Research On The Superplasticity Of Al-1.44Mg-1.09Y Alloy

Aluminum and aluminum alloys are widely used in aerospace,chemical industry,transportation,electronics and many other industries and daily life with a series of advantages,which have become the second industrial usage metal materials after steel.The consumption of aluminum-magnesium alloy accounts for 60%of superplastic parts in superplastic field.The study on the quasi-superplasticity of Al-Mg alloy is significant in elucidating the theoretical value and practical application.In this thesis,we studied the superplasticity of Al-1.44Mg-1.09Y alloy produced by castex technology,and did the high temperature tensile experiments.By means of OM,XRD,SEM,TEM and calculation,we studied coarse-grained superplasticity of aluminum-magnesium alloy from microstructure,mechanical property and deformation mechanism.The longitudinal microstructure consists of homogeneous banded or elongated grains,the transverse micro structure consists of homogeneous nearly equiaxed grains of Al-1.44Mg-1.09Y alloy,and the grain size is 16.44?m Al-1.44Mg-1.09Y alloy has the tensile strength of 178MPa and the elongation of 18.84%.In the room temperature tensile experiment,stress-strain curve has obvious effect of PLC.High temperature tensile tests were conducted at temperatures ranging from 673K to 793K over initial strain rates ranging from 1.67 × 10-4 s-1 to 1.67×10-1s-1,and true stress-true strain curves were obtained.The maximum elongations of Al-1.44Mg-1.09Y alloy obtained was 212%at temperature of 793K and initial strain rate of 1.67 X 10-4s-1,and the strain rate sensitivity index values m at different tensile conditions were calculated.According to the analysis of high temperature tensile mechanics curves and the micro structure of the alloy,during hot deformation,the main softening mechanism is DRV,only at higher temperature the final stages of the tensile curve,DRX can occur slightly.The thermal deformation constitutive equations of Al-1.44Mg-1.09Y alloy were built,including phenomenological constitutive equation,the constitutive equation of the mechanism and the constitutive equation of dislocation density(K-M model).The first two models agree well with factual data,but traditional K-M model can't describe the changes of dislocation density of Al-1.44Mg-1.09Y alloy accurately in the hot deformation.Superplastic deformation mechanism of Al-1.44Mg-1.09Y alloy was studied,the real stress index nt=5,the real deformation active energy Qt values range from 127.378 kJ/mol to 141.536 kJ/mol.Main deformation mechanism is dislocation creep,and a deformation mechanism map of the transition from dislocation viscous glide to dislocation climb was established of Al-1.44Mg-1.09Y alloy.