A study by internal friction and Young's modulus measurements has been made on high‐purity polycrystalline aluminum of the effects on dislocation damping by 1‐MeV electron irradiation in the temperature range 78–360 °K. These measurements confirm the presence of an internal friction ``peaking'' effect in aluminum in agreement with the defect dragging model proposed by Simpson and Sosin. In particular it is observed that during electron irradiation and for specific mechanical and thermal histories of the sample, the logarithmic decrement &dgr; increases and later decreases. The increase is found to be generally strain amplitude independent and to be highly structure dependent, disappearing after a suitable high‐temperature anneal. Simultaneous modulus measurements show little or no effect due to electron irradiation between 78 and 240 °K, but the modulus increases monotonically for irradiations above 240 °K. The corresponding point‐defect kinetics exhibit a complex annealing behavior.