5083 Al alloy sheets with different grain sizes(8.7-79.2 μm) were obtained by cold rolling and annealing. Their microstructures, intergranular corrosion(IGC), stress corrosion cracking(SCC), and crack propagation beh...5083 Al alloy sheets with different grain sizes(8.7-79.2 μm) were obtained by cold rolling and annealing. Their microstructures, intergranular corrosion(IGC), stress corrosion cracking(SCC), and crack propagation behaviors were investigated. The results showed that samples with coarse grains exhibit better IGC resistance with a corrosion depth of 15 μm. The slow strain rate test results revealed that fine-grained samples exhibit better SCC resistance with a susceptibility index(ISSRT) of 11.2%. Furthermore, based on the crack propagation mechanism, grain refinement can improve the SCC resistance by increasing the number of grain boundaries to induce the corrosion crack propagation along a tortuous path. The grains with {011} orientation could hinder crack propagation by orientating it toward the low-angle grain boundary region. The crack in the fine-grained material slowly propagates due to the tortuous path, and low H;and Cl;concentrations.展开更多
The effect of transition elements on grain refinement of 7475 aluminum alloy sheets produced by warm rolling was investigated. The alloy which contains zirconium instead of chromium showed ultra fine structures with s...The effect of transition elements on grain refinement of 7475 aluminum alloy sheets produced by warm rolling was investigated. The alloy which contains zirconium instead of chromium showed ultra fine structures with stable subgrains after warm rolling at 350 ℃, followed by solution heat treatment at 480 ℃. The average subgrain diameter was approximately 3 pan. It became clear that zirconium in solution has the effect of stabilizing subgrains due to precipitation of fine Al3Zr compounds during warm rolling. On the other hand, chromium-bearing compounds precipitate before warm rolling and they grow up to relatively large size during warm rolling. The warm rolled sheets with fine subgrains have unique properties compared with conventional 7475 aluminum alloy sheets produced by cold rolling. The warm roiled sheets solution heat treated had subgrain structures through the thickness with a high proportion of low-angle boundary less than 15°. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional 7475 aluminum alloy sheets. As the most remarkable point in the warm rolled sheets, the high Lankford （r） value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed r-fiber textures, especially with the strong {011 }（211） brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low- angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.展开更多
Metallurgical and mechanical properties along with shape memory and corrosion behavior of Cu-11.8% AI-3.7% Ni-1 %Mn and Cu-11% A1 5.6% Mn shape memory alloys （SMAs） were comparatively studied. The influence of grain...Metallurgical and mechanical properties along with shape memory and corrosion behavior of Cu-11.8% AI-3.7% Ni-1 %Mn and Cu-11% A1 5.6% Mn shape memory alloys （SMAs） were comparatively studied. The influence of grain refinement on the properties was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC）, potentiodynamic polarizations and bend and tensile tests. Static recrystallization and kinetic grain growth show a rapid recrystallization in the first 15 s of annealing at 800℃ followed by grain growths. The minimum grain sizes obtained after 15 s are 90 and 260 μm for Cu-A1-Ni-Mn and Cu-A1-Mn, respectively. Tensile tests show typical three-stage curves for both alloys, and it is seen that alloys exhibit high fracture stress and strain after grain refinement. Microstructural observations show zig-zag morphology of β 1martensite in the Cu-A1-Ni-Mn and coexistence of β1 and y1 in the Cu-A1-Mn, which were confirmed by differential scanning calorimetry results. The shape memory ratios （17） of the alloys before thermomechanieal treatment, and after thermomechanical annealing at 800 ℃ for different time up to 15 min followed by water quenching, were evaluated. In addition, corrosion behavior of alloys after grain refinement was analyzed by means of potentiodynamic polarization measurements. The results showed that the anodic reactions were dominated by dissolution of copper, and Cu-AI-Ni-Mn alloy exhibits a better corrosion resistance than Cu-A1-Mn alloy.展开更多
