Jiangyin Jiada Machine&Electric Manufacture Co., Ltd.
English  |   Chinese
What are the common problems in gravity casting of aluminum alloys?

2023-06-27 11:51:39

1、 Porosity: Porosity often occurs in the upper part of the casting and often occurs on the surface of the protruding part of the casting. The hidden pores inside the casting must be detected through X-ray fluoroscopy and during the processing of the casting.

Reasons for occurrence: 1. The pouring speed is too fast, and air is drawn in; 2. Poor exhaust gas from the mold; 3. Aluminum liquid flows too fast; 4. The melting temperature is too high; 5. Poor degassing of alloy; 6. The pouring temperature is too high; 7. The sand core is not dry, the exhaust is poor, or the gas output is too large.

Prevention measures: 1. Pour metal liquid smoothly; 2. Install exhaust slots or plugs in areas where metal type gases are difficult to remove, and regularly clean them; 3. When pouring, the pouring ladle should be as close as possible to the pouring cup; 4. Strictly control the temperature of aluminum liquid to prevent overheating; 5. Correct degassing of aluminum liquid; 6. The mud core should be dried, and the exhaust hole should be unobstructed. After the mud core becomes damp, it should be dried again, and the middle of the oversized mud core should be hollowed out; 7. After the metal coating is applied, it should wait for the coating to dry before pouring.

2、 Cracks: Most of the cracks appear at the internal corners of the casting, as well as at the transitional areas between thick and thin sections; The parts where alloy liquid is introduced into the casting and the parts where casting stress occurs can be discovered through coloring inspection, air tightness test, and X-ray inspection. Cold cracks on aluminum castings can be detected through visual inspection after cleaning the sand core.

Reasons for occurrence: 1. There are sharp corners on the casting, resulting in a significant difference in thickness; 2. Local overheating of the mold or excessively high pouring temperature; 3. Incorrect placement of cold iron; 4. Poor shrinkage of castings;

Prevention measures: 1. Improve the design, make sharp corners of the casting, try to make the wall thickness of the casting transition evenly and chamfer corners; 2. Correctly select the gate and its position, control the pouring temperature and coating thickness, place the cold iron correctly, and increase the feeding capacity of the riser; 3. Apply asbestos insulation coating on the mold riser.


3、 Segregation: Segregation is generally distributed in the center and upper part of the thick part of the casting, and can be found during macroscopic analysis.

Reason for occurrence: 1. The aluminum liquid composition was not stirred evenly before pouring; 2. The pouring temperature is too high; 3. The temperature of the metal mold is too high, and the coating is uneven and too thick.

Prevention measures: 1. Try to stir the alloy liquid evenly before pouring; 2. Properly reduce the pouring temperature and preheating temperature of the metal mold; 3. Design cooling iron, ventilation plugs, or use air or water cooling in areas with slow cooling; 4. Adding elements that hinder segregation in the alloy; 5. Reduce the wall thickness of the casting appropriately to accelerate solidification.