Combined Effect of Solution and Dispersion Hardenings at High Temperature

In order to clarify the combined effect of solution and dispersion hardenings at high temperatures, the internal stress, the effective stress and dislocation density in Al-3 at% Mg-1 at% Mn alloy have been measured and compared with those in Al-3 at% Mg alloy. The measurement has been carried out by applying the stress-relaxation technique to the steady-state tensile deformation at temperatures from 573 to 723 K and at strain rates from 3×10−5 to 3×10−3 s−1.It is found that the additive rule of hardenings by solute Mg atoms and dispersed Al6Mn particles holds in the low Z region, but the effect of dispersion hardening decreases with the increase of Z, where Z is the Zener-Hollomon parameter. This behavior is explained by the relative value of the inter-dislocation spacing to the inter-dispersoid spacing. In the low Z region where the dislocation spacing is larger than the dispersoid spacing, nearly all dislocations undergo the resistance of dispersoids, and the additive rule holds. In the high Z region, however, the dislocation spacing becomes smaller than the dispersoid spacing, and the part of dislocations not directly contacting with the dispersoids increases as Z increases, resulting in the decrease of the effect of dispersion hardening.