Internal Friction Peak and Damping Mechanism in a High Damping Aluminium Alloy Laminate

An aluminium alloy laminate is developed which is characterized by high damping, corrosion resistance and weldability. The laminate is a kind of composite material which is made of two anti-corrosive layers (Al), two damping layers (ZnAl alloy) and one reinforcing layer (AlMg alloy) through hot rolling. The damping characteristics of the laminate is investigated and it is revealed that there is an internal friction peak at about 50℃ in curves of internal friction vs temperature. The activation energy of the peak was calculated. The origin of the peak and the damping mechanism is researched by means of SEM, TEM, X-ray and DSC. It is considered that the peak is caused by the interaction between dislocations and point defects in damping layers (AlZn alloy). i.e. the movement of dislocations dragging point defects under the action of the thermal-activation. During the remaining of the laminate at normal atmospheric temperature for a long time, the peak will weaken and even disappear with the restoration of the crystal microstructure and the reduction of the dislocation density in ZnAl alloy layers. The mechanism of the peak is in conformity with that of the dislocation inducted damping.