Modern metal pressure die casting is the process of rapid development of a high-efficiency, low non-cutting metal forming precision casting method, which has been widely used in various industries of the national economy; and also due to the different needs of the industry, for die-casting metal materials have different requirements and options.
In the choice of die-cast material, it should be based on a variety of factors product performance, process performance, production conditions, economy and the characteristics of die-cast materials, etc., selecting the correct casting material.
Common casting materials include aluminum, zinc alloys and magnesium alloys.
Aluminum die-casting is the most widely used material, widely used in automotive, motorcycle industry, aviation and aerospace. Aluminum following features:
Density 1) aluminum is small, only about iron, copper, zinc 1/3, specific strength and stiffness is its advantage.
2) an aluminum alloy having good electrical conductivity, thermal conductivity.
3) Aluminum antioxidant good corrosion. In the air, the surface of the aluminum oxide disulfide easily formed a dense oxide film, can prevent further oxidation.
4) The aluminum alloy casting having excellent properties. Aluminum die-casting process is simple, forming and cutting performance is good, with high mechanical properties and corrosion resistance, is the most potential to replace steel casting alloy.
5) good high temperature mechanical properties of aluminum alloy, the same good mechanical properties while working at low temperatures.
6) Disadvantages aluminum alloy is prone to large centralized solidification shrinkage in the last place. In addition, aluminum and iron has a strong affinity, easy to stick mold should be pressed against the cold chamber die casting machine.
Magnesium alloy, magnesium alloy characteristics are as follows:
1) Magnesium alloy is called "green engineering material of the 21st century", the density of aluminum 2/3, 1/4 of steel, but the specific strength and specific stiffness are superior to aluminum and steel, much higher than the engineering plastics, is a good, lightweight structural materials.
2) Magnesium alloy has good energy absorption and vibration absorption properties for housing can reduce noise transfer product for moving parts can absorb vibration, to extend the life of parts.
3) has a good electromagnetic shielding, electromagnetic radiation can provide electronic products.
4) rigidity and impact resistance.
5) scalability, easy to shape, to make the product design flexibility, improve product quality.
6) Magnesium alloy low melting point, making the low deformation, high dimensional accuracy, is conducive to forming a mold; low affinity with iron, sticking to the mold of small, help to improve productivity and tool life; and good magnesium alloy flow properties conducive to complex parts and small pieces of the production.
7) The best machining performance, the required cutting force, good cutting performance, long tool life.
8) good heat dissipation, second only to aluminum.
9) good dimensional stability, ambient temperature and time change little effect on the size.
10) can be 100% recycled.
11) Magnesium alloy is easily oxidized in air, it is necessary after the forming of magnesium alloy die castings surface treatment to improve corrosion resistance, improved part surface quality. Common surface treatment methods include electroplating, painting, anodic oxidation. Similarly magnesium alloy high temperature brittleness, thermal cracking tendency big disadvantage.
Zinc is also more common characteristics of zinc alloy is as follows:
1) zinc alloy with excellent casting properties, mechanical properties, toughness, in traditional mechanical parts, hardware, locks, toys and other industrial applications is very broad.
2) zinc alloy with excellent electrical and thermal conductivity, good vibration damping characteristics, good electromagnetic shielding performance 'applications continue to grow on electronics, telecommunications, household electrical appliances.
3) zinc alloy is a versatile, reliable, low-cost materials and easy casting production. Die-cast zinc alloy has good performance, making it easier to die-casting complex shape, thin-walled, high dimensional accuracy of the product. Since the thin-wall casting characteristics of the zinc alloy products can achieve weight reduction and cost reduction requirements.
4) Compared with aluminum and magnesium alloys, zinc alloys with high tensile strength, yield strength, impact toughness and hardness, good elongation.
5) zinc alloy die casting surface is very smooth, surface treatment may be used directly, but also more susceptible to various surface treatments such as polishing, plating, painting, etc., in order to obtain a better surface quality.
6) Zinc alloy low melting point, melting at 385 ℃, compared to aluminum and magnesium alloy, zinc alloy die casting easiest.
