The creep behaviour of rheo-diecast AZ91D (Mg-9Al-1Zn) alloy

The creep behaviour of a commercial AZ91D (Mg-9Al-1Zn) alloy processed by rheo-diecasting has been investigated in the as-cast, partial solution treated, and complete solution treated conditions, in the temperature range from 150 to 180 degrees C and the stress range from 40 to 100 MPa. The results confirm that solution treatment is applicable to AZ91D processed by rheo-diecasting due to the high integrity achieved. It is shown that solution treatment can largely decrease the minimum creep rate and extend the constant creep rate range of rheo-diecast AZ91D. The best-fit stress exponent is found to be around 5 in the as-cast, partial solution treated, and complete solution treated conditions, indicating that the mechanism for creep in rheo-diecast AZ91D is controlled by dislocation climb. The elimination of the beta-Mg17Al12 phase from the microstructure of AZ91D by solution treatment does not obviously affect the mechanism for creep in rheo-diecast AZ91D. This suggests that the P-M917AI12 phase does not play a critical role in the determination of the mechanism for creep in rheo-diecast AZ91D. (c) 2006 Elsevier B.V. All rights reserved.