Air oxidation black spots on aluminum alloy die casting parts can be caused by a variety of factors, and addressing these issues typically requires a combination of preventive measures and corrective actions. Here are some common reasons for air oxidation black spots and potential solutions:

1. Contaminated or Poor-Quality Alloy:

   • Reason: Contaminants or impurities in the aluminum alloy can lead to black spots during oxidation.
   • Solution: Ensure that you use high-quality, clean aluminum alloy for die casting. Properly monitor and maintain the alloy's purity.
     
     

2. High Casting Temperature:

   • Reason: Casting at excessively high temperatures can promote air oxidation.
   • Solution: Control the die casting process by monitoring and adjusting the casting temperature to an optimal range, which is specific to the alloy being used.
     
     

3. Inadequate Die Lubrication:

   • Reason: Poor die lubrication can lead to increased friction and heat, which can promote oxidation.
   • Solution: Implement a regular and effective die lubrication schedule to reduce friction and heat. Use suitable lubricants that are appropriate for the specific die casting process.

4. Air Entrapment:

   • Reason: Air trapped within the die cavity can cause black spots as it reacts with the molten alloy.
   • Solution: Ensure proper venting and gating designs in the die casting mold to allow air to escape. Regularly inspect and maintain molds to prevent air entrapment.
     
     

5. Moisture in the Mold Cavity:

   • Reason: If moisture is present in the mold cavity, it can react with the molten alloy and cause black spots.
   • Solution: Store and handle the molds in a dry environment, and preheat them to remove any moisture before casting.
     
     

6. Oxidation of the Melting Furnace:

   • Reason: Oxidation of the furnace or crucible can introduce contaminants into the molten metal.
   • Solution: Regularly clean and maintain the melting furnace to minimize oxidation. Use proper fluxes and degassing agents to reduce impurities.
     
     

7. Inadequate Degassing:

   • Reason: Inadequate removal of dissolved gases from the molten metal can lead to black spot formation.
   • Solution: Use effective degassing techniques and equipment to eliminate dissolved gases before casting.
     
     

8. Improper Cooling Rates:

   • Reason: Rapid cooling of the casting can promote black spot formation.
   • Solution: Control the cooling rate to ensure gradual solidification of the casting, reducing the risk of black spots.
     
     

9. Mold Design and Venting:

   • Reason: Poor mold design and inadequate venting can lead to air oxidation.
   • Solution: Ensure that the mold design allows for proper venting and minimizes the risk of air entrapment. Consider using vacuum-assisted die casting to remove air from the cavity.
     
     

10. Quality Control and Inspection:

    • Reason: Inadequate quality control measures and inspection processes may result in black spots going unnoticed.
    • Solution: Implement rigorous quality control and inspection procedures to detect and address black spots during or after casting.

It's important to analyze the specific circumstances and production processes in your facility to identify the root causes of air oxidation black spots and implement appropriate solutions. Regular maintenance, monitoring, and process optimization are key to preventing these defects in aluminum alloy die casting parts.