Aluminum alloy is heavier than magnesium. Due to its excellent high corrosion resistance and good smooth appearance, aluminum alloy can be used to obtain good mechanical and physical properties. Magnesium alloy die castings can cast thin-walled and complex products. Zinc die castings have good casting performance and can cast complex, thin wall, high precision and smooth surface shapes and parts. Zinc is the heaviest substance, so it is recommended to cast a small part. Zinc has good surface treatment ability. It has a smooth surface through electroplating, spraying and painting.
1、 Aluminum die castingAluminum alloy: the main alloy elements are copper, silicon, magnesium, zinc, manganese, and secondary alloy elements such as nickel, iron, titanium, chromium, lithium, etc.
Classification of aluminum alloysAluminum alloys are divided into two categories: cast aluminum alloys, which are used in the cast state; Deformed aluminum alloy can withstand pressure processing, and its mechanical properties are better than those in casting state. Aluminum alloy materials can be processed into various shapes and specifications. It is mainly used for manufacturing aviation equipment, daily necessities, building doors and windows, etc.
Processing method of aluminum alloyAluminum alloy can be divided into deformed aluminum alloy and cast aluminum alloy. Cast aluminum alloy can be divided into non heat treated aluminum alloy and heat treated aluminum alloy. The mechanical properties enhanced by non heat treatment can not be improved by heat treatment, but can only be strengthened by cold working deformation. It mainly includes high-purity aluminum, industrial high-purity aluminum, industrial pure aluminum and antirust aluminum. Aluminum alloys can improve mechanical properties through quenching and aging heat treatment. They can be divided into hard aluminum, forged aluminum, aluminum and special aluminum alloys.
2、 Magnesium die casting
magnesiumMagnesium has low density and easy combustion, which depends on its physical and chemical properties. At 20 degrees, the density of metallic magnesium is 1.738 g / cm3 and the density of liquid metallic magnesium is 1.58 g / cm3. At standard atmospheric pressure, the melting point of magnesium metal is (650 + 1) and the boiling point is 1090. When heated in air, the combustion temperature of magnesium is 632 ° C to 635 ° C. Therefore, the preparation of magnesium and the melting process of its alloy are more complex. The purity of industrial magnesium can reach 99.9%, but it can not be used as pure magnesium, aluminum and zinc, lithium, manganese, zirconium and rare earth elements. Magnesium alloys are formed from high-strength pure magnesium. At present, magnesium alloys are the most widely used, followed by magnesium manganese alloys and mg Zn Zr alloys. It is mainly used in aviation, aerospace, transportation, chemical industry, rocket and other industrial departments.
Properties of magnesium alloysLight weightThe proportion of magnesium is only 1.8g/cm3, the proportion of aluminum alloy is 2.7g/cm3, the weight of magnesium alloy is 30% lighter than aluminum alloy, and the weight of steel is 80% lighter than steel. Therefore, magnesium alloy has become an ideal material for parts manufacturing in automobile and portable electronic products.
strengthMagnesium alloys in metal and plastic engineering materials have excellent strength / weight ratio. The yield strength is 160MPa and the tensile strength is 240mpa.
Die casting performanceUnder the condition of maintaining good structure, the minimum wall thickness of magnesium alloy is allowed to reach 0.6mm, which cannot be achieved with the same strength. The die casting performance of aluminum alloy is greater than 1.2-1.5mm, which can be compared with magnesium alloy. Magnesium alloy is easy to die cast and suitable for mass production (the production speed can reach 1.5 times that of aluminum). In addition, the wear of magnesium alloy die is lower than that of aluminum alloy, mainly due to the high viscosity of aluminum.
Damping performanceShockproof magnesium alloy has excellent damping performance, can absorb vibration and noise, and can be used as equipment shell to reduce noise transmission, prevent vibration and prevent damage to depression. As LCD or LED is a good choice.
rigidityMagnesium is twice as rigid as aluminum and is higher than most plastics. Magnesium has good stress resistance.
High EMI shieldingMagnesium alloy has good electromagnetic wave blocking function and is suitable for the production of electronic products.
Good cutting performanceMagnesium has better machinability than aluminum and zinc, making it more likely to cut metal materials.
Advantages of magnesium alloy materials and magnesium die castingLight weightThe proportion of magnesium alloy in all structures is light, accounting for 68% of aluminum alloy and 27% and 23% of zinc alloy steel. In addition, its 3C product shell and internal structure are also excellent materials for automobile, aircraft and other parts.
Strength and stiffnessThe specific strength of magnesium alloy is significantly higher than that of aluminum alloy and steel, and the stiffness ratio is equal to that of aluminum alloy and steel, which is much higher than that of engineering plastics. It is 10 times that of ordinary plastic.
Good vibration resistanceUnder the same load, the damping capacity is 100 times that of aluminum and 300 to 500 times that of titanium alloy.Good electromagnetic shielding performanceThe shell of 3C products (mobile phones and computers) can provide excellent electromagnetic protection, while the magnesium alloy shell can absorb more than 100dB electromagnetic interference frequency.
Good heat dissipationGenerally, the thermal conductivity of metal is hundreds of times. The thermal conductivity of magnesium alloy is slightly lower than that of aluminum alloy and copper alloy, while the thermal conductivity of aluminum alloy and copper alloy is much higher than that of titanium alloy, and the heat is close to water.
Stability of resource supplyThe reserves of magnesium in the earth’s crust rank eighth. Most of the raw materials come from marine refining, so it is stable and full of resources.
Defects of magnesium alloy die castingDue to the extremely high filling speed and curing speed, it is easy to produce the holes involved, which is very important for the treatment of rubber, waste gas and cold air. The casting cannot be too thick, and the wall thickness can only be limited to a certain size. Cheap die-casting alloy has limited mechanical properties. The mobile phone industry restricts the use of die-casting alloy AZ91D castings, which have poor creep resistance due to small grains. The poorly cast mg Al RE magnesium alloy is creep resistant 6 and expensive. It cannot be heat treated, is not suitable for welding, and requires the use of shielding gas.
Zinc die casting4-1 ZnAl is commonly used as electroplated zinc base alloy material of this brand, with composition (%): Al 3.5 ~ 4.9, Cu 0.75 ~ 1.25, Mg 0.03 ~ 0.08, and the balance is Zn. The ratio is significant, and surface treatment can be carried out: electroplating, spraying, painting, melting and casting, no iron absorption, no corrosion, pressure type, no die sticking. It has good mechanical properties and wear resistance, low melting point, melting point 385 ℃, easy to cast.
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