Dependence of steady state creep rate on applied stress and temperature in Al-0. 06wt% Si

Creep experiments for Al-0.60wt% Si were studied at working temperatures: 300, 393, 498 and 573 K, and under different applied stresses; 0.5-150 MPa, for samples pre-annealed at various temperatures. The steady state creep results showed that the creep rate depends on the condition of the Si atoms present in the matrix; either as aggregates that prevent gliding of dislocations and cause hardening of the matrix (samples pre-annealed at low temperatures), or diffused into clusters inside the matrix causing dislocations to move and the grain boundaries to slide easily and to increase the creep strain (samples pre-annealed at higher temperatures). The analysis of the creep mechanisms showed that the as-received samples have an activation energy of 0.61 eV, independent on the applied stress, showing that, for this matrix where there are existing Cotrell atmospheres of aggregated Si atoms, the creep seems to be controlled by drag of the atmospheres in a globe reaction, independent on stress. But in case of samples pre-annealed at 673 K, where silicon atoms are diffused in the matrix, leaving dislocations free to move; the creep reaction needs lower energy. It was found that the calculated activation energy is less (0.30--0.60 eV), depending on the applied stress.