Dynamic Deformation Behavior Of AM80-2.0Ca Magnesium Alloy Under High Strain Rate

Magnesium alloy is one of the lightest metal materials in practical application. Magnesium alloy has a lot of advantages, such as good damping resistance, high specific stiffness, specific modulus and excellent electromagnetic shielding. Magnesium alloy is the third type of metal materials developed after the steel and aluminum alloy materials. It owns a reputation of "green engineering structural materials in the 21 st century" due to the low cost for recovery and little pollution to the environment.Dynamic compressive tests under different strain rate s were conducted on AM80-2.0Ca along the extruding and transverse directions by using a Split Hopkinson pressure bar(SHPB). The stress-strain curve is analyzed. The dynamic compression curves of AM80-2.0Ca magnesium alloy are simulated and corresponding Johnson-Cook constitutive equation is obtained by using nonlinear fitting. At the same time the effects of strain rate and loading dire ction on the magnesium alloy are investigated by means of optical microscopy(OM) and transmission electron microscope(TEM).Strain rate has a great influence on magnesium alloy AM80 2.0 Ca under high speed impact.The results show that for the AM80-2.0Ca magnesium alloy,with the increasing of the strain rate, the stress-strain curves show ascend trend at the first and then descend, and the maximum strain of AM80 magnesium alloy increased, implying that the AM80 magnesium alloy have positive strain rate effect.When strain rate reaches 3400 s-1, there is an obvious crack in the sample. The curve show s a concave type status along the extrusion direction and a convex type along the transverse direction. The maximum stress along the extrusion direction is bigger than the transverse direction under the same strain rate, indicating an obvious anisotropy phenomenon.The analysis of deformation microstructure demonstrates that the microstructure produced obvious change. The deformation mechanism is a combination of twinning and slipping. Besides the fracture, the failure modes of high strain rate belong to adiabatic shear band and crack propagation. At the beginning of the deformation stage, extension twining is the main deformation along the extrusion direction and contraction twining is the main deformation perpendicular to the extrusion direction. With the increase of the strain rate, non-basal-plane slips are activated and grain internal viscous sliding phenomenon is observed.Considering the influence of deformati on on strain-rate effect,the JC model is modified. For dynamic compression of AM80-2.0Ca along extruding directions, the modified JC model removes the part which represents the influence of strain rate on yield stress. After modification, the predicting re sults by JC model are consistent to testing results.