A challenge for ultra-high strength Mg alloys without any addition of rare earths

2019 Fiscal Year Final Research Report

• Project/Area Number: 17H03413
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Structural/Functional materials
• Research Institution: Toyohashi University of Technology
• Principal Investigator: Miura Hiromi 豊橋技術科学大学, 工学(系)研究科(研究院), 教授 (30219589)
• Co-Investigator(Kenkyū-buntansha): 小林 正和 豊橋技術科学大学, 工学(系)研究科(研究院), 准教授 (20378243)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: マグネシウム合金 / 多軸鍛造 / 超微細粒 / 高強度

Outline of Final Research Achievements

Combined processes of multi-directional forgings under decreasing temperature conditions (dMDF) followed by MDFing at room temperature (rMDF) were applied to AZ91Mg and AZX61Mg alloys to attain ultrafine-grained structure and ultra-high strength. The gran size of the samples prepared by dMDF in advance was gradually decreased with increasing cumulative strain of rMDF and the tensile strength was increased. The ultimate tensile strengths achieved were 580 MPa and 520 MPa for AZ91Mg and AZX61Mg alloys, respectively. Therefore, 700 MPa was not attained. This was due to the b phase precipitation during dMDF and their suppression of mechanical twinning which cause grain refinement. It is concluded, therefore, dMDF before rMDF induces a negative influence on strengthening. Ultrafine-grained AZ80Mg was warm extruded by a mechanism of superplastic deformation to form a round tube and it possessed quite high strength of 414 MPa.

Free Research Field

材料工学

Academic Significance and Societal Importance of the Research Achievements

希土類の添加を必要としない超高強度マグネシウム合金の開発は、我が国の材料戦略上極めて重要であり、特に超々ジュラルミン代替材として構造部材に適用できれば、我が国の新技術・新産業分野開拓に及ぼすインパクトは極めて大きい。 世界的に研究ブームとなっている巨大ひずみ加工を難加工材であるマグネシウム合金に適用し、これまでの2倍近い強度を達成する技術開発と材料組織設計は、学術的にも極めて波及効果が大きい。