Effect of precipitation on internal friction of rapidly solidified AlSi alloys

Abstract

The internal friction of rapidly solidified AlSi alloys with compositions of 0.96, 3.8 and 11.5 at.% Si was studied using a low frequency inverted torsion pendulum over the temperature region of 300–600 K. An internal friction peak was observed in the temperature range 350–550 K in the AlSi alloys. The Q −1 peak decreased during the second run, which was found to be directly related to the precipitation of silicon solutes from the supersaturated aluminium grains. We suggest that the internal friction peak in the AlSi alloys originates from grain boundary relaxation, but the grain boundary relaxation can also be affected by the silicon precipitates at the grain boundaries, which will impede grain boundary sliding. This makes the internal friction peak much smaller than that of a pure polycrystalline aluminium. The internal friction behaviour of the Al-3.8at.%Si alloy was investigated in more detail. The increase of the internal friction peak height with increasing annealing time in the Al-3.8at.%Si alloy may be attributed to the coarsening of the silicon precipitates at the grain boundaries.