Recent work on the development of heat treatable wrought magnesium alloys
Fig. 1: A bright field TEM image and a 3D atom map obtained from Mg-1.2Al-0.8Zn-0.5Ca-0.4Mn sheet alloy after giving 2% tensile strain and artificial aging at 170oC only for 20 min. The formation of solute clusters and the segregation of the solute elements along the dislocation are readily visible.
Since age-hardening responses of magnesium alloys without rare earth elements are poor, precipitation hardening has not been used in conventional wrought magnesium alloys. However, microalloying often leads to substantial improvement of the age-hardening responses, opening up a possibility to develop heat treatable wrought magnesium alloys1). This talk presents our recent work on the development of heat treatable wrought magnesium alloys, which have comparable room temperature formability and strength with 6XXX series aluminum alloys.
One of the sheet alloys we have developed, Mg-1.2Al-0.8Zn-0.5Ca-0.4Mn (wt.%) sheet alloy, shows excellent room temperature formability with index Erichsen value of 7.7 mm after a solution treatment, and a high yield strength over 200 MPa after a T6 treatment2). Interestingly, this particular alloy shows bake-hardenabilty3). The sample showed substantial increase in the strength up to 240 MPa after giving 2% strain in tension followed by the artificial aging at 170oC only for 20 min. The strength increase may be explained by the formation of solute clusters and the segregation of the solute elements along the dislocation. This first BH Mg sheet alloy composed of only ubiquitous elements is highly attractive for application to automotive bodies.
Reference
1) K. Hono, C.L. Mendis, T.T. Sasaki, K. Oh-ishi, Scripta Mater. 63 (2010) 710-715
2) M.Z. Bian, T.T. Sasaki, T. Nakata, S. Kamado, K. Hono, Scripta Mater. 138 (2017) 151
3) M.Z. Bian, T.T. Sasaki, T. Nakata, Y. Yoshida, N. Kawabe, S. Kamado, K. Hono, Acta Mater. Under review