What is the advantage of magnesium alloy die casting parts?
Application of magnesium alloy die casting parts
Magnesium alloy die casting is a systematic project integrating design, manufacturing and research. Compared with those engaged in zinc and aluminum alloy die-casting. Magnesium alloy die-casting workers should have more comprehensive knowledge, experience and research and development capabilities.
Magnesium alloys for automobiles are mainly die-casting products. The use of magnesium die-casting reduces the quality of the car, reduces fuel consumption, and reduces exhaust emissions. In addition, magnesium alloy die castings have the advantages of noise reduction and vibration reduction performance and high casting accuracy. With good overall economic benefits, it is the most promising important material for automobile lightweight and has broad application prospects.
Research on Die Casting Magnesium Alloy
The density of magnesium alloy is less than 2G/CM3, and it is currently the lightest metal structure material. Its specific strength is higher than aluminum alloy and steel, and slightly lower than fiber reinforced plastics with the highest specific strength.
Its specific stiffness is comparable to aluminum alloy and steel, and much higher than fiber reinforced plastics; its corrosion resistance is much better than that of low-carbon steel, and has surpassed die-cast aluminum alloy A380; its vibration damping and magnetic shielding properties are far better than aluminum alloy.
In view of the low dynamic viscosity of magnesium alloy. The filling speed under the same fluid state (Equal Reynolds index) is much higher than that of aluminum alloy. In addition, the melting point, specific heat capacity and latent heat of phase change of magnesium alloy are lower than aluminum alloy. So its melting energy consumption is less. The solidification speed is fast, and the actual die-casting cycle of magnesium alloy can be 50% shorter than that of aluminum alloy. In addition, magnesium alloy has a low affinity for iron and low ability to dissolve iron. So it is not easy to adhere to the mold surface. The life of the mold used is 2 to 3 times longer than that of aluminum alloy.
The commonly used die-cast magnesium alloys are mostly American brands AZ91, AM60, AM50, AM20, AS41 and AE42. Which belong to the four series of MG-AL-ZN, MG-AL-MN, MG-AL-SI and MG-AL-RE respectively. For die-casting magnesium alloys, there are mainly the following researches at present.
High temperature performance
At present, the AZ and AM series of magnesium alloy die castings account for 90% of the magnesium alloy die castings for automobiles. The strength of these two series of magnesium alloys decreases significantly above 150°C.
AS series die-cast magnesium alloys with creep resistance above 150℃ have been developed. For example, AS41A alloy (MG43%AL1%SI0.35%MN), its 175℃ creep strength is better than AZ91D and AM60B. And has higher elongation, yield strength and tensile strength.
Volkswagen’s BEETLE engine crankcase has been using AS41 and AS42 in the past. And an improved alloy AE42 recently used has better creep performance at high temperatures. Certain trace elements, such as rare earth elements Y, ND, SR, etc.. Have obvious grain refinement effects on die-cast magnesium alloys. It can improve the strength and creep resistance of die-cast magnesium alloy.
For example, the recently developed AE42 has better creep resistance than traditional MGALSI alloy. It can be used for a long time at 200-250°C. However, the improvement of AS and AE alloys on high temperature performance is still limited. And its casting performance is worse than that of AZ and AE alloys. In addition, the high cost of rare earth elements makes production and application limited.
Malleability
At present, magnesium die castings are growing very rapidly in applications requiring safety and high fracture toughness. To improve the ability to absorb energy under working conditions, the fracture toughness of the material should be improved. This can be done by reducing aluminum in the alloy.
AM60 and AM50 are widely used in safety components such as dashboard brackets, steering wheel shafts and seats. AM20 is currently also applied to the back frame of the seat. In addition, the relationship between elongation at break and temperature is also quite close, especially when the temperature is above about 50°C, it increases with the increase of temperature.
Corrosion resistance of magnesium alloy
Corrosion resistance has also been a major obstacle to the expansion of magnesium alloys. Magnesium has high chemical activity. Magnesium-based alloys and composite materials are prone to micro-battery corrosion. Generally, low-purity die-cast magnesium alloys have poor corrosion resistance.
High-purity die-cast magnesium alloys (such as AZ91D) with impurity elements such as FE, NI, CU, and AE42 containing rare earths are strictly regulated. The corrosion resistance of its salt spray test has exceeded that of die-cast aluminum alloy A380 and far better than low carbon steel.
Adjustment of chemical composition, surface treatment and control of microstructure can all improve its corrosion resistance. Although there are many ways to improve the corrosion resistance of magnesium alloy parts, if the problem is not solved from the material itself, poor corrosion resistance is always a technical obstacle to the large-scale application of magnesium alloy parts.
Flame retardant magnesium alloy
Adding AL (2.5%), BE alloys (0.0005% to 0.03% of BE) or CA-containing alloys to magnesium alloys can also effectively prevent the oxidation of magnesium alloy liquid.
At present, some researchers are engaged in the research of magnesium alloys with flame-retardant properties. Once this research is successful, magnesium alloys will be melted and cast just like aluminum alloys and will have a wider application prospect.
Magnesium alloy matrix composite
Magnesium alloy-based composite materials reinforced with particles such as silicon carbide have been researched and developed for many years.
Although it has not yet reached the stage of commercial application in the field of die casting, castings such as impellers, bicycle cranks, and automobile cylinder liners have been made by sand casting, precision casting and other methods.
And there is a development trend of combining this composite material with semi-solid casting and applying it in the fields of die casting and squeeze casting.
