Investigation On The Mechanical Behavior And Mechanism Of Mg₂B₂O₅w/ND Reinforced Magnesium Matrix Composites

The requirements of light and efficient materials are increasing in aerospace,aviation and automobile industries,with the increasing demand for energy conservation and environmental pollution reduction.Therefore,it is urgently to develop high performance,low cost and lightweight magnesium matrix composites.In this paper,ultra-fine ZK60 magnesium alloy,ND/ZK60,Mg₂B₂O₅w/ZK60 and?0.05wt%ND+7wt%Mg2B2O5w?/ZK60magnesiummatrixcompositewere successfully fabricated by powder metallurgy.Tensile-pressure properties were tested by using Instron-5982 universal testing machine in the room temperature,X-ray diffraction?XRD?,SEM,TEM,EDS and EBSD were used to observe and analyze the microstructure of the materials.The relation between microstructure and mechanical properties of ultra-fine ZK60 magnesium alloy was studied at different extrusion temperature.The results showed that MgZn₂ particles were uniformly distributed in the Mg matrix,the texture of?0002?basal was gradually weakened,and the tension-compression asymmetry decreased,as the extrusion temperature elevate.When the extrusion temperature increased from 523 K to 623 K,the full dynamic recrystallization replaced part dynamic recrystallization,and the average grain size increased from 0.715?m to 1.36?m.Under the extrusion temperature 523 K,samples showed excellent mechanical properties,the tensile yield strength,tensile fracture strength,compression yield strength and compression fracture strength,were 386.9 MPa,421.6 MPa,359 MPa and 523 MPa,respectly.The high strength of alloy is mainly attributed to grain refinement and dispersion strengthening of MgZn₂ particles.The study on the microstructure of ND/ZK60 magnesium matrix composites found that 0.05wt%ND was evenly distributed in the matrix,as well as precipitated nano-MgZn₂ phases throughout the composite matrix.Compared with ZK60 alloy,the composite with only 0.05wt%ND can perform 15.1%and 44.3%enhancement in tension and compression yield strength up to 390.3 MPa and 433 MPa,exhibiting an ultra-high strengthening efficiency of tension yield strength?St?and compressive yield strength?Sc?are 302 and 887,respectively.At the same times,the composite keeps good tensile and compressive yield symmetry.Based on theoretical analysis,the high strength of the composite is mainly attributed to thermal mismatch strengthening,grain refinement,Orowan strengthening.The researches of microstructure of the Mg₂B₂O₅w/ZK60 composites found that as the whisker content 7wt%,whisker was uniformly distributed in the matrix,interface bonding of whisker and matrix is good,and it has good comprehensive mechanical properties,tensile yield strength,tensile fracture strength,compression yield strength and compression fracture strength were 383.8 MPa,418.7 MPa,421MPa and 463 MPa,respectly.The high strength of composite is mainly attributed to fine grain strengthening and the enhancement of the load transfer.As the content of whisker was increased to 9wt%and 15wt%,the whisker occurs partially reunite,resulting in performance of composite materials deteriorates.Through the study of?0.05wt%ND+7wt%Mg₂B₂O₅w?/ZK60 magnesium matrix composite,it was found that ND and Mg₂B₂O₅w were evenly distributed in the matrix,and the MgZn₂ particles uniformly distributed in the grain boundary.The initial state of composite material had weakly?0002?basal fiber texture.In the process of tensile-pressure deformation,there is no obvious change in the base texture of composite material.At the same times,the composite also shows good comprehensive mechanical properties,the tensile yield strength,ultimate tensile strength and elongation ratio were 407.6 MPa,459.3 MPa and 6.2%,respectively,compression yield strength,ultimate compression strength and compression ratio were 459.0 MPa,488.2 MPa and 3.7%,respectively.