Study On Dynamic Mechanical Behavior And FEM On Ballistic Resistance Properties Of 7A52 Aluminum Alloy Weld Joint

The main connection method of armored aluminum alloy is welding.As a weak link,the performance of welded joint is an important factor affecting the overall protective performance of armored vehicles.This paper takes 7A52 aluminum alloy MIG welding joint(ER5356 aluminum alloy as welding wire)as the research object.The dynamic mechanical behavior and microstructure evolution of 7A52 aluminum alloy welded joints were studied through SHPB test,combined with OM,TEM and other microstructure analysis methods.The J-C constitutive equation of welded joint is established.The armor penetration process of welded joint is analyzed by finite element simulation.The viewpoints and results were enumerated as followings:(1)The effects of temperature and strain rate on the macroscopic deformation behavior of 7A52 aluminum alloy weld,base metal and joint are studied.It is found that the deformation degree of weld,base metal and joint increases with the increase of strain rate.Due to the great plasticity of the weld,there are no cracks on the surface and only upsetting deformation are founded in the entire strain range.When the strain rate increases from 2600s-1 to 4600s-1,a "V" shaped crack occurs in the base metal,and obvious uneven deformation occurs at the junction between the base metal and the weld.When the impact temperature increased from-80℃ to 300℃,the deformation behaviors of the weld,base metal and joint gradually tended to be uniform.(2)The effects of strain rate and temperature on the microstructural deformation behavior of welds,base metal and joints were investigated.With the increase of the strain rate,the grains in the deformation zone in the middle of the weld are elongated.while the microstructure of the base metal is first twisted and deformed,followed by DSB,then by TSB,and finally cracked.When the impact temperature gradually increases,the area of the deformation zone in the middle of the weld has expanded,and the grains are further elongated;the η’ phase in the base metal is transformed into the η phase.When the impact temperature is higher than 200 °C,the main performance of structure is deformation band.For the joint,ASB is only generated near the zone of fusion and the base metal when the impact temperature is below 200°C.(3)The dynamic mechanical behavior of weld,base metal and joint is studied,and the constitutive model of weld and base metal is established.Improvement of the strain rate and decrease with the increase of temperature is clarified to be more beneficial to dynamic yield stress,flow stress,energy absorption and adiabatic temperature rise of weld,base metal and joint increase.The predicted results of the established constitutive model are almost the same as the experimental results,and the prediction accuracy of the constitutive model is high.(4)The finite element model of the bullet penetrating the welded joint is established,and the penetration trajectory of the bullet is analyzed according to the force of the bullet in the penetration process.When the bullet penetrates the weld of the welding plate obliquely,it will be subjected to asymmetric stress,which causes the incident inclination of the bullet to change,and as the penetration progresses,the incident inclination first increases and then decreases.The simulation results are in good agreement with the experimental results.