碳纳米管/AZ31镁基复合材料的制备及ECAP变形
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摘要
采用机械搅拌法及钟罩浸块铸造法(制取预制块后压块浸渗的两步方法)分别制备了CNTs/AZ31镁基复合材料,对其铸态组织及力学性能分别进行了观察及测试,且对采用钟罩浸块法制备的复合材料进行了固溶处理,并对其组织及力学性能分别进行了观察及测试,并对各种状态下的材料的断口形貌及CNTs与基体的界面结合问题进行了SEM(扫描电镜)和AFM(原子力显微镜)观察。在钟罩浸块法制备复合材料过程中,还对CNTs在预制块及基体中的分散性进行了SEM观察。此外,本文还对机械搅拌法和钟罩浸块法制备的CNTs/AZ31镁基复合材料分别进行了未预挤压态及预挤压态的ECAP(等通道转角挤压)变形,研究ECAP变形对复合材料组织及力学性能的影响。
研究结果表明：采用钟罩浸块法制备CNTs/AZ31镁基复合材料,CNTs在预制块及AZ31基体中具有较好的分散程度。对于机械搅拌法及钟罩浸块法制备的CNTs/AZ31镁基复合材料,随着CNTs加入量的增加,晶粒都明显细化,力学性能都明显提高。抗拉强度、显微硬度和延伸率都在CNTs加入量为1wt%时达到最大值。机械搅拌法制备的分别为190.3Mpa、88.6HV和7.82%,相比AZ31合金分别提高了27.9%、75.1%和119.66%；弹性模量在CNTs加入量为1.5%wt时达到最大值90.86Gpa,相比基体提高了70.99%。钟罩浸块法制备的CNTs/AZ31镁基复合材料,相比机械搅拌法,由于CNTs在复合材料中的良好分散性,导致力学性能较之提高。抗拉强度、显微硬度、延伸率的最大值分别为210.3Mpa、96.6HV和8.56%,弹性模量在CNTs加入量为1.5wt%时达到最大值98.88Gpa;相比机械搅拌法制备的相同CNTs含量材料,分别提高了10.5%、9.0%、9.5%和8.8%；且经过固溶处理后,抗拉强度和延伸率都明显提高,在CNTs加入量为1wt%时分别达到最大值230.2Mpa和11.32%,相比铸态时,分别提高了9.5%和32.24%；显微硬度和弹性模量相对铸态都有所降低,在CNTs加入量为1wt%和1.5wt%时分别达到最大值90.2和90.22,相比铸态时,分别降低了6.6%和8.76%。
未预挤压态的机械搅拌法制备的1%wtCNTs/AZ31镁基复合材料ECAP变形一道次后,试样开裂明显,复合材料最小晶粒尺寸达到约5μm。晶粒发生转动,原有的晶粒取向被改变,由于CNTs的加入,有织构软化的倾向。显微维氏硬度显著提高；经ECAP变形一道次后,纵截面和横截面显微硬度值为110.6和122.6HV,分别提高了46.5%和62.4%。
预挤压态的钟罩浸块法制备的1%wtCNTs/AZ31镁基复合材料ECAP变形后,试样的铸造缺陷大大减小,晶粒得到明显细化；经过ECAP变形四道次后,晶粒尺寸细化显著,平均约为2μm,抗拉强度和延伸率显著提高,最大值分别为1道次后的306.3Mpa及四道次后的23.33%。ECAP变形四道次后,抗拉强度与晶粒的尺寸出现反Hall-Petch现象,主要是因为晶界滑动、织构弱化以及晶界结构综合作用的结果；影响ECAP后复合材料的延伸率变化的主要因素为CNTs的分散程度以及复合材料的晶粒尺寸,两者综合作用。
铸态及固溶处理后的CNTs/AZ31镁基复合材料的断裂形式主要都为准解理断裂,由韧窝和撕裂棱所组成。ECAP变形后,复合材料以基体延性撕裂为主体,撕裂棱具有一定取向性,存在韧性断裂带,CNTs密集区域多数为CNTs/基体界面脱粘并伴随穿晶断裂的形式。CNTs与AZ31基体间在铸造复合过程中无明显的界面反应,且与基体界面结合紧密。
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.
研究结果表明：采用钟罩浸块法制备CNTs/AZ31镁基复合材料,CNTs在预制块及AZ31基体中具有较好的分散程度。对于机械搅拌法及钟罩浸块法制备的CNTs/AZ31镁基复合材料,随着CNTs加入量的增加,晶粒都明显细化,力学性能都明显提高。抗拉强度、显微硬度和延伸率都在CNTs加入量为1wt%时达到最大值。机械搅拌法制备的分别为190.3Mpa、88.6HV和7.82%,相比AZ31合金分别提高了27.9%、75.1%和119.66%；弹性模量在CNTs加入量为1.5%wt时达到最大值90.86Gpa,相比基体提高了70.99%。钟罩浸块法制备的CNTs/AZ31镁基复合材料,相比机械搅拌法,由于CNTs在复合材料中的良好分散性,导致力学性能较之提高。抗拉强度、显微硬度、延伸率的最大值分别为210.3Mpa、96.6HV和8.56%,弹性模量在CNTs加入量为1.5wt%时达到最大值98.88Gpa;相比机械搅拌法制备的相同CNTs含量材料,分别提高了10.5%、9.0%、9.5%和8.8%；且经过固溶处理后,抗拉强度和延伸率都明显提高,在CNTs加入量为1wt%时分别达到最大值230.2Mpa和11.32%,相比铸态时,分别提高了9.5%和32.24%；显微硬度和弹性模量相对铸态都有所降低,在CNTs加入量为1wt%和1.5wt%时分别达到最大值90.2和90.22,相比铸态时,分别降低了6.6%和8.76%。
未预挤压态的机械搅拌法制备的1%wtCNTs/AZ31镁基复合材料ECAP变形一道次后,试样开裂明显,复合材料最小晶粒尺寸达到约5μm。晶粒发生转动,原有的晶粒取向被改变,由于CNTs的加入,有织构软化的倾向。显微维氏硬度显著提高；经ECAP变形一道次后,纵截面和横截面显微硬度值为110.6和122.6HV,分别提高了46.5%和62.4%。
预挤压态的钟罩浸块法制备的1%wtCNTs/AZ31镁基复合材料ECAP变形后,试样的铸造缺陷大大减小,晶粒得到明显细化；经过ECAP变形四道次后,晶粒尺寸细化显著,平均约为2μm,抗拉强度和延伸率显著提高,最大值分别为1道次后的306.3Mpa及四道次后的23.33%。ECAP变形四道次后,抗拉强度与晶粒的尺寸出现反Hall-Petch现象,主要是因为晶界滑动、织构弱化以及晶界结构综合作用的结果；影响ECAP后复合材料的延伸率变化的主要因素为CNTs的分散程度以及复合材料的晶粒尺寸,两者综合作用。
铸态及固溶处理后的CNTs/AZ31镁基复合材料的断裂形式主要都为准解理断裂,由韧窝和撕裂棱所组成。ECAP变形后,复合材料以基体延性撕裂为主体,撕裂棱具有一定取向性,存在韧性断裂带,CNTs密集区域多数为CNTs/基体界面脱粘并伴随穿晶断裂的形式。CNTs与AZ31基体间在铸造复合过程中无明显的界面反应,且与基体界面结合紧密。
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.
引文
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