Common Defects of Aluminum Alloy Gravity Casting


This defect often occurs in the thick part of the casting, or the intersection of the thickness and the thickness. Sometimes the surface of the casting is whitish, in fact it is shrinkage.


Insufficient casting shrinkage during crystallization;

The position of introducing alloy liquid is wrong;

The temperature of each part of the metal type is inappropriate and does not meet the principle of sequential solidification;

Improper paint or peeling paint;

Pouring temperature is too high;

The pouring speed is too fast;

The casting is cooling too slowly;

The burrs of the casting are too large.

Preventive measures:

Set the riser in the thick part of the casting, the size and height of the riser should be suitable, to achieve later solidification, and to improve the feeding effect of the riser;

Inner runners are evenly distributed along the circumference of the casting, or supplementary runners are opened from the root of the riser for supplementary pouring;

Adjust the temperature specifications of each part of the metal mold to facilitate the sequential solidification of castings;

According to the different requirements of the working part of the casting and the position of the pouring riser, different paint compositions and paint thicknesses are selected, and the stripping material should be evenly added;

Properly reduce the pouring temperature;

Slow down the pouring speed;

In areas prone to shrinkage, copper cold iron or vent plugs are embedded to accelerate cooling.

Second, cold partition

This type of defect usually occurs on thin-walled castings with a large horizontal surface, and where the alloy converges later. After casting, the sand is subjected to shock sand and visual inspection can be found.


Mold temperature is too low;

The temperature of the molten aluminum is too low;

Poor mold exhaust;

Poor design of the pouring system, the number of gates is small, and the cross section is too small;

The pouring speed is too slow or the pouring is interrupted;

The design thickness of the casting is too thin or lacks proper rounded corners.

Preventive measures:

Increase the mold temperature appropriately;

Properly increase the molten aluminum pouring temperature;

Ventilation slots or exhaust plugs are provided on the parts where the gas is not easily discharged to maintain good exhaust;

Increase the number of gates and the cross-section of gates appropriately;

Properly increase the pouring speed to avoid the interruption of molten aluminum pouring;

According to the technical requirements of casting design, design reasonable small wall thickness and casting fillet.

Three, stomata

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 seen through X-rays and when the casting is processed.


The pouring speed is too fast, which is involved in the air;

Poor exhaust gas from the mold;

Liquid aluminum flows too fast;

The melting temperature is too high;

Poor alloy degassing;

Pouring temperature is too high;

Sand core is not dry, poor exhaust or too much gas.

Preventive measures:

Pouring the molten metal smoothly;

Add exhaust slots or exhaust plugs to areas where metal-type gases are not easy to exclude, and clean them frequently;

When pouring, the ladle should be as close as possible to the gate cup;

Strictly control the temperature of aluminum liquid to prevent over-temperature;

Liquid aluminum is degassed correctly;

The mud core should be dried, the vent hole should be unblocked, the mud core should be re-baked after regaining moisture, and the middle of the large mud core should be hollowed out;

After the metal type coating, it should be poured after the coating is dry.

Four, crack

Most of the cracks appear at the internal angle of the casting, the transition between the thick and thin sections; where the alloy liquid is introduced into the casting and where the casting stress is greater, it can be found by color inspection, air tightness test, and X-ray inspection. Cold cracks on aluminum castings can be found by visual inspection after cleaning the sand core.


There are sharp corners on the casting, and the thickness is very different;

The mold is partially overheated or the pouring temperature is too high;

Cold iron is not installed correctly;

Poor shrinkage of castings;

Preventive measures:

Improve the design, remove the sharp corners of the casting, try to make the wall thickness of the casting uniformly transition and round the corners;

Correctly select the position of the gate and runner, control the pouring temperature and the thickness of the paint, place the cold iron correctly, and increase the feeding capacity of the riser;

Apply asbestos insulation coating on the riser of the mold.

V. Segregation

Segregation is generally distributed in the center and upper part of most of the thickness of the casting, which can be found when doing macro analysis.


The components of the molten aluminum are not evenly mixed before pouring;

Pouring temperature is too high;

The metal type temperature is too high, the coating is uneven and too thick.

Preventive measures:

Try to make the alloy liquid stir evenly before pouring;

Properly reduce the pouring temperature and the preheating temperature of the metal type;

Design cold iron, vent plug or use air cooling and water cooling in the slow cooling part;

Add elements that hinder segregation of the alloy;

The wall thickness of the casting is appropriately thinned to accelerate solidification.