Study On Strengthening Mechanism Of Nano-diamonds Reinforced Magnesium Matrix Composite

Powder Metallurgy Process was used to prepare the magnesium matrix composites,thereinto,the ZK60 magnesium alloy was used as the matrix alloy,and as the Nano-diamond particles as the reinforcement.The microstructure evolution of the matrix and composite materials during the preparation processing was systematically studied,and the strengthening mechanism of the matrix and composite was analyzed in detail.The main content of this research are as follows: Firstly,the matrix alloy was prepared using different sintering methods.The effect of sintering temperature on the microstructure and mechanical properties of matrix alloy was studied and the optimal sintering method and sintering process parameters were determined.Then the matrix alloy was further prepared by the hot extrusion process.The effect of extrusion temperature on the microstructure and mechanical properties of matrix alloy was studied,and the optimal extrusion temperature was determined.Finally,tht composite was prepared by the method combining of vacuumhot press sintering and hot extrusion process.the effect of nano-diamond particle addition on the microstructure and mechanical properties of sintered and extruded composites was studied.The specific results of this study are as follows:The ZK60 magnesium alloy was prepared by vacuum hot pressing sintering in the temperature range of 450-600℃.When the sintering temperature was 450℃,the matrix alloy exhibited the best room temperature mechanical properties,and the yield strength,compressive strength and fracture strain reached to 135.1 MPa,342.0 MPa and 16.3%,respectively.The sintered alloy was further hot-extruded in the temperature range of 250-350℃.When the extrusion temperature was 250℃,the alloy exhibited the best microstructure and mechanical properties.The average grain size of the alloy was 2.50μm.The tensile yield strength,tensile strength and tensile fracture strain are 279 MPa,341 MPa and 18.1%,respectively,and the compressive yield strength,compressive strength and compressive fracture strain were 263 MPa,564 MPa and 13.8%,respectively.The value of tensile-compression yield asymmetry (CYS/TYS)is 0.94.When the ND addition amount is 0.25 wt%,the extruded composite displayed the best microstructure and mechanical properties.The average grain size of the material reduced to 1.70μm,and the tensile yield strength,tensile strength and tensile fracture strains were 320.6 MPa,344 MPa and 9.2%,respectively.The compressive yield strength,compressive strength and compressive fracture strain were 319.0 MPa,510.8 MPa and 16.6%,respectively,and the value of CYS/TYS increases to 0.99.When the extrusion temperature was 250 ℃,the microstructure evolution of ZK60 magnesium alloy was dominated by the continuous dynamic recrystallization and the twinning induced dynamic recrystallization,as well as forming comparatively weak <112 0>‖ED texture and the strong <101 0>‖ED texture characteristics.Based on the research results of the effects of grain size and precipitates on yield strength,the theoretical contributions of the two strengthening mechanisms were calculated to be 223.0 MPa and 113.6 MPa,respectively.For the composite materials,the strengthening mechanisms were mainly grain boundary strengthening mechanism,Orowan strengthening mechanism,thermal mismatch mechanism and load transfer mechanism.The theoretical contribution values of the four strengthening mechanisms of the 0.25ND/ZK60 composite were calculated to be 47.1 MPa,28 MPa,10.7 MPa and 0.35 MPa.