Study On Dynamic Compression Properties And Deformation Mechanism Of ZC61 Alloy Under Dynamic Loading

Magnesium alloys of high strength and high elastic modulus with good shock absorption properties have emerged as potential alternatives to heavier alloys for automotive parts.As a key material used in light-weight vehicles,magnesium alloys are often subjected to high strain rate loading,which leads to the mechanical behavior and deformation mechanism differences of the alloy compared to quasi-static loading.Therefore,it is necessary to investigate their deformation mechanism under high strain rate.In this study,Mg-6Zn-1Cu-0.6Zr(ZC61)alloy was fabricated using a novel extrusion-shearing process that combines traditional hot extrusion with equal-channel angular pressing(ECAP).The dynamic compression mechanical properties of the alloy were studied using the split Hopkinson pressure bar(SHPB)along the extrusion area,corner area and forming area extrusion direction(ED)and extrusion radius direction(ERD)in the range of strain rate of 1100 s^-1?2200 s^-1.The microstructural evolution and fracture mechanism were analyzed by optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction analysis(XRD),backscattered electron analysis(EBSD)and transmission electron microscope(TEM).The experimental results show that ZC61 alloy is mainly composed of?-Mg matrix,MgZn Cu phase and MgZn₂ phase.After extrusion shearing,the alloy occurs complete dynamic recrystallization,and the grains size are significantly refined.The average grain sizes are refined from 4.45?m in the extrusion area to 2.61?m in the forming area.The{0001}basal texture is produced in the forming area,which causes strong anisotropy under dynamic loading below 250?.Dynamic compression experimental results show that the ED and ERD samples exhibit a positive strain rate strengthening effect.At a strain rate of 2200s^-1,the ultimate compressive strength of ED and ERD samples reached to 581 MPa and 530MPa,respectively.Meanwhile,by the analysis of the fracture surfaces and the calculation results of energy absorption density and temperature rise,it can be known that the fracture mechanism of the alloy ED sample is brittle fracture and local melting,while the ERD sample shows brittle fracture.Under high strain rate loading at room temperature,the deformation mechanism of extrusion area and forming area is main extension twinning.The main deformation mode of the corner area is the migration of subgrain boundaries caused by dislocation slip.With the increment of loading temperature,{1122}<23>second order pyramidal slip and{1011}-{1012}secondary twinning also accommodate the deformation of the samples in the extrusion area and the forming area,respectively.The migration of subgrain boundaries caused by dislocation slip is still the main deformation mode in the corner area.