Effects of shot peening on internal friction in cp aluminum and aluminum alloy 6008

Abstract

Abstract The strain-amplitude-dependent damping of bending beams of aluminum alloy 6008 and CP aluminum was measured at room temperature after different heat treatments and after shot peening. Shot peening led to an increase of damping in almost the whole measured amplitude strain range from 10 – 6 to 10 – 3 for CP aluminum. Strong ageing effects at room temperature were observed immediately after the shot peening process, namely an increase of the amplitude dependent part and a decrease of the amplitude-independent part of damping. After about 2700 h, ageing of the samples had saturated. For aluminum alloy 6008 much smaller ageing effects were found being due to compensating effects like formation of Cottrell clouds, precipitation of G.P. – zones, and the reduction of foreign atoms in solid solution. The found amplitude-dependent damping can be explained by the reversible movement of dislocations between strong pinning points like, e. g., precipitates and weak pinning points like solid solute atoms as proposed by the dislocation damping theory of Granato and Lücke. Using this model the found ageing effects can be explained by the diffusion of solid solute atoms to the dislocations.