7) The poor corrosion resistance. When the zinc alloy composition of impurity elements such as lead, cadmium, tin than the standard time will deform gradually aging, expressed as a volume swell, mechanical properties (especially plastic) decreased significantly, a long time will break.
8) timeliness. Used for too long, zinc alloy die casting shapes and sizes may vary slightly.
9) Zinc alloy should not be used at high temperature and low temperature environment. Zinc alloy with good mechanical properties at room temperature, but at a high temperature impact properties were significantly decreased under tensile strength and low temperatures. Zinc alloy easy to aging, which is the main reason for the scope of application of the zinc alloy is limited. Zinc alloy operating temperature range is narrow, the temperature is below 10 ℃, the impact toughness decreased rapidly at elevated temperatures, mechanical performance, and easy to creep, so that the temperature and the force components is generally not exceed lOOC . Strict control of purity and zinc smelting process Yi Yi alloy material, add a small amount of Mg and the amount of Cu in zinc alloy, can reduce or eliminate aging and to improve cutting performance.
To sum up the characteristics of casting material analysis, combined with the article "requirements of aluminum die casting raw materials," Fu-wah metal casting plant above analysis, the analysis results good molding die castings for the material to be processed there are certain requirements, and each of the different metal processing materials, components between them is certainly not the same, you can refer to the article "Zinc alloy die casting components."
So each of the three components of die-casting machine materials are different, but the composition of the various elements in the die casting process are taken into effect with various metallic element related to, let's be more specific analysis, the die casting material the role of various metal elements.
[1]. Silicon (Si) Silicon is the main element most die-cast aluminum alloy, it can improve the performance of the alloy casting, general content of 7-11%. Silicon Role:
1, to improve liquidity superalloy
2, to reduce shrinkage
3, to reduce the tendency of hot cracking
4, to improve the wear resistance
But more than 12% silicon, silicon and aluminum had eutectic, while copper, iron and other impurities in addition, that the emergence of hard particles of free silicon, so machining difficult, high silicon aluminum alloy castings crucible ablation serious role.
[2]. Copper (Cu)
The copper content of the alloy is usually 2.5% to 5% increase in copper content, to improve liquidity, tensile strength and hardness of the alloy, but reduces the corrosion resistance and ductility, thermal tends to increase.
[3] Magnesium (Mg)
Adding a small amount (about 0.2 to 0.3%) of magnesium in high silicon aluminum alloy, it can improve the strength and yield strength, improve the alloy machinability.
Magnesium content is too high, casting performance deteriorated at a high temperature strength and ductility are low, large shrinkage upon cooling, it is easy to produce thermal cracking and the formation of osteoporosis.
[4] zinc (Zn)
Zinc aluminum zinc aluminum can improve the liquidity, improve casting performance, improve the tensile strength, but tends to increase hot cracking, corrosion resistance decreases, generally less than 1.2%.
[5] iron (Fe)
Since aluminum adhesion of mold is very strong, when the iron content of 0.6% or less is particularly strong. When more than 0.6%, the sticky mold phenomenon will be greatly reduced, so that the iron content should be controlled within a range of 0.6 to 1% of the die-casting is good.
When the iron content is too high, iron with FeAl3, Fe2Al7 and flake or needle organization Al-Si-Fe is present in the alloy, reducing mechanical properties, such organizations will reduce the flow of the alloy, thermal resistance increases large, corrosion resistance decreases.
[6]. Manganese (Mn)
Manganese in the aluminum alloy can reduce the harmful effects of iron, can flake or needle tissue formed by the iron in aluminum alloys into fine crystal structure, it is generally aluminum allow the presence of 0.5% or less of manganese. When the manganese content is too high, it will cause segregation, the general control of the manganese content of 0.6% or less.
[7] nickel (Ni)
Nickel aluminum can improve the strength and hardness of the alloy, reduce corrosion resistance. Like the role of nickel and iron, can reduce the mold corroded alloy, while the harmful effects of iron improve the welding properties of the alloy. When the nickel content of 1 to 1.5%, the casting has been polished smooth surface can be obtained. Due to the lack of sources of nickel, aluminum alloy containing nickel should be minimal.