Study On The Crashworthiness Of Extruded Mg-3Zn-1Y Magnesium Alloy

As the lightest engineering structural materials,magnesium alloys have been widely used in the aviation,aerospace,automotive and electronic products and other industrial fields,due to their high specific strength and stiffness,good electromagnetic shielding and damping properties,etc.However,the relatively low strength had limited its application as a structural material.Owing to the rich reinforcing phase information and high performance,Mg-Zn-Y based magnesium alloy became the research focus in recent years.In this thesis,the high strain rates deformation behavior of Mg-3Zn-1Y magnesium alloy extrusion bar were investigated by the Split Hopkinson Pressure Bar（SHPB）.The X-ray analyses were applied to obtain the texture of different samples.AXIO HAL-100 Zeiss microscope was used to observe the initial and deformation microstructure.The effect of loading direction,strain rates and deformation temperature on the high strain rates deformation behavior of Mg-3Zn-1Y magnesium alloy were studied in this thesis.The high strain rates deformation mechanisms were analyzed on the microstructure observation.It was expected that the experimental results in the present paper could be a theoretical basis for the application of Mg-3Zn-1Y alloy in automotive,aerospace and other fields of impact-resistant occasions.The main results are as follows.The high strain rate compression tests along extrusion direction（ED）and extrusion radial direction（ERD）of Mg-3Zn-1Y magnesium alloy extruded bar were conducted with the strain rates ranging from 849s^-1-2915s^-1and at the temperature ranging from 20-300℃.The experimental results demonstrated that there was obvious anisotropy between ED and ERD samples.The ED samples had better mechanical properties than ERD samples.The anisotropic phenomenon between ED and ERD was much weaker when the temperature was much higher.Thermal softening effect played a key role during the high strain rate deformation when the temperature was involved.The dynamic compressive strength of extruded Mg-3Zn-1Y magnesium alloy gradually decreased,and the plastic deformation capacity was enhanced when the temperature was increasing.The results also demonstrated that the as-extruded Mg-3Zn-1Y magnesium alloy exhibiting pronounced anisotropy during compression.The anisotropy of the as-extruded Mg-3Zn-1Y magnesium alloy was arising from the variety of the deformation mechanisms.When the loading direction was along extrusion direction,the predominant deformation mode changed from extension twinning at a lower strain to prismatic slip at a higher strain.While compressed along extrusion radial direction,the predominant deformation mode changed from contraction twinning to a combination of basal and second order pyramidal slip with the increasing of strain.The dynamic compressive deformation mechanism at high temperatures of extruded Mg-3Zn-1Y magnesium alloy was a combination of slipping and twinning.Slipping is the main mechanism.During the dynamic deformation,recrystallization took place when the temperature was increased.