10 Defects Analysis of Aluminum Die Casting

Die casting is a metal casting process, which is characterized by using a mold cavity to apply high pressure to the molten metal, similar to plastic injection molding. Die casting is particularly suitable for manufacturing a large number of small and medium-sized castings, so die casting is the most widely used in various casting processes. Compared with other casting technologies, the surface of aluminum die casting is smoother and has a higher dimensional consistency. However, non-standard operations and parameters can also cause many types of defects.

1. Flow Marks And Patterns

Visual inspection:

There are stripes on the surface of the casting that are consistent with the direction of the liquid metal flow, and there are obvious non-directional lines that are different from the color of the metal matrix.

The causes of flow marks are as follows:

1. The mold temperature is too low.
2. Poor design of the sprue and poor position of the inner gate.
3. The material temperature is too low.
4. Low filling speed and short filling time.
5. Poor pouring system.
6. Poor exhaust.
7. Unreasonable spray.

2. Net-shaped Hairy Fins (Turtle Crack)

Visual inspection:

The surface of the die casting part has raised or depressed traces like a mesh hairline, which continuously expands and extends as the number of die-casting increases.

The causes are as follows:

1. Cracks on the surface of the aluminum die casting cavity.
2. Uneven preheating of die casting mold.

3. Cold Partition

Visual inspection:

The surface of the aluminum die-casting parts has obvious, irregular, depressed linear patterns (both penetrating and non-penetrating). The shape is small and narrow, and sometimes the edge of the junction is smooth, and there is a possibility of disconnection under the action of external force.

The causes are as follows:

1. The two streams of metal are butted against each other, but they are not completely fused and there are no inclusions in between, and the bonding strength of the two metals is very weak.
2. Pouring temperature or aluminum die casting mold temperature is low.
3. The position of the sprue is wrong or the flow path is too long.
4. Low filling speed.

4. Collapse (Dent)

Visual inspection:

There are smooth dents (like disks) on the surface of most of the thickness of the aluminum die-casting.

The causes are as follows:

1. Unreasonable cooling system design
2. Premature mold opening
3. The pouring temperature is too high
4. Caused by shrinkage

      Improper design of aluminum die castings, wall thickness difference is too large.

      Improper location of sprue.

      The injection is lower than the pressure and the holding time is short.

      Die casting mold local temperature is too high.

5. Mark

Visual inspection:

The traces left by the surface of the casting and the surface of the aluminum die-casting mold cavity or the stepped traces appear on the surface of the casting.

The causes are as follows:

Caused by the ejection element

• The end face of the jack is worn.
• Adjusting length of jack is inconsistent.
• The splicing part of the aluminum die-casting model cavity does not fit well with other parts.

Caused by splicing or moving parts

• Part of the mosaic is loose.
• Loose or worn moving parts.
• The side wall surface of the casting is formed by inserts interpenetrating each other between the moving and fixed molds.

6. Traces of Adhesion

Visual inspection:

The small pieces and the metal or non-metal and the metal base are partially welded, and the small pieces are peeled off under the action of external force. The surface of the casting after peeling is shiny and dark gray.

The causes are as follows:

1. There are metallic or non-metallic residues on the surface of the aluminum die-casting mold cavity.
2. When pouring, first bring in impurities and attach to the surface of the cavity.

7. Layering (Skin And Peeling)

Visual inspection:

There are obvious levels of metal in the casting.

The causes are as follows:

1. The rigidity of the mold is not enough. During the filling process of the molten metal, the template jitters.
2. During the injection process, the punch appears crawling phenomenon.
3. Improper design of sprue system.

8. Friction Ablation

Visual inspection:

The surface of the aluminum die-casting part has a rough surface at certain positions.

The causes are as follows:

1. Improper position direction and shape of the inner runner caused by the aluminum die casting mold.
2. Insufficient cooling of molten parts at the inner runner caused by casting conditions is insufficient.

9. Erosion

Visual inspection:

There are pitting or embossing in the local position of the aluminum die casting.

The causes are as follows:

1. Improper setting of the inner runner.
2. The cooling conditions are not good.

10. Crack

Visual inspection:

Put the casting in alkaline solution, the crack is dark gray. The destruction and cracking of the metal matrix are linear or wavy, with narrow and long lines.

The causes are as follows:

1. The iron content in the alloy is too high or the silicon content is too low. The content of harmful impurities in the alloy is too high, which reduces the plasticity of the alloy. Al-Si alloy, Al-Si-Cu alloy contains zinc or copper content is too high. The aluminum-magnesium alloy contains too much magnesium.
2. The mold retention time is too short, and the holding time is short. The casting wall thickness has drastic changes.
3. The partial tightening force is too large, and the force is uneven when ejected.