Common Defects and Solutions in Zinc Alloy Die Casting

Common Defects and Countermeasures in Zinc Alloy Die Casting

Overview

With the continuous advancement of science and manufacturing technology, casting materials have evolved significantly. Among them, zinc alloy die casting has been widely applied in a variety of decorative products. In particular, in the home decoration industry, zinc alloy die castings are highly favored due to their excellent surface quality and superior finishing performance. However, despite these advantages, zinc alloy castings are still prone to certain quality issues during production.

Typical defects in zinc alloy die casting mainly include surface blistering and other visible surface imperfections.

Causes of Defects

1. Porosity-Related Issues

(1) Formation of pores:
During the filling and solidification stages of molten metal, gas entrapment may occur, resulting in pores either on the surface or inside the casting. In some cases, gases released from coating materials may also enter the casting. Additionally, air trapped inside the mold cavity or gases precipitated during alloy solidification can contribute to pore formation. Insufficient mold venting is another key factor leading to porosity defects.

(2) Shrinkage cavities:
As molten metal cools and solidifies, volume contraction naturally occurs. If the remaining liquid metal is insufficient to compensate for this shrinkage, cavities will form. Moreover, uneven wall thickness or localized overheating can slow down solidification in certain areas, further increasing the risk of shrinkage defects and resulting in depressions on the casting surface.

2. Intergranular Corrosion

Zinc alloy materials may contain harmful impurities such as lead, tin, and chromium. These impurities tend to accumulate along grain boundaries, which can trigger intergranular corrosion. As corrosion progresses, the metallic structure weakens and may fracture along grain boundaries. This issue can be further aggravated during electroplating processes. When corrosion spreads, the coating may lose adhesion, eventually leading to surface blistering.

3. Cracking and Flow Defects

Cold shuts and flow marks:
During mold filling, the initially injected molten metal may solidify prematurely. When the later molten metal flows in, it fails to fuse properly with the already solidified portion, creating visible overlapping lines or strip-like marks on the surface. Flow marks are usually shallow, while cold shuts may penetrate deeper into the casting.

Hot cracking:
Hot cracks are often caused by uneven casting thickness, which leads to stress concentration during cooling. Premature ejection before the material gains sufficient strength, uneven external forces during forming, or excessively high mold temperatures can all contribute to grain coarsening and the presence of impurities, ultimately increasing the likelihood of cracking.

Solutions to Defects

To reduce porosity defects, the key approach is to minimize gas entrapment during the casting process. For shrinkage cavities, it is essential to ensure uniform cooling and balanced solidification across all sections of the casting.

To prevent intergranular corrosion, strict control of impurity elements in raw materials is necessary, especially those introduced through recycled or scrap materials. Maintaining material purity significantly improves corrosion resistance.

For flow marks and cold shuts, improving mold temperature control and increasing injection (gate) speed can help enhance metal flow continuity and reduce incomplete fusion defects.

Conclusion

Through proper process control and material management, most common defects in zinc alloy die casting can be effectively reduced or prevented. We hope the above analysis provides useful reference value and helps you better understand defect formation and corresponding solutions.