Abstract
Precipitation processes in magnesium alloy AM20 have been studied. Homogenised alloy was annealed step by step at increasing upper temperature of the thermal cycle. Amplitude dependences of decrement and modulus defect were measured after each annealing step. While amplitude independent part of decrement was not influenced by the thermal treatment, the amplitude dependent part varies with the annealing temperature. Results were analysed according the Granato and Lucke theory of thermally activated break away of dislocation segments from solute atoms. Precipitation process(-es) decrease(s) number of solute atoms and increase(s) the length of free dislocation segments which are mainly responsible for damping behaviour of the alloy. Precipitation process(-es) occur(s) in the temperature interval from 200 to 320°C. These results were confirmed by stress relaxation tests.

Key words
internal friction, dislocations, precipitation, magnesium alloys

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