The surface morphology and chemical composition of the oxide films formed on pure magnesium and AZ91D alloy in aqueous electrolytes which contained sodium hexafluorinealuminate（Na3AlF6）, potassium hydroxide （KOH）,...The surface morphology and chemical composition of the oxide films formed on pure magnesium and AZ91D alloy in aqueous electrolytes which contained sodium hexafluorinealuminate（Na3AlF6）, potassium hydroxide （KOH）, sodium hexametahposphate（（NaPO3）6）, and triethanolamine were investigated by X-ray diffraction（XRD）, scanning electron microscope（SEM） and energy dispersive spectroscopy（EDX）. The results show that the input of the negative pulse has great influences on the quantity and the appearance of the microdischarges. Three types of pores can be distinguished on the surface of the oxide film and their size ranges are 0.5-1μm, 1-2μm and 4-7μm, respectively. A few microcracks are seen around the large pores. There exists a remarkable fluoride- enriched zone of about 4-6μm for pure magnesium and 3-5μm for AZ91D alloy at the coating/substrate interface.展开更多
Anew anodizing process, which does not contain chromate but can improve the corrosion resistance of magnesium alloys significantly, was developed using a microarc power supply. Surface morphology was observed and the ...Anew anodizing process, which does not contain chromate but can improve the corrosion resistance of magnesium alloys significantly, was developed using a microarc power supply. Surface morphology was observed and the coating was compact and ceramic-like. In addition, the corrosion resistance of samples before and after anodization by the new process and a method in US Patent 5470664 was compared by potentiodymaic polarization curves, electrochemical impedance spectroscopy (EIS) and salt spray test. The results show that the anodization can improve the corrosion resistance of magnesium alloy. The samples obtained by the new process and the method mentioned in the US Patent 5470664 achieve 9 and 7 rates after 336 h salt spray test, respectively.展开更多
Magnesium alloy AZ91D was processed respectively in one, two, three and four-component electrolytes by using AC microarc oxidation technique. The corrosion resistance of AZ91D alloy was measured by electrochemical met...Magnesium alloy AZ91D was processed respectively in one, two, three and four-component electrolytes by using AC microarc oxidation technique. The corrosion resistance of AZ91D alloy was measured by electrochemical methods. The optimum electrolytes in two, three and four components were found. In four-component electrolyte composed by NaOH, NaAlOj, H2O2 and C4H4O6N32, the film formed on AZ91D alloy is smooth and compact, and has a higher corrosion resistance. The effect of the ingredients in electrolytes was discussed based on their roles in the formation of corrosion resistant film.展开更多
The compound bioceramic coating containing calcium (Ca) and phosphorus (P) on titanium alloy substrate was prepared by means of micro-arc oxidation (MAO) treatment. The results show that under the different electrolyt...The compound bioceramic coating containing calcium (Ca) and phosphorus (P) on titanium alloy substrate was prepared by means of micro-arc oxidation (MAO) treatment. The results show that under the different electrolyte the coating with the color of gray or black and surface morphology of cauliflower or honeycomb, where Ca content and P contain can attain 30% and 20% respectively, can be obtained. Meanwhile, the influences of electrolyte temperature, current density and discharge time on morphology and thickness of coating are also discussed here.展开更多
Thick and hard ceramic coatings were prepared on the Al-Cu-Mg alloy by microarc oxidation in alkali-silicate electrolytic solution. The thickness and microhardness of the oxide coatings were measured. The influence of...Thick and hard ceramic coatings were prepared on the Al-Cu-Mg alloy by microarc oxidation in alkali-silicate electrolytic solution. The thickness and microhardness of the oxide coatings were measured. The influence of current density on the growth rate of the coating was examined. The microstructure and phase composition of the coatings were investigated by means of scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Moreover, the tensile strength of the Al alloy before and after microarc oxidation treatment were tested, and the fractography and morphology of the oxide coatings were observed using scanning electron microscope. It is found that the current density considerably influences the growth rate of the microarc oxidation coatings. The oxide coating is mainly composed of α-Al2O3 and γ-Al2O3, while high content of Si is observed in the superficial layer of the coating. The cross-section microhardness of 120 μm thick coating reaches the maximum at distance of 35 μm from the substrate/coating interface. The tensile strength and elongation of the coated Al alloy significantly decrease with increasing coating thickness. The microarc oxidation coatings greatly improve the wear resistance of Al alloy, but have high friction coefficient which changes in the range of 0.70.8. Under grease lubricating, friction coefficient is only 0.15 and wear loss is less than 1/10 of the loss under dry friction.展开更多
