2023 Volume 73 Issue 7 Pages 315-321
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.
