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Solutions for "Hard Spots" in Aluminum Alloy Die Castings

Solutions for "Hard Spots" in Aluminum Alloy Die Castings

Solutions for "Hard Spots" in Aluminum Alloy Die Castings

Hard spots in die castings are a casting flaw that aluminum die casting factories encounter during processing. The casting has small spots that are harder than the metal matrix, which may be oxidized and doped or slag inclusions. Therefore, hard spots will cause severe tool wear and increase processing difficulty. 

After processing, more hard spots of different brightness will appear on the aluminum alloy die casting.

Ⅰ. Causes of non-metallic hard spots of aluminum alloy die castings and preventive measures:


1. Mixed with oxides on the surface of the alloy liquid.

2. The aluminum alloy is poured on the liquid plate.

3. The reaction product of alloy liquid and mold release agent is mixed.

4. Mixed with the mixture of alloy liquid and refractory materials.

5. Produce compatible compounds such as aluminum, manganese, iron, silicon.

6. Silicon is free, or the amount of Si in the alloy exceeds 11.6%, and the content of Cu and Fe is also high.


1. Do not scoop the oxide on the surface of the alloy liquid into the spoon.

2. After removing the oxides on the surface of the iron crucible, paint again.

3. Remove oxides on spoons and other tools.

4. Use paint that does not chemically react with aluminum.

5. Use refractory materials and mortar that do not react with aluminum alloys, such as aluminum oxide materials.

6. Regularly replace the furnace lining material.

7. When aluminum alloy contains Mn, Fe, Si, and other elements, segregation should prevent.

8. Use a dry degassing agent to degas, but the magnesium content in aluminum alloy should compensate.

9. When the aluminum alloy contains a large amount of Cu, Fe, the mass fraction of Si should reduce to below 10.5%.

10. Properly increase the pouring temperature to avoid the precipitation of Si.

11. Strengthen management and strictly prevent foreign matters or other materials from existing mixed into the foundry returns.

12 Do not stick oil, sand, dust on the charge.

13. Clean the rust and oxide on the crucible and melting tools.

Ⅱ. Causes of hard metal spots on aluminum alloy die castings and preventive measures:

1. It is mix with crystalline materials that produce intermetallic compounds.

2. Mixed with undissolved silicon material.

3. Mixed with raw materials that promote the growth of primary silicon crystals.


1. Do not use silicon element powder for aluminum-silicon alloy.

2. When adjusting the alloy composition, do not directly add Si but use an intermediate alloy.

3. The smelting temperature should be high, and the time should make the Si completely dissolve.

4. Reduce the fluctuation range of casting temperature and keep it in a molten state.

5. When adding cold material, prevent the alloy ingot from solidifying the alloy liquid.

6. Minimize the ingredients that promote the easy growth of primary crystal silicon.

7. Reduce the temperature fluctuation range, and don't take the temperature of the alloy liquid too high or too low.

8. Control the content of impurities in alloy components.

9. The materials that can produce intermetallic compounds should be smelted at high temperatures. To prevent the increase of impurities, they should add in small amounts.

10. After the alloy liquid add to the pressure chamber, it should be injected and filled immediately.

11. Try not to contain Ca, Mg, Na, and other alloy components that are likely to cause rapid cooling effects. The mass fraction of Ca should control below 0.05%.

The above is the analysis of the hard points of the die-casting parts by the aluminum die-casting factory. We strictly abide by the requirements for the production of aluminum alloy die castings to ensure the quality of the die castings.

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