Semi-solid magnesium alloy continuous casting and rolling technology

This article introduces the basic features and benefits of magnesium alloy, focuses on the semi-solid processing technology, continuous casting and rolling technology, semi-solid magnesium alloy continuous casting technology and its future prospects, pointing out its processing technology will be further developed.

Magnesium alloy is the lightest metal structural material currently used. It has low density, high specific strength and specific stiffness, excellent electrical and thermal conductivity, good dimensional stability and good electromagnetic shielding. It is used in aviation and automobile transportation industry, computer and communication. The industry has developed rapidly. China is a large country of magnesium resources, but at present China's magnesium alloy production scale is still relatively small, production technology is still immature, we should seize this rare opportunity to bring China's magnesium alloy production level to a new height.

First, the basic properties of magnesium alloy

(1) Physical and mechanical properties of magnesium alloys

The physical and mechanical properties of magnesium alloys and other related materials are shown in the table below.

Comparison of physical and mechanical properties of magnesium alloys and related materials

It can be seen from Table 1 that the main mechanical properties of magnesium alloy are close to that of aluminum alloy, but its density is less than that of aluminum alloy, and the specific strength is 1.8 times that of aluminum alloy. It can be said that magnesium alloy has the highest specific strength in the applied metal range. . Compared with engineering plastics, the density of magnesium alloy is higher than that of it, but its melting point is 4-6 times, its specific strength is about 1.8 times. In addition, the thermal conductivity of magnesium alloy is more than 300 times that of engineering plastics. , has obvious advantages in the application of some electronic products.

(2) Advantages of magnesium alloy products

1. Light weight: density is about 1.8g/cm ³ , which is l/4 of iron, 2/3 of aluminum, similar to plastic; 2. high specific strength, good rigidity, better than steel and aluminum; 3. vibration/ High impact absorption, excellent shock resistance, good impact and wear resistance; 4, excellent thermal conductivity, improve heat dissipation of electronic products; 5, non-magnetic metal, anti-electromagnetic interference, good electromagnetic shielding; Good processing and forming performance, beautiful appearance and good texture; 7. Material can be 100% recycled, high recovery rate, Futai environmental protection method; 8. Good creep resistance, dimensional stability, small shrinkage, not easy to be affected by time and environment Temperature changes (relative to plastic).

Second, semi-solid magnesium combined continuous casting and rolling technology

(1) Semi-solid processing technology

Semi-solid processing is a process in which a metal material is subjected to a semi-solid temperature interval during a transition from a solid state to a liquid state or a liquid state to a solid state. Semi-solid technology combines the advantages of liquid casting and solid-state pressure processing. Semi-solid processing technology can greatly improve the mechanical properties of materials and save materials. It is one of the hottest research hotspots in the field of materials. Semi-solid molding technology is an efficient and high-quality molding method that has emerged in recent years.

The main forming methods for semi-solid processing are die casting and forging. In addition, some methods such as extrusion and rolling have been tested. The process route has two routes: one is to maintain the semi-solid temperature of the semi-solid slurry obtained by stirring. Direct forming directly, commonly referred to as rheocasting; the other is to prepare a semi-solid slurry into a billet that is cut according to product size and then reheated to a semi-solid temperature forming, commonly referred to as thixoforming. For the thixoforming, since the semi-solid billet is easy to convey and form and easy to automate, it has been widely used in the industry earlier. For rheocasting, since the semi-solid slurry after stirring is directly formed, it has the characteristics of high efficiency, energy saving, and short flow, and has developed rapidly in recent years.

In the semi-solid metal forming process, since the non-dendritic semi-solid slurry is used, the almost uniform spherical fine-grain structure can be directly obtained, and the structural properties of the metal material are remarkably improved. The surface of the semi-solid forming part is smooth and smooth, the grain is fine, and the mechanical property is good; the latent heat of partial solidification of the semi-solid slurry has been released, so on the one hand, the heat effect on the processing equipment is small, the selection range of equipment materials is expanded, and the manufacturing equipment is difficult. On the other hand, the semi-solid slurry itself has a small solidification shrinkage and an accurate product size. It can be seen that semi-solid processing technology has great advantages over traditional processing technology. At present, more and more scientific and technological workers attach great importance to semi-solid processing technology, and have carried out extensive research in process experiments and theory.

(2) Continuous casting and rolling technology

The continuous casting and rolling technology directly injects molten metal between two oppositely rotating casting rolls to solidify under the cooling and rolling action of the casting rolls and has a certain amount of rolling deformation, thereby directly obtaining a metal strip blank. A near-final forming process.

The continuous casting and rolling process is a molding process that combines rapid solidification and hot rolling deformation. In this process, the casting rolls serve the dual functions of "crystallizer" and "hot roll". When the high-temperature metal melt passes through the area in contact with the surface of the casting roll, the heat is quickly transferred to the roll to achieve solidification and crystallization; the solidified strip is rolled and acts as a "hot roll"; During the rolling deformation of the strip, the heat is transferred to the rolls, and the rolls continue to absorb heat. The inner surface of the roll and the cooling water, the outer surface and the surrounding medium are continuously exchanged during the continuous rotation of the roll, so that the surface of the part of the roll entering the working area can be in contact with the molten metal at a lower temperature to ensure the casting and rolling. The process went smoothly.

