Effects Of Er Element On The Microstructure And Mechanical Properties Of Mg-Gd-Y-Nd-Zr Alloy

Mg-Gd alloy series has broad application prospects in the aerospace field to its low density,high specific strength and high specific rigidity.However,a higher requirement for mechanical properties of magnesium alloys has been proposed in aeropaces filed,due to the rapaid development of aerospace industry.in order to further improve the mechanical properties of the Mg-Gd alloy series,effects of Er addition on microstructure and mechanical properties of Mg-8Gd-4Y-Nd-Zr alloy have been investigated using optical microscope,X-ray diffraction,Scanning electron microscope,transmission electron microscopy,hardness testing,conductivity measurement and tensile testing.The conclusions are listed as follows:(1)Addition of Er element can refine the grains of as-cast Mg-8Gd-4Y-Nd-Zr alloy.The grain size decreases as the amount of rare earth Er addition increases,when the amount of Er is in the range of 0.25-1%.The grain size of the alloy almost keep stable as the amount of Er addition increases when the Er content increases to 2%.The refinement mechanism of the alloy by the addition of rare earth Er elements can be summarized as follows: the addition of rare earth Er elements can effectively increase the supercooling degree of the solid-liquid front melt during the solidification of the alloy,and to some extent increase nucleation cores in the alloy.(2)Abnormal grain growth can be observed in local areas when the alloy is solution treated at 520?.The abnormally grown coarse grains will significantly reduce the deformation coordination ability among grains and cause the cleavage fracture of alloy,which significantly decrease the mechanical properties of the alloy.(3)The superior chemical composition of the cast alloy is determined to be Mg-8Gd-4Y-Nd-Zr-0.5Er,and the correponding heat treatment regine is 480?/12 h +215?/24 h.After heat treatment,the grain size of the alloy can be well controlled,and can effectively avoid abnormal growth of alloy grains.After solution treatment and aging treatment,the ultimate tensile strength of the alloy reaches 384 MPa,the elongation reaches4.1%.The ultimate tensile strength is increased by 26 MPa compared to the alloy without Er addition.(4)Complete dynamic recrystallization occurred during extrusion of the Mg-8Gd-4Y-Nd-Zr-(x)Er alloys.The second phase particles in the alloy are broken during extrusion.When the Er content is 2%,the alloy exhibits superior mechanical properties,with a ultimate tensile strength of 412 MPa and an elongation of 6.3%.The improvement of mechanical properties is mainly attributed to grain refinement and the breakage of second phase particles.