Dislocation Analysis during High-Temperature Creep of Die-Cast Mg-Al-Ca Alloy

Abstract

  Tensile creep tests were combined with detailed transmission electron microscopy in order to characterize the dislocation movements during creep and explain the creep properties of the Mg-Al-Ca AX52 die-cast alloy at 473 K. TEM observations indicate that dislocations are introduced within the primary α-Mg grain interior in the die-casting process, which consist of both basal and non-basal segments. The non-basal segments of the dislocations, having smoother curvature in the as die-cast state, partially exhibit steps parallel to the basal plane during high temperature exposure. The basal segments of the dislocations bow out and glide on the basal planes under stress, and the jogs follow the basal segments with the help of climb during creep. The easy glide of the basal segments of the dislocations controls the creep rates immediately after the stress application of the creep tests, while the creep mechanism for the alloy has been identified as the dislocation climb. By comparing the dislocation movements for the Mg-Al-Ca AX52 die-cast alloy with those for the Mg-Al AM50 die-cast alloy, it is inferred that the eutectic intermetallic phase covering the primary α-Mg grains decreases the climb velocity of the jogs during creep.