Casting and rolling technology is a cutting-edge technology in the field of metallurgy and materials. It is different from the production process of strips in the traditional metallurgical industry. Instead, it combines continuous casting, rolling, and even heat treatment in series to form a millimeter-scale strip. The billet is formed into an industrial product once after being rolled on-line. Casting and rolling technology has the following advantages:

1. The two processes of casting and rolling are completed on the same equipment at the same time. Compared with hot rolling, many processes such as ingot heating, blanking and hot rolling are eliminated, which reduces waste and saves energy.

2. The ingot milling surface is omitted, and the cutting and cutting ends after hot rolling are reduced, and the finished product rate is increased by 15% to 20%.

3. The equipment is simple and concentrated, with less investment, small floor space, fast construction speed and low production cost.

4. It can continuously and stably produce, simplify the production process of the factory, shorten the production cycle, greatly improve the production efficiency, and facilitate automation.

5. The quality of the rolled strip is no less than that of the traditional process, and it can also produce materials that are difficult to roll by traditional processes and new materials with special properties.

(III) Continuous casting and rolling technology of semi-solid magnesium alloy

Combining the horizontal double-roll continuous casting and rolling technology with the semi-solid processing technology, the obtained semi-solid strip continuous holding forming technology will be an all-Round efficient, energy-saving, short-flow, near-final forming processing method. Applying this technology to the processing and forming of the investment platform gold can be said to be a technology with international leading level and has certain innovation. This new metal strip production process not only fundamentally changes the traditional metal strip production method, even the production process that usually needs to be completed by casting, milling, heating, hot rolling, etc. It can be realized by casting and rolling, and the product quality control can be realized more conveniently.

When the alloy material having spherical crystals is heated to a semi-solid state, the deformation resistance is low, which is advantageous for roll forming. The semi-solid rolling process is a method in which the material to be rolled is heated to a semi-solid state and then fed into a roll. The test object is mainly the rolling forming of the sheet. The results show that the deformation and flow behavior of the rolled material in the bite-in area of ​​the roll are very different due to the different solid-phase ratio. When the solid phase ratio of the material to be rolled is high (for example, the solid phase ratio is 90% or more), the deformation and the solid metal hot rolling are substantially the same, and the internal solid phase component and the liquid phase component are rolled together to obtain uniformity. Rolled finished product. When the solid phase ratio is 70% or less, the flow and deformation of the liquid phase component and the solid phase component of the rolled material in the roll gap are separately performed, and the hydrostatic pressure caused by the pressure applied by the roll causes the liquid to start in the gap of the roll. The phase component overflows from the gap of the solid phase component and flows in the direction in which the pressure is reduced, that is, the liquid phase component flows out from the surface of the casting material from the inlet of the roll gap, is usually cooled and solidified by the roll, and is again introduced, and rolled into the gap of the roll. Finished product. The schematic diagram of semi-solid continuous casting and rolling is shown in the figure below.

The simulation of semi-solid magnesium alloy casting and rolling process is an important means to make the material forming process from experience to scientific guidance. It is a frontier field and research hotspot of material science and manufacturing science. Using computer simulation material forming process, the quality of the product can be predicted, the number of tests can be reduced; the optimal process flow can be determined to meet the requirements of a particular performance; the evolution history and spatial distribution of each physical quantity can be dynamically displayed; and the labor productivity can be improved. Therefore, numerical simulation analysis is an important part of the semi-solid magnesium alloy continuous casting and rolling technology.

Prospect of continuous casting and rolling technology for semi-solid magnesium alloy

The author believes that the continuous casting and rolling technology of semi-solid magnesium alloy will develop in the following directions:

(1) In-depth study on the preparation of semi-solid slurry, the quality of semi-solid slurry directly affects the quality of finished products after casting.

(2) At present, the research on flow transformation is only in the laboratory, the process is still immature, and there is still a certain distance from the application. Streaming into shape is more energy efficient, shorter in process, and more compact in equipment. Therefore, flow forming technology is still an important development direction for metal semi-solid processing technology in the future. In addition, the research on thixoforming technology is also the focus of future industrialization development and application.

(3) In the semi-solid continuous casting and rolling process, the research on numerical analysis of casting and rolling materials and rolls provides technical support for industrial production.

(4) When casting and rolling semi-solid magnesium alloys, on the one hand, it is necessary to ensure that the structure is fully deformed to achieve the purpose of improving the structure, so that there must be a certain amount of deformation; in addition, since the polycrystalline magnesium alloy has less slippage, the grains are macroscopically produced. Yielding tends to cause large stress concentrations in the grain boundaries, and the alloy is prone to intergranular fracture. Therefore, annealing and heat treatment techniques after rolling of magnesium alloy strips are also hot issues in future research.

(5) The application of semi-solid magnesium alloy continuous casting and rolling technology to industrial mass production will be in the next few years.

Fourth, the conclusion

With the improvement of smelting technology and the emergence of advanced molding technology and the reduction of manufacturing costs, magnesium-plated gold materials have been put into practical use. The modern metallurgical industry is developing in the direction of short process, energy saving, continuous, automation and high quality. The semi-solid magnesium alloy continuous casting and rolling technology has attracted more and more researchers' attention, laying a solid foundation for the further industrial production of magnesium alloy materials. technical foundation.

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