Industrial Grade Aluminium Refine Flux for High Degassing Efficiency and Hydrogen Removal in Molten Aluminium

Aluminium refine flux is a solid, powdery, or granular chemical compound (or mixture of compounds) used during the melting and holding of aluminium and its alloys. Its primary purpose is to remove dissolved hydrogen gas and non-metallic inclusions (like oxides, carbides, and nitrides) from the molten metal.

Think of it as a "detergent" or "purifier" for molten aluminium.

Molten aluminium is highly reactive and readily reacts with the atmosphere (especially water vapor - H₂O) leading to two major defects in the final cast product:

• Porosity (Hydrogen Gas): Molten aluminium can dissolve hydrogen. When the metal solidifies, the hydrogen's solubility drops dramatically, forcing it to bubble out. These trapped bubbles become pores in the casting, severely weakening its mechanical properties (like strength and ductility) and pressure tightness.
  • Source of Hydrogen: The main source is the reaction: 2Al + 3H₂O → Al₂O₃ + 6H
  • The atomic hydrogen [H] then dissolves into the melt.
• Inclusions (Oxides and other Impurities): Aluminum forms a stable oxide (Al₂O₃) on its surface. When the melt is disturbed (e.g., during charging or stirring), this oxide skin gets entrapped. These hard, abrasive inclusions act as stress concentrators, reducing the metal's fatigue life and machinability.

Flux works through a combination of chemical and physical mechanisms:

• Chemical Reaction:
  • Degassing: Many fluxes contain salts that decompose at molten aluminium temperatures. For example, fluxes with Hexachloroethane (C₂Cl₆) release chlorine gas (Cl₂). The chlorine bubbles then react with the dissolved hydrogen to form hydrogen chloride (HCl), which escapes to the surface.
    • C₂Cl₆ (s) → 2C (soot) + 3Cl₂ (g)
    • Cl₂ + 2[H] → 2HCl (g)
  • Alternative Degassers: Safer and more common modern fluxes use salts like Magnesium Chloride (MgCl₂) which release gases that perform the same function without the toxic chlorine fumes.
• Physical Action (Wetting & Agglomeration):
  • The molten flux forms a liquid slag layer on top of the melt, protecting it from further oxidation.
  • More importantly, the flux reduces the surface tension between the molten aluminium and the oxide inclusions (Al₂O₃). This allows the tiny, dispersed oxide particles to come together (agglomerate) and float to the surface, where they are absorbed into the slag layer (the dross). This slag is then easily skimmed off before casting.

Fluxes are often categorized by their primary function and chemical base.

Note: Most commercial fluxes are a blend of these components to provide multiple functions simultaneously.

Correct application is critical for effectiveness and safety.

• Preparation: The melt should be at the correct temperature (typically 700-750°C or 1300-1380°F). The flux should be dry to prevent introducing more moisture.
• Application Methods:
  • Rotor Injection (Most Effective): A rotating impeller is immersed into the melt, and a controlled stream of flux (or inert gas mixed with flux powder) is injected. This creates a fine dispersion of bubbles and ensures thorough contact with the entire melt volume. This is the standard in industrial foundries.
  • Plunging (Bell Method): The flux is placed in a perforated steel "bell" and plunged to the bottom of the furnace or ladle. As the bell is moved around, the flux decomposes and releases gas bubbles throughout the melt.
  • Simple Addition: For small-scale operations, flux can be sprinkled onto the surface and then raked or stirred in. This is less efficient but common in small foundries.
• Skimming: After a sufficient holding time (5-15 minutes), the now-dirty flux slag (dross) that has floated to the surface must be completely skimmed off. Leaving the used flux in the furnace re-contaminates the metal.
• Casting: The clean, degassed metal is then poured into molds.

In summary, aluminium refine flux is an essential chemical tool used to clean and degas molten aluminium, drastically improving the quality, integrity, and performance of the final aluminium castings. The choice of flux and application method depends on the specific alloy, the scale of operation, and the quality requirements.