Microstructural investigation of the failure mechanisms after creep exposure of Mg-Y-Nd-Zn-Mn alloy

Tensile creep tests of squeeze-cast Mg-3Y-2Nd-1Zn-1Mn (wt.%) magnesium alloy were performed at constant load. Measurement of grain-boundary sliding by observation of the offset of marker lines was carried out. The role of mutual orientation of neighbor dendrites and possible influence of active slip systems inside dendrites on the cavity nucleation was investigated by electron backscatter diffraction. Experimental results show that creep failure in this alloy takes place by continuous nucleation, growth, and coalescence of cavities on dendritic boundaries. A nucleation mechanism involving stress concentrations due to slip inside the grains is not probable. Additionally, although the total extent of deformation due to grain boundary sliding is small, the contribution of sliding to the origin of required stress concentrations necessary for cavity nucleation cannot be excluded.