The Fracture Behavior Of AZ31B Magnesium Alloy And Its Weld Joint Based On Acoustic Emission

As a new structural material,magnesium has been applied into many fields including the automobile,high-speed train,aerospace and other traffic transport structures.However,the performance of the connected joint becomes a limitation to the service life of the material.The electronic beam welding was adopted because of the small heat affected zone and less deformation of the weld joint,which improved the mechanical traits.The structural material suffered from cyclic load,so the fatigue fracture is a common broken way,which is of great significance to the fatigue research.For the crack propagates quickly after the initiation,a precise and potent method was necessary,and the acoustic emission technology has merits of convenience,real-time monitoring and high precision.It was able to collect the signals and then provide a relationship between the energy dissipation and the deformation mechanisms.So,the fatigue crack behavior was detected by the acoustic emission method in current study.The fatigue crack propagation behavior of the AZ31 B magnesium and its weld seam were monitored by acoustic emission technology.Combined with the microstructural analyze,the relationship between the deformation and the acoustic signals was revealed.Acoustic emission method could evaluate the damage of the specimen and predict the remaining service life.The results demonstrated that the acoustic emission technology could locate the crack source of the AZ31 B magnesium.Analyzation of the acoustic emission data and the results of the material texture proved that the acoustic emission method is a potent approach to investigate the magnesium deformation.The deformation mechanisms could be obtained via different properties of the acoustic signals.For instance,it could distinguish the slip and twin according to the frequency of the signals: the frequency of slip and twin signal is 140 kHz and 250 kHz respectively.This result has significant meaning to the latter research.The fatigue crack propagation behavior of AZ31 B is studied by the acoustic method,and the C-a curve showed a power function which could calculate the crack length on the basis of the counts,and then gain the stress intensity factor range,so the remaining life of the specimen could be received.It is tested that the crack along with the RD direction propagates faster than that of the other direction by comparing the acoustic parameters.This is a rational result for the crack propagation of the TD direction produced more twins and the grains getting smaller,which could deny the growth of the crack.So the fracture performance of the magnesium in ED direction is super than that of the RD direction.There is no brittle compound in AZ31 B magnesium electronic beam weld,and the cracking progress could be divided into two stages according to acoustic curves: the stable cracking stage and the unstable cracking stage,and there are clear cleavage steps in the stable cracking stage,while the dimples appeared gradually on the fracture surface.The crystals near the crack margin have been studied by Electron Back-Scattered Diffraction method,which demonstrated that the grains with small schmid factor have negative effect on the crack propagation of AZ31 B magnesium.Attributed of these of advantages,the acoustic emission method is significant to the research of the magnesium,especially in the damage detection.