Air Oxidation Welds:

Air oxidation weld flashes are mostly distributed on the upper surface of the casting, at the corners where the metal mold is not ventilated. The fracture surface is mostly gray-white or light yellow, which can be found by X-ray fluoroscopy or machining, and can also be found in alkali washing, pickling passivation or anodizing treatment.

Cause:

• The returning waste is not cleaned up, and the demand for returning waste is too much
• Poor design of pouring control system
• The slag in the aluminum alloy liquid is not cleaned up
• The actual operation of pouring is not good, which leads to the welding bump
• Insufficient standing time after scouring and metamorphism.

Ways to avoid:

• The returned waste should undergo sand blasting, and the demand for returned waste should be moderately reduced
• Improve the design of the pouring control system and enhance its slag blocking ability
• Use a moderate solution to remove slag
• It should be stable when pouring and should pay attention to slag blocking
• After scouring, the aluminum alloy liquid should be placed for a certain period of time before pouring.

Vent bubble

The vent holes in the wall of the casting are generally round or oval, with a smooth surface, usually a luminous oxide skin, and sometimes oily yellowish. Surface vent holes and bubbles can be found by sandblasting, and internal vent holes can be found by X-ray fluoroscopy or machining.

Air vent bubbles appear grey-black on X-ray film pictures

Cause:

• The cast aluminum alloy is unstable and is involved in the vapor
• Organic chemical residues (such as coal dust, grass-roots entrepreneurial horse manure, etc.) infiltrated into the sand (core)
• Poor ventilation of metal molds and sand cores
• There is shrinkage on the surface of cold iron
• Poor design of pouring control system.

Ways to avoid:

• Properly grasp the pouring rate to prevent the vapor from being involved.
• The organic chemical residues cannot be infiltrated into the molding (core) sand to reduce the air supply of the modeling and design raw materials
• Improve the working ability of the exhaust pipe of (core) sand
• Proper adoption and solution of cold iron
• Improve the design of the pouring control system Three shrinkage porosity Disadvantages: The shrinkage of aluminum alloy die castings generally results in the thick and large position at the root of the fly gate around the inner sprue, the thin-thick wall connection and the thick wall with a large plan.

Fracure surface is dark gray

In the as-cast state, the fracture surface is dark gray, and the light yellow is grayish white, pale yellow or black gray after tempering treatment. It is cloudy in the X-ray film. The more serious flocculent shrinkage can be obtained according to the high magnification of X-ray and fluorescent light. Inspection methods such as fracture surface

Cause:

• Poor gate feeding effect
• Too much gas supply in the returned waste
• Over temperature around the inner sprue
• There is too much water in the sand mold, and the sand core is not air-dried
• Aluminum alloy crystal is thick
• The location of the casting in the metal mold is not good
• The pouring temperature is too high and the pouring rate is too fast

Ways to avoid:

• Refill the metal material liquid from the gate to improve the gate design
• The returned waste should be cleaned for corrosion resistance
• Set the gate at the shrinkage of the casting, and place the cold iron or the cold iron together with the gate
• Control sand moisture, and sand core dryness
• Adopt measures to optimize grain size
• Improve the position of the casting in the metal mold, reduce the pouring temperature and pouring rate

Conclusion

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