Q1: How is bauxite refined into alumina?
Bauxite ore undergoes the Bayer process: crushed, mixed with caustic soda, and heated under pressure. This dissolves aluminum hydroxides, leaving impurities as "red mud" residue. After filtration, alumina (Al₂O₃) crystallizes from the solution. Calcination at 1100°C removes water, yielding white powder. Four tons of bauxite yield two tons of alumina.
Q2: What happens in the aluminum smelting process?
Alumina dissolves in molten cryolite within carbon-lined pots at 950°C. Direct current (150–500 kA) splits aluminum oxide into liquid aluminum and CO₂. Liquid aluminum sinks to pot bottoms, tapped every 1–2 days. Modern cells recover fluoride emissions, reducing environmental impact. It takes 13–15 MWh of electricity to produce one ton of aluminum.
Q3: How does continuous casting create aluminum products?
Direct Chill (DC) casting produces rolling ingots up to 30 tons for sheets/foil. Electromagnetic casting minimizes defects in high-purity slabs. Twin-roll casters solidify molten aluminum directly into 6-mm strip for cans. Homogenization at 600°C eliminates segregation. Scalping removes surface oxides before rolling.
Q4: What is aluminum extrusion?
Preheated alloy billets (400–500°C) are forced through steel dies via hydraulic rams. Complex cross-sections emerge at 5–60 m/min for window frames or heat sinks. Quenching locks in microstructure properties. Artificial aging (T5/T6 tempers) enhances strength. Precision cutting and surface finishing complete the process.
Q5: How is aluminum quality controlled?
Optical emission spectrometers verify alloy chemistry within 0.01%. Ultrasonic testing detects internal voids in aerospace billets. Tensile testers measure yield/ultimate strength per ASTM/ISO standards. Eddy-current probes check conductivity for electrical grades. Anodizing thickness is measured via destructive cross-section analysis.
