Microstructure refinement and corrosion resistance improvement mechanisms of a novel Al-Si-Fe-Mg-Cu-Zn alloy prepared by ultrasonic vibration-assisted rheological die-casting process

Abstract

The Al-Si-Fe-Mg-Cu-Zn alloy was used to manufacture large, thin-walled parts for 5 G base stations by using the ultrasonic vibration-assisted air-cooled stirring rod rheological die-casting (ACSR + UV R-DC) process. Investigations were performed on the microstructure and corrosion resistance of the ACSR + UV R-DC alloy which was then compared with traditionally die-casting (T-DC) and ACSR R-DC alloys. The results reported that the ACSR + UV R-DC process not only refined the primary α-Al (α1-Al), the eutectic silicon, and the secondary α-Al (α2-Al), but also significantly improved the morphology and distribution of the β-Al5FeSi phase. Pitting corrosion of the alloy mainly originated from the interface between the β-Al5FeSi and the α2-Al. At the initial corrosion stage, the α1-Al and the interface between the α2-Al and the eutectic silicon were not corroded. As the corrosion time increased, the pitting corrosion continued to spread in the eutectic region and connected to form one large corrosion area. Moreover, the corrosion resistance of the ACSR + UV R-DC alloy was better than that of the T-DC and the ACSR R-DC alloys. This was due to the refinement of the eutectic silicon and iron-rich phases, and the reduction of the potential difference between the iron-rich β-phase and the aluminum matrix.