Damping Capacity Of 7075 Aluminum Alloy Base Matrix Composites Reinforced With Bi-Sn Coated Al₁₈B₄O₃3 Whisker

This paper systemly studied how coating on whisker influence damping properities of the surface coating on aluminum borate whisker reinforced aluminum and zinc based composites, coating materials were Bi and Sn. Prepared by squeeze casting material, whose mass ratio of coating material and the aluminum borate whisker of 1:10, volume fraction of whiskers in composites is 20%By testing methods such as SEM, XRD, TEM to analysis microstructure of surface coating aluminum borate whisker reinforced aluminum and zinc based composite material, and the effects of temperature, frequency, strain amplitude, whisker surface coating, heat treatment and solid solution - aging on the damping properties of composite materials.SEM and XRD results showed that the whiskers uniformly dispersed in the matrix,and interface phase dispears discontinuously in the interface of matrix and the whisker, during the preparation of composite materials follow-up this interface phase react with the matrix, finally introduces a low melting point interface phase Bi(Sn) into the matrix/reinforcement interface. The introduction of interface phase improved matrix / reinforcement interfaces and the state of dislocation in matrix, and causing damping capacity and behaviors of composite changes.Two peaks were found in spectrum of the damping and temperature of Bi coating composite. The low temperature peak named P1 while the medium temperature named P2, in the Sn coating composites damping-temperature spectrum, there appears a medium temperature damping peak P1. In the testing range, the damping value decreases with frequency increasing, and rapidly increases in the increase of strain.Studies on the relationship between peak position and frequency studies showed that the damping capacity increases with the frequency goes down, and the peak position moves to higher temperature, this meet the Arrehenius relations, means that the damping peaks are subject to thermal activation. Studies on the damping-temperature spectrum under different strain amplitude showed that dominant damping mechanism of the medium temperature peak changed from the interface phase of the melting damping into to the matrix/reinforcement interface damping, and when the temperature exceeds 300℃, the main damping mechanism is grain boundary damping.Damping-strain spectra under room temperature of composite materials showed that coating can improve the damping capacity at room temperature.With the increase of the strain amplitude the damping capacity can divide into two parts, associated with and without strain amplitude, the second part can also make up of two stages, increases slowly and increase rapidly, corresponding to dislocation damping and interface micro-slip damping mechanism.The damping temperature spectra of coating composite after heat treatment with show that higher the heat treatment temperature is, the better the damping properties of composite materials will be, low temperature peak with the preservation movement to the high temperature, while the peak temperature with the insulation temperature moves to lower temperature . The damping properties of annealed is better than quenched. In Sn coating composite, there will be a solid solution hardening phenomenon after 350℃heat treatment, the damping mechanism is changed, by the Sn melt damping into the melting melt of Sn-Zn eutectic damping.Solution and aging treatment to composite materials containing coating improve the damping properties, and the solution among interface phase and Al, Zn in matrix will change the damping mechanisms in the medium temperature peak.