Cast magnesium alloy

1.1 Die castingZLSYoYike manufacturer company

Die casting is the most important and most widely used forming process for magnesium alloys. Magnesium alloy has excellent die casting process performance: magnesium alloy liquid has low viscosity, good fluidity, and is easy to fill complex cavities. Die castings with a wall thickness of 1.0mm to 2.0mm can be easily produced with magnesium alloys, and now the minimum wall thickness can reach 0.6mm. The casting slope of magnesium die castings is 1.5, while that of aluminum alloys is 2 to 3 degrees. The dimensional accuracy of magnesium die castings is 50% higher than that of aluminum die castings. The melting point and latent heat of crystallization of magnesium alloys are lower than those of aluminum alloys. During the die-casting process, the erosion of the mold is smaller than that of aluminum alloys, and it is not easy to stick to the mold.ZLSYoYike manufacturer company
ZLSYoYike manufacturer company
The life of the mold can be 2-4 times longer than that of aluminum alloys. The die casting cycle of magnesium alloy parts is shorter than that of aluminum parts, so the production efficiency can be increased by 25% compared with aluminum alloy parts. The processing performance of magnesium alloy castings is better than that of aluminum alloy castings. The cutting speed of magnesium alloy parts can be increased by 50% compared with aluminum alloy parts, and the processing energy consumption is 50% lower than that of aluminum alloy parts. Production experience shows that due to high production efficiency, the total cost of small parts of magnesium alloys by hot chamber die casting is lower than that of aluminum alloys by cold chamber die casting.ZLSYoYike manufacturer company

Die-casting magnesium alloys can be divided into four series according to their composition: AZ (MgZLSYoYike manufacturer company

-AL-Zn) series (AZ91), AM (Mg-AL-Mn) series (AM60, AM50), AS (Mg-A1-Si series (AS41,ZLSYoYike manufacturer company

AS21), AE (Mg-AL-RE) series (AEA2).ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

AZ series alloy AZ91 has good casting properties and the highest yield strength, and its die castings are widely used in various forms of parts such as car seats and gearbox casings. AM series alloys AM50 and AM60 have high elongation and toughness, and are used in occasions with high impact load resistance and high safety, such as wheels and doors. AS series magnesium alloys AS41, AS21 and AE series AFA2 are heat-resistant die-cast magnesium alloys developed in the 1970s.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

Cold and hot chamber die casting methods are widely used in magnesium alloy die casting. Generally, hot chamber die casting machines are used for thin-walled castings, and cold chamber die casting machines are used for thick-walled castings. Magnesium alloy hot-chamber die-casting machine is currently the most widely used magnesium alloy die-casting special equipment in foreign countries. The main disadvantage is the high cost of equipment and maintenance.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

During magnesium alloy die-casting, the high-speed turbulent movement of the alloy liquid when filling the die prevents the gas in the cavity from being discharged, which will lead to loose tissue and even bulge or deformation on the surface of the casting. Die casting process parameters such as pressure, speed, melt temperature, mold temperature, etc. have a significant impact on casting properties. Many new die-casting methods, including vacuum die-casting, oxygen-charged die-casting and squeeze casting, overcome the above shortcomings to a certain extent, reduce defects such as porosity and pores of castings, and improve the density of castings. C. Rozak, a precision forming company in Ohio, USA, introduced the metal compression forming technology (MCF) of magnesium alloys. The molding method of pressing the entire surface of the casting, solidifying under pressure, improving the microstructure, reducing the grain size and porosity, The castings are dense and uniform, and can be used to produce castings with high performance requirements and complex shapes.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

1.2 Investment castingZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

Investment casting is one of the more advanced casting technologies in the world. In principle, investment casting is suitable for the preparation of small-volume and high-precision castings. It is currently used to produce aluminum alloys and even nickel-based superalloys. In the development process of magnesium alloy castings, some workpieces have complex structures, some parts have very thin wall thicknesses, and have strict requirements on surface roughness and dimensional tolerances, so investment casting can be used to produce them.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

When using investment casting to produce castings, it has the characteristics of no mold taking, no core and no parting surface, so the dimensional accuracy and surface roughness of the castings are close to investment castings. In addition, investment casting provides a sufficient degree of freedom for the structural design of castings. Originally, components assembled from multiple parts can be integrally poured by bonding them into one piece after molding, so many complex parts can be produced economically. ZLSYoYike manufacturer company
ZLSYoYike manufacturer company
However, investment casting equipment investment and unit casting cost are high, and the workpiece size is limited. In addition, there is a highly reactive reaction between magnesium and oxide ceramics for investment casting materials and bonding materials, which greatly limits its application. When producing magnesium alloy thin-walled parts, it is necessary to preheat the mold in order to fill the thin-walled parts. However, the preheating temperature and pouring temperature are too high to promote the reaction between the magnesium alloy and the mold. Studies have shown that ZrO2 is a promising casting material when using a low mold preheating temperature.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

1.3 Lost Foam CastingZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

Lost foam casting is a new type of casting technology with nearly no allowance and accurate forming. It has many advantages. For example, the molding sand does not need binders, the casting shakeout and sand treatment systems are very simple, and it is easy to achieve clean production; castings are not divided into parts. The profile and the draft angle can make the structure of the casting high; the processing and assembly time can be reduced, and the cost of the casting can be reduced by 10%-30%, etc.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

Preliminary experimental research shows that the characteristics of magnesium alloys are very suitable for the lost foam casting process, because the lost foam casting of magnesium alloys has the following unique advantages in addition to the above characteristics:ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

①At the pouring temperature of magnesium alloys, the decomposition products of foam patterns are mainly aerosol substances such as hydrocarbons, benzenes and styrene, which have a natural protective effect on liquid magnesium alloys that are easily oxidized during punch forming;ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

②The use of dry sand negative pressure molding avoids the contact between the magnesium alloy liquid and the moisture in the molding sand and the casting defects caused by it;ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

③Compared with the currently commonly used magnesium alloy die-casting process, its investment cost is greatly reduced, and the good concession of dry sand reduces the tendency of hot cracking during solidification and shrinkage of magnesium alloy; the slow and stable filling speed of molten metal avoids The entrainment of gas enables the casting to further improve its mechanical properties by heat treatment. Therefore, the lost foam casting of magnesium alloys has great application prospects.ZLSYoYike manufacturer company
 ZLSYoYike manufacturer company

The characteristics of solidification and chemical properties of magnesium alloys make magnesium alloys have many problems in lost foam casting, especially insufficient pouring and oxidative combustion. Due to the low density and specific heat capacity of magnesium alloys, the heat required to vaporize the foam pattern comes from the latent heat of the high-temperature liquid magnesium alloy, which hinders the filling, and the crystallization temperature range of the magnesium alloy is wide, so the pressure head of the molten metal during the lost mold filling The effect is small, and it is easy to stop the flow prematurely, resulting in insufficient pouring defects. The chemical reaction of magnesium alloys may be controlled by the use of flame retardants used in the magnesium alloy sand casting industry and the auxiliary use of pattern coatings with high porosity.ZLSYoYike manufacturer company
ZLSYoYike manufacturer company
Controlled atmospheres can also be used to prevent oxidative combustion during casting. In addition, the high-density foam pattern absorbs more heat, produces more liquid and gaseous products, and reduces the fillability of magnesium alloys. However, the reducing atmosphere generated by the foam pattern during the pouring process reduces or even prevents the oxidative combustion of the magnesium alloy, which ensures the safety of the magnesium alloy during the processing and forming process, and is also conducive to ensuring the cleanliness and quality of the magnesium alloy melt.ZLSYoYike manufacturer company