Common Defects Of Aluminum Castings And The Prevention Methods

Aluminum casting foundry is a new technology with electromagnetic pump low pressure Casting technology as the core, aluminum smelting and forming composite purification technology as the core of the manufacturing industry, producing high-quality aluminum Casting modern technology.The following are aluminum casting defects and aluminum casting solutions:

A, stomatal

Features: 1. The surface of hole wall is generally smooth with metallic luster.2. Singly or in groups or under the skin of the casting.3. Oil fume pores are oil-yellow.

Cause analysis: 1. The gas involved in the pouring of liquid metal exists in the casting in the form of porosity after the solidification of liquid alloy.2. Subcutaneous pores generated under the casting skin after the metal reacts with the casting mold.3. The slag inclusion in the alloy solution or the gas attached to the oxide skin is mixed with the alloy solution to form pores. 

Prevention methods: 1. Prevent air from getting involved during pouring.2. Before entering the mold cavity, the alloy liquid passes through the filter screen to remove slag, oxide peel and bubbles in the alloy liquid.3. Change the casting material or add coating layer to prevent the alloy liquid from reacting with the casting.4. Repair welding shall be carried out after the defects are cleaned up in the allowed repair welding area.

Second, the pinhole

Features: 1. Small holes (diameter less than 1 mm) evenly distributed over the whole section of the casting.2. There are fewer holes in the parts with fast solidification and more holes in the parts with slow solidification.3. Round holes in eutectic alloys and long holes in alloys with wide solidification intervals.4. Small black spots on the X-ray film and small non-continuous milky concave spots on the fracture.

Cause analysis: the gas (mainly hydrogen) melted in the liquid state of the alloy, and the evenly distributed holes formed by precipitation from the alloy during solidification.

Prevention methods: 1. Thoroughly refine and degas the alloy in liquid state.2. Increase the solidification speed during the solidification process to prevent the dissolved gas from precipitation from the alloy.3. The casting solidifies under pressure to prevent the alloy dissolved gas from precipitation.4. Charge, auxiliary materials and tools should be dried.

Third, loose

Features: 1. Spongy soft tissue, with shrinkage cavity in severe cases.2. The surface of the hole is rough pits with large grains.3. The fracture is gray or light yellow, and gray, light yellow or black after heat treatment.4. It is mostly produced at the hot spot.5. The X-ray film shows dense little bright spots when it is examined in a fog-like fluorescence.

Cause analysis: 1. The alloy liquid degassing is not clean, forming gas porosity.2. Finally, the solidified part is not enough to make up the shrinkage.3. Local overheating, excessive moisture and poor exhaust in the casting mold.

Prevention methods: 1. Keep reasonable solidification sequence and filling.2. Clean charge.3. Place chillers on loose parts.4. Repair welding can be carried out after cleaning up the defective parts where repair welding is allowed.

Four, the inclusion

Particles on the surface or inside of a casting that are different from the composition of the casting, formed by coating, molding materials, refractories, etc.

Cause analysis: 1. Foreign material was mixed with liquid alloy and poured into casting mold.2. Poor refining effect.3. Exfoliation of foreign objects or molding materials on the surface of the inner cavity of the cast mold.

Prevention methods: 1. Carefully refine and pay attention to dregs.2. The coating layer of smelting tools should adhere firmly.3. The casting system and cavity should be cleaned.4. Charge should be kept clean.5. Surface inclusion can be removed by grinding, and repair welding can be carried out if necessary.

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Aluminum Casting