Yoshihito Kawamura

Abstract:

Mg alloys are attractive for use in aircraft components primarily because of their low density and high specific strength. But current commercial Mg alloys, e.g., AZ31, have low yield strength and unacceptably low ignition temperature. Moreover, several years ago America’s FAA (Federal Aviation Administration) has lifted the ban on the use of some Mg alloy forms in the payload area and has set up a standardized testing method of flammability for Mg alloys [1].
We have developed two kinds of high-strength Mg alloys with a high ignition temperature: 1) Mg-Zn-Y alloys consisted of alpha Mg phase and a long period stacking ordered (LPSO) phase [2,3,4], and Mg-Al-Ca alloys consisted of alpha Mg phase and a C36-type intermetallic compound [5].
The LPSO-type Mg₉₆.₇₅Zn₁Y₂Al₀.₂₅ alloy, which was produced by hot extrusion of cast ingot, exhibited very high, symmetrical yield strength in both tension and compression, high heat resistance, and great flame resistance. Its corrosion resistance is the same as AZ31. The LPSO phase, which has a periodical stacking structure of the 4 atomic layers consisting of in-plane ordering of L1₂ Zn₆Y₈ clusters and the 1-4 atomic layer(s) of 2H Mg, is strengthened by kinking, which was formed during the hot extrusion. This kink strengthening is a brand-new concept for strengthening mechanism of materials. On the other hand, the C36-type Mg₈₄.₉₇Al₁₀Ca₅Mn₀.₀₃alloy, which was also produced by hot extrusion of cast ingot, exhibited high, symmetrical yield strength, high corrosion resistance, and nonflammability; the ignition temperature is higher than the boiling temperature of pure magnesium. These advanced Mg alloys have passed the FAA flammability test for Mg alloys.
The development of more sustainable and more affordable manufacturing technology for these next-generation Mg alloys has been conducted via an integrated and comprehensive collaboration between academia and industry. Moreover, the applications and commercialization of these advanced Mg alloys have been under serious investigation and study for automobile, aircraft, and biomedical industries.

[1] T.R. Marker, DOT/FAA/AR-11/3.
[2] Y. Kawamura, K. Hayashi, A. Inoue and T. Masumoto, Mater. Trans. 42 (2001) 1172-1176.
[3] Y. Kawamura and S. Yoshimoto, Magnesium Technology 2005 (TMS, 2005, pp499-502).
[4] E. Abe, Y. Kawamura, K. Hayashi and A. Inoue, Acta Materialia 50 (2002) 3845-3857.
[5] Y. Kawamura and A. Inoue, Materials Science Forum 419-422 (2003) 709-714.