Influences of trace Al on as-cast microstructures and mechanical properties of Mg-Gd-Y-Nd-Zr alloy were investigated at room temperature by XRD（X-ray diffraction）

SEM（scanning electron microscope）and tensile testing.The phase constituent

deposition change of the composition and fracture mode of the alloy prepared were analyzed.The results show that the as-cast Mg-Gd-Y-Nd-Zr magnesium alloy is mainly composed ofα-Mg matrix and equiaxed eutectic phase with the size of 40μm approximately.Meanwhile

the composition deviation of ingot in axial is very low

and grain size is uniformly distributed in the ingot.The composition distribution exhibits apparently changes after adding trace Al

and difference of the grain size between the top and bottom appears remarkably.In addition

the mechanical properties of the alloy with trace Al are varied with locations and less than those of the Mg-Gd-YNd-Zr.Alloy fracture mode is mainly characterized by brittle fracture along the grain boundary with obvious secondary cracks.With Al addition

Al2 RE and Al3 Zr phases can be observed in the alloy

resulting in the heterogeneous distribution of composition in the melt as a result of deposition and leading to the great coarseness of the grain size because of the decrease of Zr content at the top.Due to the generation of Al2 RE and Al3 Zr phases

as-cast microstructure is deteriorated and elongation is decreased

and alloy crack is characterized by brittle fracture.