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 time is long and even broken.
Lead, tin and cadmium have little solubility in zinc alloys, so they concentrate on the grain boundaries and become cathodes. 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.
The microstructure of the zinc alloy is mainly composed of a zinc-rich solid solution containing Al and Cu and an Al-rich solid solution containing Zn, and their solubility decreases as the temperature decreases. However, since the solidification speed of the die casting 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.
Should not be under high temperature and low temperature
Zinc alloy die castings are not suitable for use in high temperature and low temperature (below 0 °C) working conditions. 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.