Metallurgically bonded ceramic coatings were prepared on a steel surface with a combined method of arc spraying and micro-arc oxidation for the first time. Coatings were investigated by X-ray diffraction (XRD) and sca...Metallurgically bonded ceramic coatings were prepared on a steel surface with a combined method of arc spraying and micro-arc oxidation for the first time. Coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Point and line distribution of elements of the ceramic coatings were determined using energy dispersive spectroscopy (EDS). Coatings abrasive wear resistance, corrosion resistance and hot impact property were assessed respectively. The property test results show that metallurgically bonded ceramic coatings were formed on aluminum coatings and the ceramic coatings is mainly composed of a-Al2O3, y-A!2O3^ #-Al2O3 and a little amorphous. The coatings possess excellent abrasive wear, corrosion and hot shock resistance, which can in part be attributed to the gradual distribution of different phases from surface to the substrate.展开更多
In a basic solution containing 18 g/L Na2SiO3,the anodizing of AZ91HP magnesium alloy was investigated with and without addition of phytic acid(C6H18O24P6). The thickness,composition and morphologies of anodic coating...In a basic solution containing 18 g/L Na2SiO3,the anodizing of AZ91HP magnesium alloy was investigated with and without addition of phytic acid(C6H18O24P6). The thickness,composition and morphologies of anodic coatings formed at different concentrations of C6H18O24P6 were determined. The corrosion resistance of anodized samples was evaluated by salt spray test in 5%(mass fraction) NaCl solution. The results show that C6H18O24P6,which is harmless and environmentally friendly,greatly affects the properties of anodic coatings. Under the same electric parameters,the final voltage increases with the concentrations of C6H18O24P6. The coating thickness slightly increases from 8 μm formed in the base electrolyte without C6H18O24P6 to 9-10 μm in C6H18O24P6 solution. The P content and color of anodic coatings separately increases and darkens with the addition of C6H18O24P6. After the anodizing solutions were changed from 0 to 16 g/L addition of C6H18O24P6,the largest size of micropores decreases from 4 μm to 3 μm,while the number of micropores per area on coating surface decreases from 0.076 to 0.047 μm-2. The salt spray test shows that C6H18O24P6 can improve the corrosion resistance of the anodic coatings and the coating formed in the electrolyte containing 12 g/L C6H18O24P6 exhibits the highest corrosion resistance.展开更多
文摘The surface morphology and chemical composition of the oxide films formed on pure magnesium and AZ91D alloy in aqueous electrolytes which contained sodium hexafluorinealuminate（Na3AlF6）, potassium hydroxide （KOH）, sodium hexametahposphate（（NaPO3）6）, and triethanolamine were investigated by X-ray diffraction（XRD）, scanning electron microscope（SEM） and energy dispersive spectroscopy（EDX）. The results show that the input of the negative pulse has great influences on the quantity and the appearance of the microdischarges. Three types of pores can be distinguished on the surface of the oxide film and their size ranges are 0.5-1μm, 1-2μm and 4-7μm, respectively. A few microcracks are seen around the large pores. There exists a remarkable fluoride- enriched zone of about 4-6μm for pure magnesium and 3-5μm for AZ91D alloy at the coating/substrate interface.
文摘Anew anodizing process, which does not contain chromate but can improve the corrosion resistance of magnesium alloys significantly, was developed using a microarc power supply. Surface morphology was observed and the coating was compact and ceramic-like. In addition, the corrosion resistance of samples before and after anodization by the new process and a method in US Patent 5470664 was compared by potentiodymaic polarization curves, electrochemical impedance spectroscopy (EIS) and salt spray test. The results show that the anodization can improve the corrosion resistance of magnesium alloy. The samples obtained by the new process and the method mentioned in the US Patent 5470664 achieve 9 and 7 rates after 336 h salt spray test, respectively.
