TEM Interface Analysis

The Al-containing region at the interface centerline that explored with EPMA analysis has been studied by TEM. Samples for TEM were extracted from the center of interface flat region in a direction similar to SEM-EPMA samples. Ultrafine particles that distributed inside an Mg substrate were found in this region and DP (diffraction pattern) analysis on them are shown in Figure 14a,b.

Based on measurements completed on DP's, it was found that the substrate (Figure 14a) shows crystal structure that precisely matches the HCP structure of magnesium. The DP of particles indicated a material with lattice spacing values of 0.42 nm; 0.44 nm; and, 1.68 nm. According to library data, the closest match is a ternary composition of type MgCuxAly. Based on Buhler (1998) and Mel'nik (1981), the composition of MgCu1.1Al0.9 4H (hp24, P63/mmc), with cell parameters of 0.51 nm; 0.51 nm; and, 1.676 nm, that is a Friauf–Laves phase C36 is the nearest estimation [39,40]. Change in indices *x* and *y* were attributed to the non-stoichiometry intermetallic compounds. Other products in this ternary system do not match with our findings.

**Figure 14.** TEM analysis on joint type B (1100 J); diffraction pattern (DP) of (**a**) Mg matrix; (**b**) intermetallic compound (IMC) particles, at the interface centerline region.
