HIGH TEMPERATURE CREEP OF Al-Mg ALLOYS.

Creep experiments were conducted on high purity Al and a range of Al-Mg solid solution alloys. For pure Al, creep occurs by a dislocation climb process and the stress exponent, n, is approximately 4. 4 over a wide range of stresses. For the solid solution alloys, there is a change from n approximately equals 4. 4 to n approximately equals 3. 0 with increasing stress due to the advent of viscous glide and the dragging of solute atom atmospheres. When the solute concentration is very small, as in Al-1% Mg, the stress exponent gradually increases from approximately 3. 0 with increasing stress, and ultimately there is a second dislocation climb region with n approximately equals 4. 4 and then power-law breakdown. The region of viscous glide with n approximately equals 3. 0 occurs over a wider range of stress at the higher solute concentrations, and this precludes the possibility of observing the second dislocation climb region in these alloys. The gradual increase in n above approximately 3. 0 in the viscous glide region is attributed to an increase in the value of m* above unity, where m* is the effective stress exponent for the dislocation velocity.