Abstract
Using internal friction measurements, changes in the microstructure of microcrystalline magnesium and magnesium with 1 and 3 vol. % of Al₂O₃ nanoparticles due to thermal treatment have been investigated in this work. Materials have been thermally treated at increasing temperature, and then the amplitude dependence of decrement was measured at room temperature. The thermal treatment influences character of the amplitude dependence of decrement in the composite material, while in pure Mg no influence has been estimated. Thermal stresses induced in the composite due to a difference between thermal expansion coefficient of matrix and ceramic particles may create new dislocations at elevated temperatures. These thermal stresses can achieve the yield stress value of the matrix and a microglide of new created dislocations as well as their annihilation can occur.

Key words
metal matrix composites, magnesium, internal friction, thermal treatment, thermal stress, dislocation generation, dislocation annihilation

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