The application of magnesium alloy forging materials is expected to expand

The application of magnesium alloy forging materials is expected to expand, but the cost becomes its bottleneck. Therefore, the industry is actively promoting the development of new technologies to reduce costs. The low-temperature magnesium alloy forging technology developed by the sustainable materials research department of the Comprehensive Research Institute of Industrial Technology of Japan and Miyamoto Industrial Co., LTD. (Headquarters: Tokyo) is one of them. This technology can obtain many benefits by reducing forging temperature.

The technology controls the microstructure of the forged material in advance, so that the crystal particle size is reduced to less than 10μm, and then the servo stamping process is used to forge at low temperature (below 200℃). Magnesium alloys are generally forged at a high temperature of about 400℃, and solid lubricants are used.

However, if low temperature forging is achieved at around 200℃, water-soluble lubricants that are easy to handle and remove can be used, and the life of the die can be extended. This is expected to reduce the cost of forging components and improve production efficiency.

In addition, low temperature forging can also reduce the cost of keeping the temperature of the furnace and the die, and the temperature expansion is very small, which helps to improve the dimensional accuracy after forming. Miyamoto Industry forecasts that with these advantages, it is expected to reduce the current forging cost by 20 to 30 percent.

Reduce the crystal size to less than 10μm

The forging technology is developed as follows: First, the forging magnesium alloy is "homogenized", that is, the metal material is heated to a certain temperature and held for a certain time, so that the alloying elements are uniformly dispersed in the material. During the specific operation, the material is heated to 410℃ and kept for 24 hours, and then cooled naturally in the air environment. Thus, the metal structure with a uniform crystal size of 0.1 ~ 0.2mm can be obtained, so as to form the blank for forging.

The next step is to use a servo punching machine, upsetting at a low speed of 5 ~ 10mm/s, to process the billet heated to 300℃ until the reduction rate reaches 10%. In this way, strain occurs in the billet and "dynamic recrystallization" occurs.

Dynamic recrystallization is a phenomenon in which the metal reforms into crystalline particles in order to eliminate strain energy during the process of heating and stress deformation. Under the above conditions, the crystal size of the billet can become about 5-10 μm(FIG. 1)*. For forging to be cryogenic, "such organizational control is very important" (Naofumi Saito, senior senior researcher at the Sustainable Materials Research Division of the Institute of Industrial Research). For this kind of material with fine crystal size, it can be forged at low temperature below 200℃.

Figure. Grain changes of magnesium alloy caused by upsetting at 1300℃

Dynamic recrystallization was used to refine the grains. AZ31 Although localized residue

Large grains, but most of them become about 5μm grains. AZ61

Although the grain size is slightly larger than AZ31, the microstructure is also realized after upsetting.

* About 95% of the crystal size is less than 10μm.

"It still depends on where the blank is used, but it shows the same strength and tensile properties as aluminum alloy" (Saitou Naofumi). In this way, it is possible to forge a radiator of the type shown in Figure 2, with a length of radiator column of about 8mm.

After upsetting the homogenized billet at 300℃,

Cut material and forge. The size of the heat sink is, the bottom side length is about 30mm,

The thickness is 3.5mm, the cooling column is 2mm square and the height is 8mm. Smooth forging with AZ61

Reduce the temperature through the division process

The technology is developed from the forging technology jointly developed by the Integrated Research Institute and Japan Plain Wood Center from 2006 to 2010. The original technique also utilizes the dynamic recrystallization during forging process to fine the grains of the forged materials to less than 10μm, thus achieving low temperature forging. During processing, the billet heated to 300℃ is pressed at a low speed at the beginning to cause dynamic recrystallization phenomenon, and then directly into the forging process for forming. That is, the process from dynamic recrystallization to forging is handled in a single process.

However, because it is forged at 300℃, solid lubricants are still used, which cannot give full play to the advantages of low temperature forging. In addition, upsetting uses the same die as forging, so the shapes that can be forged are limited.

By separating the low-speed upsetting process, which is intended to cause dynamic recrystallization, from the forging process, the research institute and Miyamoto found that the forging temperature could be reduced by about 100℃.

Expand the range of applicable materials

At present, only AZ31 and AZ61 magnesium alloys have been confirmed to be able to be forged at temperatures below 200℃. In the future, the institute and Miyamoto will also study how to achieve low temperature forging of AZ91 and flame-retardant magnesium alloys with calcium added. The latter, in particular, is looking for ways to increase processing efficiency by reducing calcium content while maintaining flame retardancy, as high calcium content reduces processing efficiency.

At the same time, the Institute and Miyamoto Industrial will also strive to achieve further temperature reduction below 100℃ forging. This is expected to further improve productivity and reduce costs. If it can reach the level of cold forging, "it can also replace the current forging products made of aluminum alloy and steel, which is expected to be popularized in a wide range of fields such as automobiles"