**3.2 Tensile test of gravity-cast ingot**

The tensile test results for the gravity-cast Al-Mg alloys are plotted against the Mg content in **Figure 8**. As the Mg content increased from 4.5–10%, the tensile stress gradually decreased from 231 to 185 MPa, and the 0.2% proof stress gradually increased from 106 to 138 MPa. The elongation decreased greatly from 18–10% when the Mg content increased from 4.5–6%, after which it linearly decreased with further increases to the Mg content, down to 3% at an Mg content of 10%. The Mg content had a greater effect on the elongation than on the tensile stress or the 0.2% proof stress.

#### **3.3 Tensile test of hot-forged gravity-cast ingot**

The results of the tensile test of the hot-forged gravity-cast ingot are plotted against the Mg content in **Figure 9**. The tensile stress, 0.2% proof stress, and

*Characteristics of Al-Mg Test Pieces with Fe Impurities Fabricated by Die Casting, Roll Casting… DOI: http://dx.doi.org/10.5772/intechopen.100940*

**Figure 9.** *Tensile test results for hot-forged gravity-cast Al-Mg alloys.*

elongation of all Al-Mg alloys were increased by the hot forging. The tendencies of the tensile stress and elongation for the Mg content were also changed by the hot forging. The tensile stress increased with increasing Mg content. The increase (improvement) of the tensile stress became greater as the Mg content increased. At Mg contents of 4.5% and 10%, the tensile stress increased from 231 to 287 MPa and 185 to 270 MPa, respectively, which corresponds to respective increases of 56 and 185 MPa. When the Mg content was 8%, the elongation was maximized, and the elongation of the Al-10%Mg was the smallest among the alloys. The elongation of the hot-forged Al-8%Mg was 24%, and that of the Al-10%Mg was 17%. These results show that the hot-forged Al-Mg alloys have excellent strength and ductility.

Optical microscope images of the gravity-cast and hot-forged Al-Mg alloys are shown in **Figures 10** and **11**, respectively. The gravity-cast Al-Mg alloys had a dendrite microstructure, as shown in **Figure 10**; this is a typical structure for this type of casting. In contrast, there was not a dendrite structure in the hot-forged Al-Mg alloys, as shown in **Figure 11**, and the microstructure changed to a deformation structure as a result of the hot-forging. The grain size decreased as the Mg content increased until 8% Mg. This may contribute to the excellent mechanical properties of the Al-8%Mg alloy.

**Figure 10.**

*Optical microscope images of gravity-cast Al-Mg alloys.*

#### **Figure 11.**

*Optical microscope images of hot-forged Al-Mg alloys.*
