Production of aluminum alloys in electrolysis cells based on Hall-Héroult process: a review

Modern large-scale Hall-Héroult (H-H) aluminum electrolysis cells have super high amperage and a well-developed process technology; thus, they present great technical and economic advantages for the production of Al-based alloys. Compared with the traditional alloy production methods, H-H-based processes have a great potential in improving product quality, simplifying production process, and reducing energy consumption. In this review, the major achievements in the production of various common aluminum alloys, such as Al-RE (rare earth metals), Al-Mg, and Al-Si/Ti alloys using H-H-based processes, were summarized from the domestic and international literature. The main properties of cryolite-based electrolyte systems that determine whether the alloy production can proceed smoothly by H-H process were first discussed based on previous research results. Studies on the electrolyte structure, melting point, and conductivity of the cryolite-based electrolytes with varying compositions were described in details. For producing Al-based alloys, the conventional fluorides electrolytes can be modified by adding various oxides of alloying metals. The electrolysis mechanisms of cathode co-deposition and underpotential deposition are usually utilized with the addition of multiple metals oxides, and the electrolyte composition and processing parameters are appropriately adjusted in H-H-based processes. Moreover, the potential distribution in the interfacial reaction processes during electrolysis for the alloying process in electrolyte is proposed based on the existing electrochemical data. In addition, some industrial trials showed promising results for the future development. At present, these trials, especially for Al-Si and Al-Ti alloys, indicate that the contents of alloying elements can be stabilized within a certain range by adjusting electrolyte compositions, current density, feeding cycle, and other parameters. There are, however, problems associated with the accurate control of alloy compositions, the homogenous quality in bulk alloy products, and the electrolysis cell operation with high current efficiency. Further research is needed to address these problems.