Why Does Molten Aluminum Need Filtration?

The primary purpose of filtering molten aluminum is to remove solid inclusions (impurities) from the molten aluminum and improve the quality of aluminum castings and aluminum profiles; otherwise, impurities remaining in the finished products will cause various defects.

What Impurities Are Present in Molten Aluminum?

1. Aluminum oxide (Al₂O₃, aluminum dross, oxide film): Aluminum reacts easily with air, forming a crust of oxide on the surface of the melt. During stirring and transfer, this crust breaks up and mixes into the molten aluminum, forming fine oxide inclusions.

2. Refractory particles, such as particles of refractory mortar that have peeled off from the linings of furnaces and flow channels.

3. Carbides, intermetallic compounds, and other small solid particles such as sand, silt, and tool debris that have been introduced into the melt.

Solid impurities in molten aluminum—such as oxide films and refractory particles—remain inside aluminum products, creating stress concentration points that reduce the material’s tensile strength and elongation, making the products prone to fracture.

These impurities also cause casting defects such as inclusions, cracks, and peeling, resulting in failure to pass non-destructive testing. During extrusion and rolling processes, hard impurities can scratch the dies, creating surface defects on the aluminum material.

Additionally, electrochemical corrosion is likely to occur at the locations of these impurities, reducing the product’s corrosion resistance, significantly increasing the scrap rate, and failing to meet the quality requirements for high-end aluminum materials used in the automotive, power battery, and aerospace industries.