Hot Compression Behavior and Processing Map of Mg-9Gd-2Nd-0.8Al Alloy
The microstructure of as-cast and homogenized Mg-9Gd-2Nd-0.8Al alloys was studied by an optical microscope and a scanning electron microscope.Then the hot compression experiment of homogenized alloy was carried out with Gleeble-1500D thermal simulation under the conditions of deformation temperature of 350-500 ℃ and strain rate of 0.003-1 s-1.The deformation activation energy of the alloy was calculated,and the constitutive equation and hot processing map of the alloy were constructed and analyzed.The results show that as-cast Mg-9Gd-2Nd-0.8Al alloy is mainly composed of α-Mg matrix and Mg5Gd,Mg41Nd5,A12RE phases.After homogeniza-tion treatment(510℃×12 h),Mg5Gd and Mg41Nd5 phases basically dissolve and A12RE phase remains stable.The flow stress curve of homogenized alloy shows the characteristics of dynamic recrystallization.The flow stress and peak stress decrease significantly with the increase of temperature or the decrease of strain rate.The defor-mation activation energy of the alloy is 185.836 kJ·mol-1.There are two instability zones within the deformation conditions of this test:deformation temperature of 350-375 ℃,strain rate of 0.003-0.012 s-1 and deformation temperature of 350-500℃,strain rate of 0.05-1 s-1.The best processing zone is deformation temperature of 445-500℃,strain rate of 0.003-0.01 s-1.The recrystallization mode of the alloy under the deformation tempera-ture of 400 ℃ and strain rate of 0.003 s-1 is mainly discontinuous dynamic recrystallization.