Friction stir extrusion(FSE)is known as an innovative manufacturing technology that makes it possible to directly produce wire via consolidation and extrusion of metal chips or solid billets.In this study,wire samples...Friction stir extrusion(FSE)is known as an innovative manufacturing technology that makes it possible to directly produce wire via consolidation and extrusion of metal chips or solid billets.In this study,wire samples were produced using aluminum alloy AA7022 machining chips by the use of the FSE.To this end,the microstructures and mechanical properties of the base material(BM)and the extruded samples were investigated.The corrosion resistance of the given samples was also determined using potentiodynamic polarization technique.The results showed that the samples manufactured at higher rotational speeds possessed good surface quality,the process temperature and the grain size similarly increased following the rise in rotational speed,and the mechanical properties consequently decreased.Using the FSE led to crystallite refinement,increase in volume fraction of grain boundaries,as well as re-distribution of precipitates affecting corrosion resistance.Furthermore,the findings of the corrosion tests revealed that the produced samples by the FSE had adequate corrosion resistance and the growth in die rotation rate augmented current density and subsequently reduced corrosion resistance.展开更多
The corrosion properties of pure zirconium(Zr)with different grain sizes in acid,alkali,and salt environments were studied.The microstructures of pure Zr were observed by optical microscope,X-ray diffractometer,and el...The corrosion properties of pure zirconium(Zr)with different grain sizes in acid,alkali,and salt environments were studied.The microstructures of pure Zr were observed by optical microscope,X-ray diffractometer,and electron backscattered diffraction probe.The corrosion resistance of pure Zr was analyzed by electrochemical corrosion test and immersion test.Results show that pure Zr with grain size of 4–32μm can be obtained after annealing at 800°C for different durations,and the relationship between grain size and annealing duration is D^(3)−D_(0)^(3)=3.35t.The electrochemical corrosion and immersion corrosion test results show that the pure Zr with grain size of about 24μm(annealing at 800°C for 20 h)possesses the optimal corrosion resistance.展开更多
基金financial support and Program of the Ministry of Education in China (2011)。
文摘5083 Al alloy sheets with different grain sizes(8.7-79.2 μm) were obtained by cold rolling and annealing. Their microstructures, intergranular corrosion(IGC), stress corrosion cracking(SCC), and crack propagation behaviors were investigated. The results showed that samples with coarse grains exhibit better IGC resistance with a corrosion depth of 15 μm. The slow strain rate test results revealed that fine-grained samples exhibit better SCC resistance with a susceptibility index(ISSRT) of 11.2%. Furthermore, based on the crack propagation mechanism, grain refinement can improve the SCC resistance by increasing the number of grain boundaries to induce the corrosion crack propagation along a tortuous path. The grains with {011} orientation could hinder crack propagation by orientating it toward the low-angle grain boundary region. The crack in the fine-grained material slowly propagates due to the tortuous path, and low H;and Cl;concentrations.
文摘The effect of transition elements on grain refinement of 7475 aluminum alloy sheets produced by warm rolling was investigated. The alloy which contains zirconium instead of chromium showed ultra fine structures with stable subgrains after warm rolling at 350 ℃, followed by solution heat treatment at 480 ℃. The average subgrain diameter was approximately 3 pan. It became clear that zirconium in solution has the effect of stabilizing subgrains due to precipitation of fine Al3Zr compounds during warm rolling. On the other hand, chromium-bearing compounds precipitate before warm rolling and they grow up to relatively large size during warm rolling. The warm rolled sheets with fine subgrains have unique properties compared with conventional 7475 aluminum alloy sheets produced by cold rolling. The warm roiled sheets solution heat treated had subgrain structures through the thickness with a high proportion of low-angle boundary less than 15°. The strength of the warm rolled sheets in T6 condition was about 10% higher than that of conventional 7475 aluminum alloy sheets. As the most remarkable point in the warm rolled sheets, the high Lankford （r） value of 3.5 was measured in the orientation of 45° to rolling direction, with the average r-value of 2.2. The high r-value would be derived from well developed r-fiber textures, especially with the strong {011 }（211） brass component. The warm rolled sheets also had high resistance to SCC. From Kikuchi lines analysis and TEM images, it was found that PFZs were hardly formed along the low- angle boundaries of the warm rolled sheets in T6 condition. This would be a factor to lead to the improvement of resistance to SCC because of reducing the difference in electrochemical property between the grain boundary area and the grain interior.
