary alloy at the skin region was smaller than ones observed in secondary alloys. Smaller fraction of Fe-containing intermetallic particles (IMPs) was also observed in the primary alloy. Passive film investigation was conducted on EOL 0 and EOL 40 (representing secondary alloys); Mg and Zn were detected on the passive film of EOL 40. Three working theories on localized corrosion initiation susceptibility were established: (i) effect of Fe-containing IMPs, (ii) effect of structure refinement (iii), and effect of Mg and Zn on the passive film. It was concluded that the localized corrosion initiation susceptibility of secondary alloy may be influenced by one or a combination of those working theories.This research investigated the effect of EOL materials on corrosion behaviour which is one of the most essential properties of cast Al alloys. Successful understanding of such effects would enhance the utilization of EOL materials.