Influence of Cold-Working on Damping Characteristics of Al-Zn Alloys

Abstract

Effect of cold-working on the damping of furnace-cooled or water-quenched Al-Zn alloys with 0-100%Zn was studied by varying the reduction in area. Measurements of the logarithmic decrement δ and the regidity modulus G were carried out by the inverted pendulum method at a frequency of 1 Hz. The hardness Hv was measured using a micro-Vickers hardness tester, and the specific weight S by the Archimedean method.
Except for the water-quenched alloys with 70-90%Zn, the heat-treated alloys have generally a low δ. The order of magnitude of δ in the alloys subjected to heat-treatments depends on the viscous flow at the grain boundary between α and β phases. Upon cold-working, the δ becomes considerably larger with increasing reduction in area. The increase in δ is due to the increasing boundary effect resulting from the refinement of grains and to the increasing viscous and hysteretic motions of dislocations.
Hv values of the alloys with 10-70%Zn water-quenched from 673 K are considerably higher than those for furnace-cooling. On the other hand, the alloys with 80-90%Zn furnace-cooled show Hv values higher than those water-quenched. The nearer the eutectoid composition, the lower becomes the Hv value after cold-working. G values of the alloys water-quenched from 573 K or furnace-cooled from 573 and 673 K increase with increasing Zn content, while those after water-quenching from 673 K show a minimum value at 50%Zn. The G upon cold-working is nearly constant up to 40%Zn and increases rapidly with Zn content in excess of 40%, regardless of the prior heat-treatment. The S increases with Zn content, but the value is generally as small as 4.8 Mg/m³ even for the Al-70%Zn alloy.