Dislocation Analysis of a Mg–Al–Ca Alloy by Transmission Electron Microscopy

Hiromu Hisazawa*, Asahi Nomoto** and Yoshihiro Terada**
*Graduate School of Technology, Industrial and Social Sciences, Tokushima University, Tokushima 770-8506, Japan
**Department of Materials Science and Engineering, School of Materials and Chemical Technology,
Tokyo Institute of Technology, Yokohama 226-8502, Japan

The dislocation structure was analyzed in a Mg–4.98Al–1.46Ca (mass%) alloy using invisible criterion with transmission electron microscopy. Basal and non-basal segment of dislocation induced during die-casting is determined as much <a> and a few <a + c> dislocation. After the aging at 523 K for 10 h and tensile deformation at 473 K, only basal <a> dislocation can be observed. This dislocation structure is not observed in crept specimens, which support the difference in dominant strengthening mechanism between creep and tensile deformation.

Table 1 shows the chemical composition of the Mg–5Al–1.5Ca alloy used in this study (in mass%). Table 2 shows the g · b invisibility criterion for perfect dislocations in the hexagonal close-packed crystals close to the [1-210] zone axis. Figure 1 shows the TEM bright field images of the as die-cast Mg–5Al–1.5Ca alloy, taken with B = [1-210]. The g vector is 10-10 (a), 10-11 (b) and 0002 (c), respectively. The <a + c> dislocation is indicated with an arrowhead in (c). Figure 2 shows the dislocation substructures developed after tensile test at 473 K/4.6 10-5 s-1 for the Mg–5Al–1.5Ca alloy aged at 523 K for 10 h, taken with B = [1-210]. The g vector is 10-10 (a), 10-11 (b) and 0002 (c), respectively. The introduced strain during tensile test is 5.6%.

[Published in Journal of the Japan Institute of Light Metals, 68 (2018), pp. 552-554]

Table 1 Chemical composition of the Mg–5Al–1.5Ca alloy used in this study (in mass%).

Table 2 The g · b invisibility criterion for perfect dislocations in the hexagonal close-packed crystals close to the [1-210] zone axis.

Fig. 1 TEM bright field images of the as die-cast Mg–5Al–1.5Ca alloy, taken with B = [1-210]. The g vector is 10-10 (a), 10-11 (b) and 0002 (c), respectively. The <a + c> dislocation is indicated with an arrowhead in (c).

Fig. 2 Dislocation substructures developed after tensile test at 473 K/4.6 10-5 s-1 for the Mg–5Al–1.5Ca alloy aged at 523 K for 10 h, taken with B = [1-210]. The g vector is 10-10 (a), 10-11 (b) and 0002 (c), respectively. The introduced strain during tensile test is 5.6%.