Long-period stacking ordered structures in Mg-3Cu-1Mn-2Zn-1Y damping alloy
(1. Laboratory of Advanced Materials, Department of Materials Science and Engineering,
Tsinghua University, Beijing 100084, China;
2. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China)
Tsinghua University, Beijing 100084, China;
2. College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China)
Abstract: 14H, 18R and 24R long-period stacking ordered (LPSO) structures were observed in the as-cast Mg-3Cu-1Mn-2Zn-1Y damping alloy using transmission electron microscopy (TEM). These LPSO structures contained Mg, Y, Cu and Zn and thus they were quaternary phases. Sharp diffraction pattern of the 24R structure was obtained and the angle between and g10024R was measured to be 5.03°. During high resolution TEM observations, lattice fringes with two characteristic spacings were observed within the 24R structure. Based on the experimental results, 6H, 7H and three 8H are suggested as the building blocks of 18R, 14H and 24R structures, respectively. The 24R unit cell can be interpreted as the stacking of 8H building blocks in the same shear direction with a shear angle of about 5.03°. The imperfect 24R structures are in order or disorder arrangements of principal 8H and minor 6H blocks. This double-block structure model is also applicable to other reported defects in LPSO structures.
Key words: magnesium alloys; long-period stacking ordered structure; TEM; building block