The Preparation Of Carbon-Nanotubes/AZ31 Magnesium Alloy Composites And ECAP Deformation

Carbon nanotubes(CNTs)/AZ31 magnesium composites have been casted by stirring casting method and adding precast block by plunger respectively,as-cast micro structure and mechanical properties were observed and tested respectively.And the composites produced by adding precast block by plunger were treated by solution treatment,and it's micro structure and mechanical properties were observed and tested.Fracture and Interface between CNTs and matrix were observed toward SEM and AFM.During producing composites by adding precast block by plunger,the dispersion of CNTs in precast block and AZ31 matrix were observed.In addition,the CNTs/AZ31 composites prepared by stirring casting method and adding precast block by plunger, were ECAPed on the state of Non pre-extruded and pre-extruded respectively, studying the ECAP deformation on the influence of the composites and mechanical properties of the composites after ECAP.It is showed that:CNTs/AZ31 composites prepared by adding precast block by plunger,where CNTs had a good dispersion in AZ31matrix,while there was a good dispersion in precast block.For the composites prepared by stirring casting method and adding precast block by plunger,as the addition of CNTs increased,grains were refined significantly and the mechanical properties were improved significantly.Tensile strength,micro-hardness and elongation all reached the maximum at the CNTs addtion of 1wt%.The maximum value of composite which was prepared by stirring casting was 190.3Mpa,88.6HVand 7.82% respectively,increased 27.9％,75.1% and 119.66% compared to the matrix;elastic mudulus reached the maximum of 90.86Gpa when the addtion of CNTs was 1.5wt%, increased 70.99% compared to the matrix.The CNTs/AZ31 composites produced by adding precast block by plunger,due to the good dispersion in matrix,the mechanical was better than the composites produced by stirring casting.The maximum value of tensile strength,micro-hardness and elongation was 210.3Mpa,96.6HVand 8.56% respectively,elastic mudulus reached the maximum of 98.88Gpa when the addtion of CNTs was 1.5wt%,;increased 10.5%,9.0%,9.5% and 8.8% respectively compared with the same addtion CNTs composites prepared by stirring casting;and after solution treatment,the tensile strength and elongation were all increased,and reached the maximum value of 230.2Mpa and11.32% respectively,increased 9.5% and 32.24% respectively compared with the as-cast composites;micro-hardness and elastic mudulus decresed compared wth the as-cast,and at the addition of CNTs of 1wt% and 1.5wt% reached the maximum value of 90.2 and 90.22 respectively ,decreased 6.6% and 8.76% respectively compared to the as-cast.1.0%wt CNTs/AZ31 composites which was produced by stirring casting,didn't be pre-extruded before ECAP deformation, after 1 pass, the samples were cracked remarkablely, the minimum grain size was about 5μm.Grain rotated, original grain orientation had been changed. Due to the addition of CNTs, texture emolliated.Micro-hardness increased significantly.after ECAP IP,the value of longitudinal section and cross-section was 110.6HV and 122.6HV respectively increased 46.5% and 62.4％respectively compared with the as-cast composites.1.0%wt CNTs/AZ31 composites which was produced by adding precast block by plunger,did be pre-extruded before ECAP deformation, after ECAP,casting defects decreased significantly,grain refined significantly;after ECAP 4 passes,grain size was refined to 2μm on average.tensile strength and elongation increased significantly,the maximum value was 306.3Mpa afte 1 pass and 23.33% after 4 passes respectively. After 4 passes, it appeared Non Hall-Petch phenomenon, which mainly because of grain-boundary sliding,texture emolliated and grain-boundary structure's combined action;and the main factors affect the composite's elongation after ECAP was the dispersion of CNTs in composites and the grain size of composites, both are combined role.The abruption form of CNTs/AZ31 magnesium composites on the state of as-cast and after solution treatment mainly was quasi-cleavage crack,which was made up of dimple and tear ridge. After ECAP deformation, the composites mainly were cracked as matrix ductile tear, tear ridge had a certain orientation,ductile rupture existed, the close area of CNTs mostly was sticky point with matrix and accompanied tracscrystalline fracture.There wasn't obvious interface reaction between CNTs and AZ31 matrix during the casting, and there was a strong interface bonding between CNTs and AZ31 matrix.