The effects of trace Sc and Zr on microstructure and internal friction of Zn-Al eutectoid alloy

The damping properties of Zn-22 wt.% Al alloys without and with Sc (0.55 wt.%) and Zr (0.26 wt.%) were investigated. The internal friction of the determined by the microstructure has been measured in terms of logarithmic decrement (3) using a low frequency inverted torsion pendulum over the temperature region of 10-230 degreesC. An internal friction peak was separately observed at about 218 degreesC in the Zn-Al alloy and at about 195 degreesC in Zn-Al-Sc-Zr alloy. The shift of the 3 peak was found to be directly attributed to the precipitation of Al-3(SC, Zr) phases from the alloy matrix. We consider that the both internal friction peak in the alloy originates from grain boundary (GB) relaxation, but the grain boundary relaxation can also be affected by Al-Sc-Zr intermetallics at the grain boundaries, which will impede grain boundary sliding. In addition, Al-Sc-Zr intermetallics at the grain boundaries can pin grain boundaries, and inhibit the growth of grains in aging, which increases the damping stability of Zn-22 wt.% Al alloy. (C) 2003 Published by Elsevier B.V.