文摘Magnesium alloy AZ91D was processed respectively in one, two, three and four-component electrolytes by using AC microarc oxidation technique. The corrosion resistance of AZ91D alloy was measured by electrochemical methods. The optimum electrolytes in two, three and four components were found. In four-component electrolyte composed by NaOH, NaAlOj, H2O2 and C4H4O6N32, the film formed on AZ91D alloy is smooth and compact, and has a higher corrosion resistance. The effect of the ingredients in electrolytes was discussed based on their roles in the formation of corrosion resistant film.
文摘The compound bioceramic coating containing calcium (Ca) and phosphorus (P) on titanium alloy substrate was prepared by means of micro-arc oxidation (MAO) treatment. The results show that under the different electrolyte the coating with the color of gray or black and surface morphology of cauliflower or honeycomb, where Ca content and P contain can attain 30% and 20% respectively, can be obtained. Meanwhile, the influences of electrolyte temperature, current density and discharge time on morphology and thickness of coating are also discussed here.
文摘Thick and hard ceramic coatings were prepared on the Al-Cu-Mg alloy by microarc oxidation in alkali-silicate electrolytic solution. The thickness and microhardness of the oxide coatings were measured. The influence of current density on the growth rate of the coating was examined. The microstructure and phase composition of the coatings were investigated by means of scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Moreover, the tensile strength of the Al alloy before and after microarc oxidation treatment were tested, and the fractography and morphology of the oxide coatings were observed using scanning electron microscope. It is found that the current density considerably influences the growth rate of the microarc oxidation coatings. The oxide coating is mainly composed of α-Al2O3 and γ-Al2O3, while high content of Si is observed in the superficial layer of the coating. The cross-section microhardness of 120 μm thick coating reaches the maximum at distance of 35 μm from the substrate/coating interface. The tensile strength and elongation of the coated Al alloy significantly decrease with increasing coating thickness. The microarc oxidation coatings greatly improve the wear resistance of Al alloy, but have high friction coefficient which changes in the range of 0.70.8. Under grease lubricating, friction coefficient is only 0.15 and wear loss is less than 1/10 of the loss under dry friction.
文摘Metallurgically bonded ceramic coatings were prepared on a steel surface with a combined method of arc spraying and micro-arc oxidation for the first time. Coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Point and line distribution of elements of the ceramic coatings were determined using energy dispersive spectroscopy (EDS). Coatings abrasive wear resistance, corrosion resistance and hot impact property were assessed respectively. The property test results show that metallurgically bonded ceramic coatings were formed on aluminum coatings and the ceramic coatings is mainly composed of a-Al2O3, y-A!2O3^ #-Al2O3 and a little amorphous. The coatings possess excellent abrasive wear, corrosion and hot shock resistance, which can in part be attributed to the gradual distribution of different phases from surface to the substrate.
基金Project(0650034) supported by the Natural Science Foundation of Jiangxi Province, China
文摘In a basic solution containing 18 g/L Na2SiO3,the anodizing of AZ91HP magnesium alloy was investigated with and without addition of phytic acid(C6H18O24P6). The thickness,composition and morphologies of anodic coatings formed at different concentrations of C6H18O24P6 were determined. The corrosion resistance of anodized samples was evaluated by salt spray test in 5%(mass fraction) NaCl solution. The results show that C6H18O24P6,which is harmless and environmentally friendly,greatly affects the properties of anodic coatings. Under the same electric parameters,the final voltage increases with the concentrations of C6H18O24P6. The coating thickness slightly increases from 8 μm formed in the base electrolyte without C6H18O24P6 to 9-10 μm in C6H18O24P6 solution. The P content and color of anodic coatings separately increases and darkens with the addition of C6H18O24P6. After the anodizing solutions were changed from 0 to 16 g/L addition of C6H18O24P6,the largest size of micropores decreases from 4 μm to 3 μm,while the number of micropores per area on coating surface decreases from 0.076 to 0.047 μm-2. The salt spray test shows that C6H18O24P6 can improve the corrosion resistance of the anodic coatings and the coating formed in the electrolyte containing 12 g/L C6H18O24P6 exhibits the highest corrosion resistance.
