Common Material for Die Casting and Common Problem

When choosing die-casting materials, mechanical engineers should reasonably select the correct die-casting materials according to the factors such as function performance, process performance, production conditions, economy and characteristics of die-casting materials. Commonly used die-casting materials for mechanical parts include aluminium alloy, zinc alloy and magnesium alloy.

Aluminum alloy is the most widely used die-casting material, which is widely used in automobile industry, motorcycle industry, aerospace industry and so on.

The characteristics of aluminium alloys are as follows:

(1) The density of aluminium alloy is small, only about 1/3 of that of iron, copper and zinc. Its outstanding advantages are high specific strength and stiffness.

(2) Aluminum alloy has good conductivity and thermal conductivity.

(3) Aluminum alloy has good corrosion resistance. In air, a dense sulfur trioxide oxide film is easily formed on the surface of aluminium, which can prevent further oxidation.

(4) Aluminum alloy has good die casting properties. Aluminum alloy is the most potential alloy to replace iron and steel castings because of its simple process, good forming and cutting properties, high mechanical properties and corrosion resistance.

(5) The mechanical properties of aluminium alloy at high temperature are good, and it also keeps good mechanical properties at low temperature.

(6) The disadvantage of aluminium alloy is that it is easy to produce large concentrated shrinkage at the final solidification point. In addition, aluminium alloy has a strong affinity with iron and is easy to stick to the die. It should be pressed on the cold chamber die casting machine.

Zinc alloys are also common. The characteristics of zinc alloys are as follows:

(1) Zinc alloys have excellent casting properties, mechanical properties and toughness, and are widely used in traditional mechanical parts, hardware, locks, toys and other industries.

(2) Zinc alloys have excellent electrical and thermal conductivity, good vibration damping properties, and good electromagnetic shielding properties. Their applications in electronics, telecommunications and household appliances are increasing.

(3) Zinc alloy is a universal, reliable and low-cost material, which is easy to be produced by die casting. Zinc alloy has good die-casting performance, so it is easier to die-cast products with complex shape, thin wall and high dimensional accuracy. Because of the thin-wall casting property of zinc alloy, the requirement of lightweight product and low cost can be realized.

(4) Compared with aluminium alloy and magnesium alloy, zinc alloy has higher tensile strength, yield strength, impact toughness and hardness, and better elongation.

(5) The surface of zinc alloy die castings is very smooth, which can not be used directly without surface treatment. At the same time, it is easier to carry out various surface treatments, such as polishing, electroplating, spraying and so on, in order to obtain better surface quality.

(6) Zinc alloy has low melting point and melts at 385 (?) C. Compared with aluminium alloy and magnesium alloy, zinc alloy is the easiest to die-cast.

(7) poor corrosion resistance. When the impurity elements such as lead, cadmium and tin in zinc alloy exceed the standard, they will gradually age and deform, which is characterized by volume expansion, significant decrease in mechanical properties (especially plasticity), and rupture over a long period of time.

(8) timeliness. The shape and size of zinc alloy die castings will change slightly if the service time is too long.

(9) Zinc alloy should not be used in high temperature and low temperature working environment. Zinc alloy has good mechanical properties at room temperature, but its tensile strength at high temperature and impact properties at low temperature are significantly reduced. Zinc alloys are easy to aging, which is the main reason that the application range of zinc alloys is limited. The impact toughness of zinc alloy decreases sharply when the temperature is lower than 10 C. When the temperature rises, the mechanical properties of zinc alloy decrease and creep easily occurs. Therefore, the temperature of the parts under stress generally does not exceed lOOC. Strictly controlling the purity of zinc alloy raw materials and smelting process, adding a small amount of Mg and appropriate amount of Cu in zinc alloy can reduce or eliminate aging phenomenon and improve cutting performance.

Another is magnesium alloy, which has the following characteristics:

(1) Magnesium alloys are known as "green engineering materials in the 21st century". Their density is 2/3 of aluminium alloys and 1/4 of iron and steel, but their specific strength and stiffness are superior to those of aluminium alloys and steel, far higher than engineering plastics. Magnesium alloys are excellent and lightweight structural materials.

(2) Magnesium alloy has good energy absorption and vibration absorption characteristics. It can reduce noise transmission when used in product shell, absorb vibration for moving parts and prolong service life of parts.

(3) It has good electromagnetic shielding and can provide electromagnetic radiation protection for electronic products.

(4) Good rigidity and impact resistance.

(5) It has good ductility and is easy to form. It can make product design flexible and improve product grade.

(6) Magnesium alloys have low melting point, which makes low temperature deformation small, high dimensional accuracy, and is conducive to one-time open-die forming; small affinity with iron, small adhesion phenomenon to dies, which is conducive to improving productivity and die life; and good fluidity of magnesium alloys is conducive to the production of complex parts and small parts.

(7) The mechanical processing performance is the best, the cutting force required is small, the cutting effect is good, and the tool life is long.

(8) Good heat dissipation, second only to aluminium alloy.

(9) The size stability is good, and the influence of environmental temperature and time on the size is small.

(10) 100% regeneration.

(11) Magnesium alloys are easy to oxidize in air. After forming, magnesium alloy die castings must undergo surface treatment to improve corrosion resistance and surface quality of parts. Common surface treatment methods include electroplating, spraying, anodizing, etc. Similarly, magnesium alloys have the disadvantages of high temperature brittleness and hot cracking tendency.

Common problems and solutions:

1. [Hammer stuck]

In order to avoid hammer sticking, we can start from two aspects: 1. In production, we often measure temperature to avoid hammer sticking caused by too high temperature of hammer head and barrel; 2. In the use of materials, we should select high-quality alloy materials to avoid impurity infiltration and put them back into the material.