Microstructure and corrosion resistance of commercial purity aluminum sheet manufactured by continuous casting direct rolling after ultrasonic melt pre-treatment

Abstract

During the new continuous casting direct rolling (CCDR) process for manufacturing commercially pure aluminum sheet for foils, casting defects tend to arise as the raw material with huge mass flow rapidly solidifies under a high cooling rate, which generates negative effects on the formability of aluminum sheets and the performance of final foil products. Therefore, melt pre-treatment during continuous casting is very essential to improve the quality of the billet. In this study, multi-source ultrasonic field was employed to pretreat an Al melt during the continuous casting stage in a Hazelett CCDR strip production line. The Ti content distribution in the melt, the microstructure and corrosion behaviors of the rolled sheet with and without ultrasonic melt pre-treatment (UMPT) were investigated. The microstructure of the rolled sheet was refined due to the increased Ti content and uniformly distributed Al3Ti particles under UMPT. In addition, the morphology of the Fe-containing secondary phase was modified from an aggregated to a scattered structure, with reduced continuity. As a result, under the combined effects of the refined α-Al grains and secondary phase, the corrosion resistance of the rolled sheet was improved. The underlying mechanisms for the modifications of the microstructure and corrosion resistance after UMPT are also interpreted, which gives theoretical guidance on the practical applications of the ultrasound-assisted continuous casting in industrial production.

Keywords

• Continuous casting direct rolling
• Ultrasonic melt pre-treatment
• Grain refinement
• Fe-containing phase
• Corrosion resistance