Effects of Non-Metallic Inclusions in Molten Aluminum

Non-metallic inclusions in molten aluminum are mainly oxides. The harmful effects of oxides are mainly reflected in the following aspects:

1. Impact on Casting Performance

Oxides reduce the fluidity of aluminum alloy melt and weaken its ability to fill the mold. They also increase the tendency of the alloy to form dispersed shrinkage porosity and ingot cracks.

When there are many non-metallic inclusions in molten aluminum, the refining and degassing process during melting becomes more difficult. This can easily increase the number of inclusions in aluminum ingots or castings.

Oxides may directly form slag inclusions and oxide film defects in ingots or castings, reducing the yield of finished products.

2. Impact on Aluminum Product Quality

Oxides are an important cause of delamination and many surface defects in aluminum processed products. Their presence can seriously affect the quality of aluminum processing materials.

3. Impact on Heating and Heat Treatment

During heating and heat treatment, oxides can promote the formation of secondary porosity and bubbles.

4. Impact on Mechanical Properties

As the contamination level of aluminum alloy increases, the tensile strength and elongation of the alloy decrease. The reduction is especially serious in transverse elongation and dynamic mechanical properties, such as:

• Impact toughness
• Fatigue strength
• Fracture toughness

In addition, oxides can also reduce the stress corrosion resistance of aluminum alloys.

Why Is the Sodium Content High in Liquid Primary Aluminum?

In electrolytic aluminum production, cryolite is used as the main electrolyte raw material. Cryolite contains sodium fluoride. During electrolysis, sodium is decomposed and released.

Therefore, liquid primary aluminum in aluminum electrolytic cells contains a relatively high amount of sodium.

In electrolytic cells using strongly acidic electrolytes, the sodium content in liquid primary aluminum is relatively low.