**2. Materials and Methods**

#### *2.1. Sample Preparation*

The ingots of Al-6Mg alloy were prepared in an electric resistance furnace by the casting of pure Al and Mg + Al2Ca master alloy. The ingots were homogenized at 420 ◦C into a plate with an extrusion ratio of 21.7:1. The initial extrusion thickness was 12 mm. The alloy was cold-rolled to 3 mm by using a 2-high mill rolling machine (FENN, East Berlin, CT, USA). The cold-rolled specimen was further annealed at 420 ◦C for 1 h in a box furnace and air-cooled. Finally, the alloy was cold-rolled with 20% reduction (CR20 alloy) and 50% reduction (CR50 alloy), respectively. The chemical composition of the Al-6Mg alloy is shown in Table 1. The chemical composition was measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, SPECTRO).

**Table 1.** Chemical composition of Al-6Mg alloy (wt.%, measured by ICP-AES).

