Advantages and Disadvantages of Zinc Alloy Die Casting

Zinc alloy die-casting is a method of manufacturing various metal structures using zinc as raw material and die-casting forming method.

Advantages of die-casting parts: Zinc alloy die-casting parts have the characteristics of low density, high strength, corrosion resistance, and easy forming, therefore they have good comprehensive performance. It is also easy to perform mechanical processing in production, and after forming, the surface of the product is smooth. There is no need for waxing, spraying, or painting processes during use. No pollution to the environment. No harmful gases are generated during the casting process. No harm to human body. Due to the low content of alloying elements, a large amount of resources such as lead and zinc can be saved.

Disadvantages of zinc alloy die-casting: Zinc alloy die-casting parts are prone to corrosion and damage due to their high zinc content, and are also prone to casting defects such as cracks, pores, and shrinkage cavities; Alloy elements are easily soluble in zinc solution and remain in the product; During alloy die-casting, defects such as pores are prone to occur due to the influence of impurities, and mold wear is severe due to high temperature, high die-casting speed, long holding time, and high pressure; During zinc alloy die-casting, a large amount of lead needs to be added as an impurity control agent, resulting in high lead content; The cooling speed of die-casting parts is slow, and during the heating process, internal stress is easily generated, leading to defects such as deformation. Therefore, it is required that the forming equipment has sufficient performance and reliability; Die-casting molds and equipment have high investment, high production costs, and long manufacturing cycles.

Currently, it is mainly used in components such as engine blocks, cylinder heads, and wheel hubs for automobiles and motorcycles. Using ordinary die-casting technology can also produce excellent products for other important components such as the crankshaft and connecting rod cap of the engine.

chemical composition

The chemical composition of zinc alloy consists of five parts: ① Zinc, which is the main component of zinc alloy, accounting for approximately 78% of the total weight.

② Carbon is the most important element in alloys, accounting for approximately 5% of the alloy's weight.

③ Silicon, which forms an iron zinc phase with iron, affects the hardness and corrosion resistance of steel.

④ Manganese, which is an important alloying element, has a similar effect to carbon.

⑤ Sulfur, which can prevent oxygen atoms from entering the alloy and causing corrosion.

The chemical composition of zinc alloy is closely related to the die-casting process. In order to obtain die-casting parts with good performance, a zinc content of over 50% is required, and currently, the general die-casting process uses a zinc content between 35% -45%.

Due to zinc being a metal element that is difficult to dissolve in water, in order to avoid defects or damage caused by impurities in die castings, zinc is often co melted with other elements to form alloys.

melting point

For die castings, the melting temperature refers to the lowest temperature at which zinc alloy is melted under heating conditions. For example, below 450 ℃, a low melting temperature (below 300 ℃) will lead to the growth of zinc grains and the precipitation of impurities (such as sulfur, phosphorus, silicon, and rare earth elements), resulting in a decrease in alloy strength.

Although it is advantageous to form zinc alloy under hot deformation temperature during die casting, this is not always the case, as defects such as shrinkage may occur due to casting process reasons. To avoid the occurrence of these defects, appropriate alloy components (including zinc content and other elements) should be selected, and attention should be paid to using the correct die casting process to prevent crystallization and structural changes. Compared to cast iron, zinc alloy has a higher melting point. This means a larger melting point gradient and a smaller tendency for hot cracking, making it more suitable for die-casting formed parts.

Mechanical properties

1) The tensile strength of zinc alloy die castings can reach 400-600 MPa under certain conditions, which is 2-4 times that of cast iron and 2-2.5 times that of aluminum, and several times or tens of times higher than that of cast steel.

2) Zinc alloy die castings have good plasticity, and their plastic deformation ability is 1-2 times that of cast iron. Therefore, it can withstand large loads, and its fatigue strength is about twice that of cast steel. When the temperature is above 700 ℃, the tensile strength can also reach about 100 MPa.

3) Zinc alloy die castings exhibit good thermal stability, thermal contact stability, and thermal conductivity at different temperatures. This is because zinc alloy has a low oxygen content and good oxidation resistance, so the hot deformation temperature can be increased by about 100 ℃ compared to cast iron. In addition, zinc alloys have good chemical stability and corrosion resistance at different temperatures.

Heat resistance

Due to zinc being the most heat-resistant metal, it can be used in environments above 300 ℃. Zinc is the most resistant metal to high-temperature oxidation. In air at 400 ℃ or gas with an oxygen concentration of 0.5%, zinc still has good corrosion resistance and can withstand oxidative corrosion in the atmosphere. But when the temperature exceeds 300 ℃, oxidation corrosion increases rapidly. Therefore, alloying is one of the important ways to improve the heat resistance of zinc alloys.

Electrical performance

Pure zinc is a pure metal zinc with good thermal conductivity but poor conductivity; Copper has a thermal conductivity five times higher than pure zinc, but its conductivity is better.