In-situ Observation Of Microcrack Propagation Behavior Of Magnesium Alloy

With the advancement of science and technology,the performance aspect of aerospace equipment is rapidly developing in the direction of long life,large size,high load capacity and light weight.Because magnesium alloys have high specific strength,high specific stiffness and excellent damping properties,some components of aerospace equipment are gradually using high-performance magnesium alloys instead of other traditional materials such as iron and aluminum.In the traditional method,the plastic deformation behavior and fracture behavior of magnesium alloy are mainly analyzed by thermal simulation and room temperature tensile test.But the microstructure change of the material during the experiment is difficult to see.So it lacks of direct evidence of plastic deformation behavior and fracture behavior.In-situ loading technique can be used to track the microstructure changes and damage process of the surface of the experimental material in real time,so as to deeply understand the plastic deformation and cracking damage of the material.This will provide the most direct evidence for evaluating and improving the macro and micro characteristics of materials.In this paper,AZ31 magnesium alloy and Mg-13Gd-4Y-2Zn-0.5Zr deformed rare earth magnesium alloy were selected as research materials.Microscopic characterizations are studied by DSC analysis,metallographic microstructure observation,and Image-pro Plus software analysis.Mechanical properties of magnesium alloys were tested by hardness testing.The crack initiation and propagation behavior of annealed AZ31 magnesium alloy and solid solution rare earth magnesium alloy were studied by scanning electron microscopy-in-situ loading method.The specific conclusions are:(1)During the deformation process of the annealed AZ31 magnesium alloy,The grain that has activated the slip system exerts a force on the grain that has not activated the slipsystem.The slip line on the surface of the deforming grain reaches the grain boundary and causes stress concentration at the grain boundary.The microcrack appears in grain boundaries and expands according to the microcrack-large crack-intergranular crack.(2)After the different solution treatment process,the second phase in the Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy still remains,and is dominated by the bulk phases.The influence of solution temperature on the second phase is more obvious than the solution time.(3)When the solution treatment process is 480°C×10h and 510°C×10h,most of the bulk LPSO phase remains on the surface of the Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy matrix.Because the elastic modulus of the bulk LPSO phase is much higher than the elastic modulus of the matrix,and the stress of the matrix gradually shifts to the bulk LPSO phase during the tensilie process,so that the stress concentration on the bulk LPSO phase leads to the generation of cracks.(4)When the solution treatment process is 510°C×13 h and 510°C×16h,the structure of the bulk LPSO phase is changed during the solution treatment,the resistance to dislocation slip is enhanced,and the LPSO/?-Mg interface is cracked.(5)When the solution treatment process is 510°C×19h,510°C×22h,the increase of heating time leads to growth of grains in the Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy,which lead to the increase of dislocation slip distance.Then it causes the dislocation accumulation energy is too high,and the force on the grain boundary is too large to appear the crack at the grain boundary.(6)When the solution treatment process is 510°C×16h,the stress of producing the first crack and fracture strength of the Mg-13Gd-4Y-2Zn-0.5Zr rare earth magnesium alloy are the largest,and the crack defects are the least.Therefore,510°C×16h is the best solution treatment process.