文摘Metallurgical and mechanical properties along with shape memory and corrosion behavior of Cu-11.8% AI-3.7% Ni-1 %Mn and Cu-11% A1 5.6% Mn shape memory alloys （SMAs） were comparatively studied. The influence of grain refinement on the properties was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, differential scanning calorimetry （DSC）, potentiodynamic polarizations and bend and tensile tests. Static recrystallization and kinetic grain growth show a rapid recrystallization in the first 15 s of annealing at 800℃ followed by grain growths. The minimum grain sizes obtained after 15 s are 90 and 260 μm for Cu-A1-Ni-Mn and Cu-A1-Mn, respectively. Tensile tests show typical three-stage curves for both alloys, and it is seen that alloys exhibit high fracture stress and strain after grain refinement. Microstructural observations show zig-zag morphology of β 1martensite in the Cu-A1-Ni-Mn and coexistence of β1 and y1 in the Cu-A1-Mn, which were confirmed by differential scanning calorimetry results. The shape memory ratios （17） of the alloys before thermomechanieal treatment, and after thermomechanical annealing at 800 ℃ for different time up to 15 min followed by water quenching, were evaluated. In addition, corrosion behavior of alloys after grain refinement was analyzed by means of potentiodynamic polarization measurements. The results showed that the anodic reactions were dominated by dissolution of copper, and Cu-AI-Ni-Mn alloy exhibits a better corrosion resistance than Cu-A1-Mn alloy.
文摘Friction stir extrusion(FSE)is known as an innovative manufacturing technology that makes it possible to directly produce wire via consolidation and extrusion of metal chips or solid billets.In this study,wire samples were produced using aluminum alloy AA7022 machining chips by the use of the FSE.To this end,the microstructures and mechanical properties of the base material(BM)and the extruded samples were investigated.The corrosion resistance of the given samples was also determined using potentiodynamic polarization technique.The results showed that the samples manufactured at higher rotational speeds possessed good surface quality,the process temperature and the grain size similarly increased following the rise in rotational speed,and the mechanical properties consequently decreased.Using the FSE led to crystallite refinement,increase in volume fraction of grain boundaries,as well as re-distribution of precipitates affecting corrosion resistance.Furthermore,the findings of the corrosion tests revealed that the produced samples by the FSE had adequate corrosion resistance and the growth in die rotation rate augmented current density and subsequently reduced corrosion resistance.
基金National Natural Science Foundation of China(52071126)Natural Science Foundation of Tianjin City,China(22JCQNJC01240)+2 种基金Central Guidance on Local Science and Technology Development Fund of Hebei Province(226Z1009G)Special Funds for Science and Technology Innovation in Hebei(2022X19)Foundation Strengthening Program(2019-JCJQ-00)。
文摘The corrosion properties of pure zirconium(Zr)with different grain sizes in acid,alkali,and salt environments were studied.The microstructures of pure Zr were observed by optical microscope,X-ray diffractometer,and electron backscattered diffraction probe.The corrosion resistance of pure Zr was analyzed by electrochemical corrosion test and immersion test.Results show that pure Zr with grain size of 4–32μm can be obtained after annealing at 800°C for different durations,and the relationship between grain size and annealing duration is D^(3)−D_(0)^(3)=3.35t.The electrochemical corrosion and immersion corrosion test results show that the pure Zr with grain size of about 24μm(annealing at 800°C for 20 h)possesses the optimal corrosion resistance.
