Creep behavior of AS41 alloy matrix nano-composites

Nano-alumina reinforced AS41 magnesium alloy matrix composites with 2 wt% and 5 wt% Al2O3 were fabricated by combined stir casting and ultrasonic processing in order to distribute the nano-alumina particles uniformly in the melt. Indentation creep tests were performed on the nano-composites and the as cast AS41 alloy at four different temperatures of 448 K, 473 K, 498 K, and 523 K and three different stresses of 109.2 MPa, 124.8 MPa and 140.4 MPa. The creep curves obtained in these tests show that creep resistance increased with the addition of nano-Al2O3 into the magnesium alloy, and nano-composites with 5 wt% Al2O3 exhibited highest creep resistance. The values of obtained stress exponent range from 3 to 3.5, 3.55 to 6, and 4 to 6.5 for the as-cast AS41 alloy, and AS41/2 wt% Al2O3, and AS41/5 wt% Al2O3 composites, respectively. Thus, dislocation creep is the dominant creep mechanism. The calculated activation energies for as-cast AS41, AS41/2 wt% Al2O3 and AS41/5 wt% Al2O3 are approximately 66.17 kJ/mol, 83.77 kJ/mol, and 88.3 kJ/mol, respectively. The activation energy values for the creep of composites are close to that of the pipe diffusion (92 kJ/mol) of magnesium.