The applications of magnesium alloy forging materials are expected to expand.

　　The applications of magnesium alloy forging materials are expected to expand, but cost remains a major bottleneck. As a result, the industry is actively pushing ahead with the development of new technologies to reduce expenses. One such innovation is the low-temperature magnesium alloy forging technology jointly developed by the Sustainable Materials Research Division at Japan's National Institute of Advanced Industrial Science and Technology (hereafter referred to as "AIST") and Miyamoto Industry Co., Ltd. (headquartered in Tokyo). This technology offers several key benefits by lowering the forging temperature.

　　China Forging Talent Network employs technology that pre-organizes and controls the forging materials, reducing the crystal grain size to below 10 μm. Subsequently, the material is forged using a servo stamping process under low-temperature conditions—specifically, below 200°C. In contrast, magnesium alloys are typically forged at much higher temperatures, around 400°C, often with the aid of solid lubricants.

　　However, if low-temperature forging around 200°C is achieved, it becomes possible to use water-soluble lubricants that are easy to handle and remove, while also extending the lifespan of the dies. This approach holds promise for reducing the cost of forged components and boosting production efficiency.

　　Additionally, low-temperature forging can also reduce costs associated with maintaining the temperature of heating furnaces and molds, while exhibiting minimal thermal expansion—a feature that helps enhance the dimensional accuracy of the finished products. Miyamoto Industries predicts that, thanks to these advantages, the technology could ultimately lead to a 20–30% reduction in current forging costs.

　　Reduce the crystal grain size to below 10 μm.

　　The process flow for the newly developed forging technology is as follows: First, the magnesium alloy intended for forging undergoes a "homogenization treatment," which involves heating the metal material to a specific temperature and holding it there for a set period, ensuring that alloy elements are evenly distributed throughout the material. Specifically, the material is heated to 410°C and held at this temperature for 24 hours, after which it is allowed to cool naturally in an ambient air environment. This process results in a microstructure with uniformly sized crystals ranging from 0.1 to 0.2 mm in diameter, ultimately forming the billet ready for forging.

　　Next, the process involves using a servo stamping machine to perform low-speed upsetting at 5–10 mm/s, shaping the billet—preheated to 300°C—until the reduction in height reaches 10%. This deformation induces strain within the billet, triggering the phenomenon of "dynamic recrystallization."

　　Dynamic recrystallization is the phenomenon in which metal regenerates new crystal grains during heating and stress-induced deformation, helping to dissipate strain energy. Under these conditions, the grain size of the billet can be reduced to approximately 5–10 μm (Figure 1)*. To achieve low-temperature forging, "such microstructural control is crucial," says Naofumi Saito, Senior Principal Research Scientist at the Sustainable Materials Research Division of the National Institute of Advanced Industrial Science and Technology (AIST). With materials featuring this refined grain structure, low-temperature forging becomes possible even below 200°C.

　　Figure: Grain Changes in Magnesium Alloy Caused by Forging at 1300°C

　　Utilize the dynamic recrystallization phenomenon to refine grain size. Although AZ31 still exhibits localized residual features,

　　Larger grains, but most of them have transformed into grains measuring around 5 μm. AZ61

　　Although the grain size is slightly larger than that of AZ31, it was still successfully refined into a finer microstructure after forging.

　　* Areas with crystal grain sizes of 10 μm or less account for approximately 95% of the total area.

　　"Although it still depends on where the material will be used, it demonstrates strength and ductility comparable to those of aluminum alloys," says Naofumi Saito. This makes it possible to forge heat sinks like the one shown in Figure 2, featuring散热柱 (heat sink fins) measuring approximately 8 mm in length.

　　After upsetting the homogenized billet at 300°C,

　　Cut and forge the material. The heatsink measures approximately 30 mm along each side at the base.

　　Thickness: 3.5 mm, with heat-dissipation posts measuring 2 mm square and 8 mm in height. AZ61 alloy can also be forged smoothly.

　　By dividing the process to reduce the temperature

　　This technology evolved from a forging technique jointly developed by Sogo Kenkyusho and the Japan Institute of Mould Materials between 2006 and 2010. The original method also leveraged the dynamic recrystallization phenomenon that occurs during forging, enabling the refinement of forging material grains to below 10 μm—a key factor that made low-temperature forging possible. During processing, the process begins by slowly pressing a billet heated to 300°C, triggering dynamic recrystallization. Once this stage is complete, the material is immediately transferred to the forging step for shaping. In other words, the entire sequence—from dynamic recrystallization to final forging—is accomplished in a single, seamless operation.

　　However, since the forging is performed at 300°C, a solid lubricant is still required, preventing the full realization of the advantages offered by low-temperature forging. Additionally, because upsetting and forging share the same die, the shapes that can be successfully formed through this process remain quite limited.

　　Moreover, Sankyo Research and Miyamoto Industries discovered that separating the low-speed upsetting process—designed to induce dynamic recrystallization—from the forging process can also reduce the forging temperature by approximately 100°C.

　　Expand the scope of applicable materials

　　Currently, only the magnesium alloys AZ31 and AZ61 have been confirmed to be forgeable at temperatures below 200°C. Moving forward, the National Institute of Advanced Industrial Science and Technology (AIST) and Miyamoto Industries will continue their research into enabling low-temperature forging for AZ91—known for its poor forgeability—as well as for flame-retardant magnesium alloys containing calcium. In particular, since increasing calcium content tends to reduce processing efficiency, the team plans to explore methods that maintain flame resistance while minimizing calcium levels, thereby improving overall manufacturing efficiency.

　　Meanwhile, the Productivity Research Institute and Miyamoto Industries will also strive to achieve forging processes that operate at temperatures below 100°C—further reducing heat levels. This approach is expected to significantly enhance production efficiency while cutting costs. If cold forging capabilities are successfully realized, it could even replace current forged components made from aluminum alloys and steel, paving the way for broader applications across industries such as automotive manufacturing.