Effect of strontium addition on hydrogen content and porosity shape of Al-Si alloys

The HYSCAN II instrument has been used to measure hydrogen content in unmodified and modified hypoeutectic Al-10wt%Si alloys. Experimental results show that the hydrogen content of the melt increases markedly after strontium addition, reaches a maximum value after a certain time, and then decreases and tends to be close to the initial hydrogen level. In contrast in unmodified melts, hydrogen content decreases with time, and finally reaches a stable level. Moreover, porosities in unmodified samples are found to be long, fissured and irregular. In modified samples, however, porosities are broad, rounded and regular. The mechanism of the effect of strontium addition has also been discussed.