Effect of precipitation aging on the fracture behavior of Mg-11Gd-2Nd-0.4Zr cast alloy

The effect of precipitation aging on fracture behavior of Mg-11Gd-2Nd-0.4Zr cast alloy at room temperature has been studied in this paper. The transition of fracture mode as a function of temper state can be generally described as follows: ductile transgranular fracture in as-quenched condition, transgranular cleavage fracture in peak-aged condition and intergranular fracture in overaged condition. The transgranular cleavage fracture is attributed to the planar slip arising from the dislocation shearing of strengthening precipitates in matrix. The intergranular fracture is explained to occur as a result of the growth of grain boundary precipitates (GBPs) and precipitate free zones (PFZs) via two different types of mechanism, i.e. decohesive rupture accompanied by intergranular facets with ledges in slightly overaged specimen with fine GBPs and narrow PFZs, and dimple rupture in substantially overaged specimen with coarse GBPs and wide PFZs. (c) 2007 Elsevier Inc. All rights reserved.