Common Defects and Solutions in Zinc Alloy Die Casting

Overview

• With the development of science and technology, the materials used in castings have undergone significant changes, and zinc alloy die casting has been widely used in various decorative applications. Especially in home decoration, zinc alloy die castings have always been popular due to their high-quality surface and excellent surface treatment properties. However, zinc alloy castings also have some defects.

• Common defects in zinc alloy die casting include raised bubbles and surface defects.

Reasons for Defects

1. Caused by pores
(1) Causes of porosity: During the filling and solidification process of the molten metal, gas intrusion can cause pores on the surface or inside the casting. Or, gases emitted from the coating can intrude, leading to the formation of pores. In addition, the gases that form pores also include: gases in the mold cavity, gases precipitated during alloy solidification, etc. Poor mold venting will lead to the formation of pores.
(2) Causes of shrinkage cavities: During the solidification process of the molten metal, due to the volume shrinkage of the metal liquid, the solidified part does not receive sufficient molten metal, resulting in shrinkage cavities. Uneven thickness of the casting or local overheating of the casting leads to slow solidification, and the volume shrinkage forms a concave position.
2. Intergranular corrosion
Zinc alloy components contain a large number of harmful impurities, such as lead, chromium, tin, etc., which will accumulate at the grain boundaries, leading to intergranular corrosion. The metal matrix will fracture due to intergranular corrosion, and electroplating will aggravate the damage. After the intergranular corrosion area expands, the coating will lift, causing blistering on the casting surface.
3. Causing cracks
Water lines and cold lines: During the filling process, the molten metal that enters first will solidify prematurely, and the molten metal that enters later will merge with the solidified molten metal, forming overlapping lines and strip-shaped defects at the joint on the casting surface. Water lines are generally shallow on the casting surface, but cold lines can penetrate deeper. Hot cracking: When the casting thickness is uneven, stress is generated during the solidification process; premature ejection occurs when the metal strength is insufficient; uneven stress is applied to the top; excessively high mold temperature leads to coarse grains or the presence of harmful impurities.

Solutions to Defects

Methods to solve defects in zinc alloy die casting:
The key to controlling porosity is to reduce the amount of gas mixed into the casting. For shrinkage cavities, it is necessary to ensure uniform heat dissipation and simultaneous solidification in all parts of the die casting solidification process. For intergranular corrosion, the main focus is on controlling the content of harmful impurities in the alloy raw materials and paying attention to the impurity elements brought in by scrap materials. For flow lines and cold shuts, the mold temperature can be increased and the gate speed can be increased to reduce the occurrence of cold shuts.
We believe that you should now have a better understanding after reading the above information. We hope it will be helpful to you.