Research On The Thermal Deformation Cracking Behavior And Criterion Of As-cast AZ31B Magnesium Alloy

In recent years,magnesium alloy has been widely used in automobile industry,aerospace,medical,sporting goods,electronic products and other industries,as a kind of light alloy material with great potential.And many advantages such as light weight,high ratio of stiffness,good damping and good absorbing vibration ability,Anti-shielding electromagnetic interference and other properties are well reflected.However,the fracture phenomenon in the process of plastic deformation has become an important factor restricting its development.There will inevitably be surface cracking,edge cracks and other problems,whether through die-casting or rolling production of magnesium alloy products,and the more stringent deformation conditions,the more obvious this phenomenon..Therefore,in order to understand the thermal deformation cracking behavior and mechanism of magnesium alloys,and to predict the thermal deformation crack initiation of the alloy,the as-cast AZ31 B magnesium alloy is selected as the research object in this paper.And the thermal deformation cracking behavior and cracking mechanism of magnesium alloy is studied by use of Gleeble Thermal simulation compression test,finite element simulation and high speed photographic technique,and meanwhile,the thermal deformation cracking criterion of magnesium alloy considering temperature and strain rate is established.The details are as follows:Through the flow stress-strain curve of AZ31 B magnesium alloy,the rheological behavior of the alloy was analyzed,and the constitutive model under different thermal deformation conditions was established.Then,the thermal process diagram of the alloy was drawn by the dynamic material model,and the rheological instability of the alloy was analyzed.The cracking mode was investigated based on the thermal deformation of the magnesium alloy specimens by means of high-speed photography,metallographic,fracture and EDS and other detective technologies.and the results showed that the thermal deformation of the alloy mainly was 45° shear cracking,which could be divided into the unidirectional 45°,the crossed 45°,the parallel 45° and the hyrid 45° shear cracking.Moreover,the presence of precipitates in the structure affected the hot compressive deformation cracking of the AZ31 B magnesium alloy.The position of the crack on the surface of the alloy specimen was accurately captured based on recording and analyzing the thermal compression process of the alloy by means of high speed photography,and the critical cracking deformation of the material was accurately measured,which increased with the increase of the deformation temperature and the strain rate,and showed good regularity.The stress-strain and damage evolution of the alloy during thermal deformation were numerically simulated with the DEFORM-3D finite element simulation software.The results showed that the cracking behavior of AZ31 B magnesium alloy in the thermal compression deformation could been characterized very well by the Frudenthal criterion,which could predict the initial cracking point of the forming process successfully.Then,the thermal deformation cracking criterion considering the thermal deformation parameters,such as stress,strain,strain rate and deformation temperature,was established.