The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield stren...The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield strength, tensile strength and elongation of the joints 17 520 h natural aging were about 20%, 12% and 24% higher than those joints natural aging 72 h. Hardness profile of natural aging 17 520 h joint witnessed significant enhancement in nugget zone, compared with 72 h natural aging. Differential scanning calorimetry （ DSC ） and transmission electron microscopy （TEM） test revealed that more Guinier-Preston zone, η＇ and 71 phase emerged in nugget zone as natural aging duration increased, high density of dislocation located within grain boundary in nugget zone of joints natural aging 72 h. It is concluded that natural aging was feasible to enhalwe strength and plasticity of FSW joints simultaneously.展开更多
The molecular structures,molecular weights,viscocities and moduli of thermal aged and thermal oxidative aged epoxidized natural rubber（ENR） were determined by means of FTIR,GPC and RPA.It was found that the decrease...The molecular structures,molecular weights,viscocities and moduli of thermal aged and thermal oxidative aged epoxidized natural rubber（ENR） were determined by means of FTIR,GPC and RPA.It was found that the decrease in the IR absorption intensity of the epoxy was more obvious than that of the C[ZJLX,Y]C bond,and the molecular weight and the dynamic rheological behavior had changed.Mn and Mw were reduced respectively by 26% and 5% after thermal oxidative aging.After thermal aging,however,Mn was reduced by 2% only,and Mw increased by 6%.The molecular weight distribution broadened from 3.18 for ENR to 3.43 for the thermal aged ENR and 4.05 for the thermal oxidative aged ENR.The decrement of η* of the thermal aged ENR with rising shear rate was larger than that of the unaged ENR,but for the thermal oxidative ENR the decrement of η* was lower compared with the unaged ENR.G′ of the thermal aged ENR decreased slightly and G′ of the thermal oxidative aged ENR was obvious lower than that of the unaged ENR in the low frequency range.In the high frequency range,G′ of the thermal aged ENR was larger than that of the unaged ENR,and G′ of the thermal oxidative ENR increased to the same level as that of the unaged ENR.展开更多
Variable masses of nano cerium oxide (CeO2) were added into nano silica (SiO2) to prepare the well-dispersed SiO2-CeO2 suspension (SiO2-CeO2), cetyltrimethyl ammonium bromide (CTAB) was used to adjust the compatibilit...Variable masses of nano cerium oxide (CeO2) were added into nano silica (SiO2) to prepare the well-dispersed SiO2-CeO2 suspension (SiO2-CeO2), cetyltrimethyl ammonium bromide (CTAB) was used to adjust the compatibility of SiO2-CeO2 with rubber matrix, then SiO2-CeO2 modified by CTAB and curing formulas were mixed with fresh natural rubber (NR) latex to prepare NR/SiO2-CeO2 nanocomposites that contained 0–10 parts of CeO2 by a new emulsion compounding method. The morphologies, cure characteristics, mechanical properties and thermal-oxidative stability of NR/SiO2-CeO2 nanocomposites were investigated. The re-sults revealed that the presence of CeO2 in NR/SiO2-CeO2nanocomposites was favorable for enhancing the interaction between NR matrix and fillers, helped to get smaller SiO2-CeO2 particles with narrower particle size distribution, further improved the crosslink densities and mechanical properties of NR/SiO2-CeO2 nanocomposites vulcanizates. Meanwhile, the addition of CeO2 increased the active energy at least 4.66%, obviously improved the thermal-oxidative aging-inhibiting properties of NR/SiO2-CeO2 nanocomposites. Additionally, nanocomposites containing CeO2 promotedTg shift to high temperature direction, causing the nanocomposites featured higher tanδ at 0 oC and lower tanδ at 60 oC and exhibited comparable wet grip and lower rolling resistance when NR/SiO2-CeO2nano-composites were used in tire tread compound.展开更多
文摘The microstructure and mechanical properties of friction stir welded 2. 5 mm 7050-T7451 aluminum alloy natural aging 72 h and 17 520 h were investigated, respectively. The uniaxial tensile test showed that yield strength, tensile strength and elongation of the joints 17 520 h natural aging were about 20%, 12% and 24% higher than those joints natural aging 72 h. Hardness profile of natural aging 17 520 h joint witnessed significant enhancement in nugget zone, compared with 72 h natural aging. Differential scanning calorimetry （ DSC ） and transmission electron microscopy （TEM） test revealed that more Guinier-Preston zone, η＇ and 71 phase emerged in nugget zone as natural aging duration increased, high density of dislocation located within grain boundary in nugget zone of joints natural aging 72 h. It is concluded that natural aging was feasible to enhalwe strength and plasticity of FSW joints simultaneously.
文摘The molecular structures,molecular weights,viscocities and moduli of thermal aged and thermal oxidative aged epoxidized natural rubber（ENR） were determined by means of FTIR,GPC and RPA.It was found that the decrease in the IR absorption intensity of the epoxy was more obvious than that of the C[ZJLX,Y]C bond,and the molecular weight and the dynamic rheological behavior had changed.Mn and Mw were reduced respectively by 26% and 5% after thermal oxidative aging.After thermal aging,however,Mn was reduced by 2% only,and Mw increased by 6%.The molecular weight distribution broadened from 3.18 for ENR to 3.43 for the thermal aged ENR and 4.05 for the thermal oxidative aged ENR.The decrement of η* of the thermal aged ENR with rising shear rate was larger than that of the unaged ENR,but for the thermal oxidative ENR the decrement of η* was lower compared with the unaged ENR.G′ of the thermal aged ENR decreased slightly and G′ of the thermal oxidative aged ENR was obvious lower than that of the unaged ENR in the low frequency range.In the high frequency range,G′ of the thermal aged ENR was larger than that of the unaged ENR,and G′ of the thermal oxidative ENR increased to the same level as that of the unaged ENR.
基金supported by the Special Fund for Agro-scientific Research in the Public Interest,Ministry of Agriculture of the People’s Republic of China(201403066)Natural Science Foundation of Hainan Province(20155198)the Fundamental Research Funds for Rubber Research Institute,Chinese Academy of Tropical Agricultural Science(1630022014014)
文摘Variable masses of nano cerium oxide (CeO2) were added into nano silica (SiO2) to prepare the well-dispersed SiO2-CeO2 suspension (SiO2-CeO2), cetyltrimethyl ammonium bromide (CTAB) was used to adjust the compatibility of SiO2-CeO2 with rubber matrix, then SiO2-CeO2 modified by CTAB and curing formulas were mixed with fresh natural rubber (NR) latex to prepare NR/SiO2-CeO2 nanocomposites that contained 0–10 parts of CeO2 by a new emulsion compounding method. The morphologies, cure characteristics, mechanical properties and thermal-oxidative stability of NR/SiO2-CeO2 nanocomposites were investigated. The re-sults revealed that the presence of CeO2 in NR/SiO2-CeO2nanocomposites was favorable for enhancing the interaction between NR matrix and fillers, helped to get smaller SiO2-CeO2 particles with narrower particle size distribution, further improved the crosslink densities and mechanical properties of NR/SiO2-CeO2 nanocomposites vulcanizates. Meanwhile, the addition of CeO2 increased the active energy at least 4.66%, obviously improved the thermal-oxidative aging-inhibiting properties of NR/SiO2-CeO2 nanocomposites. Additionally, nanocomposites containing CeO2 promotedTg shift to high temperature direction, causing the nanocomposites featured higher tanδ at 0 oC and lower tanδ at 60 oC and exhibited comparable wet grip and lower rolling resistance when NR/SiO2-CeO2nano-composites were used in tire tread compound.
