Before I start this article, let me introduce myself. I’m Dave from Qingtian Causte Hardware Product Co., Ltd, Our factory produces zinc alloy door locks, iron and aluminum door locks, stainless steel door locks and related door lock accessories，have 17 years of production and sales experience，Equipped with die casting machine, polishing machine, packaging machine, and assembly line. The product sells to the Middle East, Africa, South America and some European countries. It can provide a variety of customized services, including mold development, surface treatment and packaging design.
Zinc alloy is an alloy based on zinc and added with other elements. Commonly added alloying element is aluminum, copper, magnesium, cadmium, lead, titanium, etc. Zinc alloy has a low melting point, good fluidity, easy plastic processing, corrosion resistance in the atmosphere, and easy recycling and remelting of residual waste.；However, the zinc alloy creeps strength is low, and it is prone to natural aging to cause dimensional changes.
1. large specific gravity.
2. Good casting performance can die-cast precision parts with complex shapes and thin walls, smooth casting surface.
3. Surface treatment: electric-plating, spraying, painting, polishing, grinding, etc.
4. Does not absorb iron during melting and die casting, does not corrode and stick.
5. Good mechanical properties and wear resistance at room temperature.
6. Low melting point, melting at 385℃, easy to die casting.
The traditional die-cast zinc alloys are No 2, No 3, No 4, No 5, and No 7. The most widely used is the No. 3 zinc alloy. This article mainly introduces zinc alloys No 2, No 3, and No 5.
Zinc alloy No 2: It is used for mechanical parts that have special requirements on mechanical properties, high hardness requirements, good wear resistance and dimensional accuracy requirements.
Zinc alloy No 3: Good flow and mechanical properties. Used in castings that do not require high mechanical strength, such as Locks, toys, lamps, decorations, and some electrical components.
Zinc alloy No 5: Good fluidity and good mechanical properties. Used in castings with certain mechanical strength requirements, such as auto parts, electromechanical parts, mechanical parts, electrical components.
Which zinc alloy to choose, mainly considering three aspects.
1. The use of the die casting requires and the requirements of the performance
（1） Tensile strength: the maximum resistance when the material breaks；Elongation: the measure of material brittleness and plasticity；hardness: the measure of the resistance to localized plastic deformation.
（2） Working environment status：Operating temperature、humidity、Workpiece contact medium.
（3）Precision requirements：Accuracy and dimensional stability.
（3）Surface treatment process.
3. Economic：The cost of raw materials and the requirements for production equipment（Including smelting equipment, die casting machines, molds etc.），And production costs.
The role of an element in the alloy
In the alloy composition，Effective alloy element：Aluminum、brass、magnesium；Impurity elements：lead、cadmium、tin、iron.
① Improve the casting properties of the alloy，Increase the fluidity of the alloy，Solid solution strengthening，Improve mechanical properties
② Reduce the ability of zinc to react with iron，Reduce erosion of ferrous materials.
Aluminum content is controlled at 3.8 ~ 4.3. Mainly considering the required strength and fluidity，Good fluidity is a necessary condition for obtaining a complete, dimensionally accurate, smooth surface casting.
1. Increase the hardness and strength of the alloy；
2. Improve the wear resistance of the alloy；
1. When the copper content exceeds 1.25%, the size and mechanical strength of the die-casting part change due to aging.；
2. Reduce the extensibility of the alloy.
① Reduce intergranular corrosion
② Refine the alloy structure to increase the strength of the alloy
③ Improve the wear resistance of the alloy
① When the magnesium content is > 0.08%，The toughness and liquidity reduced.
② Easy to oxidize loss in the molten state of the alloy.
4）Impurity elements: Lead, Cadmium, Tin
It makes the intergranular corrosion of zinc alloy very sensitive, accelerates its intergranular corrosion in a warm and humid environment, reduces mechanical properties, and causes dimensional changes of castings.
When the content of lead and cadmium in the zinc alloy is too high, the surface quality is normal when the workpiece is just die-casting, but bubbling appears on the surface after storage for a period of time (eight weeks to several months) at room temperature.
5）Impurity elements: Iron
① Iron reacts with aluminum to form an Al5Fe2 intermetallic compound, causing loss of aluminum and forming scum.
② Forming hard spots in the die casting, affecting subsequent processing and polishing.
③ Increase the brittleness of the alloy.
1. Control alloy composition from the purchase of alloy ingots，Alloy ingots must be based on ultra-high purity zinc，Plus alloy ingots made of ultra-high purity aluminum, magnesium and copper，Supply plants must have strict ingredient standards. High-quality zinc alloy material is a guarantee for the production of high-quality castings.
2. The alloy ingots should be placed in a clean, dry stacking area. Increased slag production by contamination of factory dirt，Also increase metal loss. A clean factory environment is very effective in controlling the composition of the alloy.