1, poor corrosion resistance.
When the impurity elements lead, cadmium and tin in the alloy composition exceed the standard, the casting will undergo aging deformation, which shows volume expansion, mechanical properties, especially plasticity, decrease significantly, and even break after a long time.
Lead, tin and cadmium have little solubility in zinc alloys, so they are enriched on grain boundaries to become cathodes, and aluminum-rich solid solutions become anodes, which promote intergranular electrochemical corrosion in the presence of water vapor (electrolyte). Die castings are aged due to intergranular corrosion.
2. Aging effect
The microstructure of zinc alloy is mainly composed of zinc-rich solid solution containing Al and Cu and Al-rich solid solution containing Zn, and their solubility decreases with the decrease of temperature. However, due to the extremely fast solidification speed of die casting, the solubility of solid solution is greatly saturated at room temperature. After a certain period of time, this supersaturated state will gradually ease, and the shape and size of the casting will change slightly.
3. Zinc alloy die castings should not be used at high temperature and low temperature (below 0℃). Zinc alloy has good mechanical properties at room temperature. However, the high-temperature tensile strength and low-temperature impact properties decreased significantly.
4. The surface of zinc alloy die casting will have burrs due to the problems of insufficient clamping force, poor clamping, insufficient mold strength and high melting temperature. This phenomenon is called product edging, which is often a post-treatment process that enterprises must face. According to the nature of the product, it is mainly solved by manual grinding, oxyhydrogen explosion and frozen shot blasting machine.
Zinc alloy is an alloy based on zinc and added with other elements. The alloying elements usually added are low-temperature zinc alloys, such as aluminum, copper, magnesium, cadmium, lead and titanium. Zinc alloy has low melting point, good fluidity, easy welding, brazing and plastic processing, corrosion resistance in the atmosphere, and easy recycling and remelting of waste materials; However, the creep strength is low, and it is easy to change dimensions due to natural aging. Prepared by melting, die casting or press working. According to the manufacturing process, it can be divided into cast zinc alloy and deformed zinc alloy. The main additive elements of zinc alloy are aluminum, copper and magnesium. Zinc alloy can be divided into deformed zinc alloy and cast zinc alloy according to processing technology. The cast zinc alloy has good fluidity and corrosion resistance, and is suitable for die-casting instruments, automobile parts shells and so on.