Effect of Annealing at 250℃ on Damping Capacity of As-cast ZA27 Alloy

摘要

The ZA27 alloy was prepared by metal mould casting, and then annealed at 250℃ for 1～4 hours. The damping capacities of the alloys were measured by using a testing apparatus based on the cantilever beam technique. The experimental results showed that the as-cast ZA27 alloy possesses high damping capacity with the value of 1.3x10~(-3) at 320Hz, and decreases to 1.1x10~(-3) after annealed at 250℃ for 1hour and then maintains the value as a constant even when the anneal time increases to 4hours. The microstructures of the as-cast ZA27 alloy consist of large dendrites of Al-rich primary α-phases, eutectoid (α+η) and non-equilibrium eutectic (α+η+ε). After the alloy is annealed at 250℃ for 1 h, the ε phase disappeared due to dissolving into the matrix and the space between flakes of eutectoid increased. Further increasing the annealing time has little effect on the space. The damping mechanism of the alloy was analyzed when considering thermoelastic damping and defect damping. In cantilever beam damping measurements, the value of thermoelastic damping accounts for only 7～8% in the overall damping, so it is concluded that the damping capacity of the ZA27 alloy should be mainly attributed to defect damping.