In our previous study, Al-4.5Mg-1.0Mn based alloy with addition of both Si, Sr, Ti, B and hydrogen over 0.5 ml/100 gAl was developed with around 15% of fracture elongation and low hot tearing susceptibility (HTS). It was suggested that the mechanism of HTS reduction by the addition of Sr should be attributed to the decrease in the tensile thermal load due to the formation of hydrogen gas porosity at a relatively low solid fraction under the solidification shrinkage is constrained. In this study, we verified the above hypothesis by using acoustic emission (AE) method. The effect of the hydrogen content and Sr addition on AE signals were examined in the constrained castings during solidification. As a result, it was found that AE peak volts which indicates the occurrence of shrinkage and/or gas porosity were reduced under the condition with 1.0 ml/100 gAl hydrogen and Sr. By the addition of hydrogen, AE signals from non-constrained castings during solidification indicated that the formation of hydrogen gas porosity reduced the AE peak volts. These results revealed that the addition of 1.0 ml/100 gAl hydrogen and Sr reduces the AE peak volts due to the promotion of hydrogen gas porosity. Therefore, the hypothesis should be reasonable.

Recycling Al scraps is extremely important to achieve carbon neutrality. However, almost all impurity elements cannot be easily removed by oxidation and evaporation once dissolved in molten Al alloy. Therefore, it is necessary to develop an impurity removal process in molten Al. Iron is one of the impurity elements in Al, which easily forms intermetallic compounds with Al. On the contrary, Fe is immiscible with Mg in the liquid state. These facts suggest that the repulsive interaction between Fe and Mg in molten Al alloy enhances the precipitation of such intermetallic compounds as Al₃Fe. This study proposed the Fe removal method from molten Al alloy by the precipitation of the Al₃Fe inter-metallic compound by adding Mg. Molten Al-Mg alloy was equilibrated with Al₃Fe, and the Fe content of molten Al-Mg alloy was investigated. Fe content decreased with increasing Mg content, and this method was proved to be adequate for removing Fe from molten Al-Mg alloy. The standard Gibbs energy change for the precipitation of Al₃Fe at 873 K and the activity coefficient of Fe in molten Al-Mg alloy as a function of Mg content and temperature have been derived from the experimental results.

Using the derived values, the removal limit of Fe in molten Al-Mg alloy in the present method was discussed. Fe content can be decreased at higher Mg content and lower temperature, and the lowering limit of Fe is 0.0029 mass percent at the eutectic point of Al-Mg alloy.

Scandium addition to aluminum alloys has been evaluated at various research institutions, and it is known that the Al₃Sc precipitates effectively increase their strengths. In this study, the effect of Sc addition on the strengths of two types of 7000 series aluminum alloys was investigated. As a result, the strength increased by the Sc addition to both types of alloys, but the increased amounts were limited to 10-40 MPa. It was considered that because the strengthening effect by the η’ phase was sufficiently high, the precipitation strengthening by the dispersion of Al₃ (Sc_1-xZr_x) particles was relatively low in these alloys.