Note on the Use of Zinc Alloy
1. Poor corrosion resistance.
When the impurity elements lead, cadmium, and tin in the alloy composition exceed the standard, the casting is aged and deformed, which is characterized by volume expansion, mechanical properties, especially plasticity, and long time and even cracking.
Lead, tin and cadmium have little solubility in zinc alloys and thus concentrate on the grain boundaries to become the cathode. The aluminum-rich solid solution becomes the anode, which promotes intergranular electrochemical corrosion in the presence of water vapor (electrolyte). Die castings age due to intergranular corrosion.
2. Aging effect
The zinc alloy is mainly composed of a zinc-rich solid solution containing Al and Cu and an Al-rich solid solution containing Zn. Their solubility decreases with decreasing temperature. However, since the solidification speed of the die-casting part is extremely fast, the solubility of the solid solution is greatly saturated at room temperature. After a certain period of time, this supersaturation will gradually be removed, and the shape and size of the casting will change slightly.
3. Zinc alloy die castings should not be used in high temperature and low temperature (below 0 °C) working environment. Zinc alloys have good mechanical properties at room temperature. However, the tensile strength at high temperatures and the impact properties at low temperatures are significantly reduced.
4. Zinc alloy die-casting parts may have burrs on the surface due to insufficient clamping force, poor mold clamping, insufficient mold strength, and too high melting temperature. This phenomenon is called product draping, and is often a post-processing process that companies must face. Mainly based on the nature of the product using manual grinding, hydrogen and oxygen explosion and Zhaoling frozen shot blasting machine to solve.