Stress relaxation behavior of an aluminium magnesium silicon alloy in different temper condition.

Highlights • Activation volume in the presence of semi-coherent β'' precipitates is significantly lower compared to other microstructural features. • Effective stress is almost two times higher in the presence of semi-coherent β'' precipitates compared to other microstructural features. • Exhaustion rate of mobile dislocation density is negligible in the over-aged sample compared to solutionized and peak-aged sample. • Relaxation strain is higher in the presence of semi-coherent β'' precipitates compared to other microstructural features. Abstract In the present investigation, stress relaxation tests were carried out on an aluminium magnesium silicon alloy to determine rate controlling mechanism in different temper conditions. Single and multiple relaxation tests were carried out to determine apparent and physical activation volume. It was found that in the presence of solutes and incoherent precipitates, dislocation-dislocation interaction is the rate controlling mechanism, whereas dislocation-precipitate interaction is the rate controlling mechanism in the presence of semi-coherent precipitates. Moreover, the nature of deformation was found to be more viscous (higher strain rate sensitivity) in the presence of semi-coherent precipitates compared to other microstructural features (solutes, incoherent precipitates). Special emphasis is placed upon understanding exhaustion rate of mobile dislocation density during relaxation period. It was found that the exhaustion rate of mobile dislocation density is negligible in the presence of incoherent precipitates, whereas a significant reduction in mobile dislocation density was observed in the presence of solutes and semi-coherent precipitates. Furthermore, thermal and athermal components of the flow stress were determined to develop a comprehensive understanding regarding deformation behavior in different temper conditions. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]