Dynamic Mechanical Behavior Of AM80 Magnesium Alloy Under High Speed And Heavy Load And Its Basic Model

Magnesium alloy is one of the most ideal lightweight materials in automotive and aerospace fields because of its excellent electromagnetic shielding,extremely low density and good shock absorption performance.In this paper,the Hopkinson pressure bar device was used to study the dynamic stress behavior of two kinds of AM80 magnesium alloys(cast and extruded consitions)with temperatures ranging from 298 K to 623 K and loading strain rates ranging from 1100 s-1 to 5900 s-1.The microstructure evolution of as-cast AM80 magnesium alloy under different deformation conditions was analyzed by optical microscope,and the influence of microstructure on the stress response behavior was investigated.Based on the experimental data,the dynamic mechanical constitutive models of as-cast and as-extruded AM80 magnesium alloys were constructed,respectively.The results were as follows.(1)The stress response behavior of as-cast AM80 magnesium alloy is sensitive to loading strain rate,which also depends on the deformation temperature.However,the flow stress decreases with the increases of strain rate at medium to high strain,showing a critical strain rate for the transformation of strain rate sensitivity.(2)The microstructure of as-cast AM80 Mg alloy under dynamic impact mainly consists of high-density deformation twins and adiabatic shear bands,accompanied by a large number of secondary twins.With the increase of deformation temperature,the dynamic recrystallization occurs.With the further increase of deformation temperature,the degree volume fraction of dynamic recrystallization increase,and the recrystallized grains also grow up to a certain extent.(3)By optimizing the strain hardening term,strain rate strengthening parameter C and material strain hardening parameter n of the original J-C constitutive equation,the dynamic mechanics constitutive which can accurately describe the rheological behavior of as-cast AM80 magnesium alloy under a wide range of deformation temperature and strain rate has been constructed.The correlation coefficient(R)and mean relative error(AARE)are 0.987 and 3.88%,respectively.(4)The extruded AM80 magnesium alloy shows obvious anisotropy along the ED and TD directions.At 298 K,the flow stress curve of the ED samples is S-shaped,while the flow stress curve of the TD samples alloy is C-shaped.With the increase of strain rate and deformation temperature,the curve of the studied alloy in the ED gradually changes from S-shape to C-shape,which reduces the difference between the ED and TD samples,and weakens the anisotropy of the studied alloys finally.(5)According to the difference of mechanical behavior of extruded AM80 magnesium alloy under different loading directions,the strain hardening term and temperature softening term of the original J-C constitutive model were optimized.The dynamic mechanical constitutive models that can accurately predict the flow stress variation of the studied AM80 magnesium alloy along ED and TD were constructed.The correlation coefficients(R)of the two constitutive equations on different loading directions are 97.72%and 99.25%,and the relative absolute errors(AARE)are 3.52%and 1.96%,respectively.