1, poor corrosion resistance
When the impurities in alloy composition lead, cadmium and tin exceed the standard, they lead to the aging of the casting and deformation, which is characterized by volume swelling, mechanical properties, especially plasticity decreased significantly, and even a long time rupture. The solubility of lead, tin, cadmium in zinc alloy is very small, so focus on the grain boundary and become the cathode aluminum rich solid solution as the anode. In water vapor (electrolytes) under the conditions of existence, to intergranular corrosion. Die castings are aged because of intergranular corrosion.
2, aging effect
The microstructure of zinc alloy is mainly composed of zinc rich solid solution containing Al and Cu and rich Al solid solution containing Zn. Their solubility decreases with the decrease of temperature. However, the solidification rate of the die castings is so high that the solubility of the solid solution is greatly saturated at room temperature. After a certain period of time, this phenomenon of supersaturation will gradually be relieved, and the shape and size of the casting will change slightly.
3, should not be in high temperature and low temperature
Zinc alloy die castings should not be used in high or low temperature (under 0) working environment. Zinc alloy has good mechanical properties at room temperature. But under high temperature, tensile strength and impact properties at low temperature decreased significantly