The magnesium alloy is prone to burn during die-casting, which limits its applications severely, so the effect of adding rare earth （RE） on the ignition-proof of AZ91D Mg alloy is studied. The results indicate that ...The magnesium alloy is prone to burn during die-casting, which limits its applications severely, so the effect of adding rare earth （RE） on the ignition-proof of AZ91D Mg alloy is studied. The results indicate that the addition of mischmetal RE elements has a remarkable influence on the ignition-proof property of the magnesium alloy. It is found that the ignition temperature of the magnesium alloy can be greatly raised by adding a proper amount of RE. When the amount is 0.1wt%, the ignition temperature reaches 877℃ which is 206℃ higher than that of AZ91D without RE and the mechanical properties of the alloy are also improved, However, the amount of RE must be properly controlled because too much RE would induce grain coarsening and reduce the mechanical properties.展开更多
The effect of Ce on ignition point of AZ91D magnesium alloy chips was studied. For the AZ91D and the AZ91D-xCe magnesium alloys, changing the sizes of the chips in the range of 58 - 270 μm has a limited influence on ...The effect of Ce on ignition point of AZ91D magnesium alloy chips was studied. For the AZ91D and the AZ91D-xCe magnesium alloys, changing the sizes of the chips in the range of 58 - 270 μm has a limited influence on ignition point, however, the shift of the content of Ce has much effect on ignition point. Increasing the Ce content, x from 0.15 to 0.25, the ignition point increases with increasing of Ce; however, x from 0.25 to 0.45, the ignition point decreases with increasing of Ce. By the addition of Ce of 0.25 %. the ignition point is raised by 43℃.展开更多
Fatigue strength,crack initiation and propagation behavior of rolled AZ31B magnesium alloy plate were investigated. Axial tension-compression fatigue tests were carried out with cylindrical smooth specimens.Two types ...Fatigue strength,crack initiation and propagation behavior of rolled AZ31B magnesium alloy plate were investigated. Axial tension-compression fatigue tests were carried out with cylindrical smooth specimens.Two types of specimens were machined with the loading axis parallel(L-specimen)and perpendicular(T-specimen)to rolling direction.Monotonic compressive 0.2%proof stress,tensile strength and tensile elongation were similar for both specimens.On the other hand,monotonic tensile 0.2%proof stress of the L-specimen was slightly higher than that of the T-specimen.Moreover,monotonic compressive 0.2%proof stresses were lower than tensile ones for both specimens.The fatigue strengths of 107cycles of the L-and T-specimens were 95 and 85 MPa,respectively. Compared with the monotonic compressive 0.2%proof stresses,the fatigue strengths were higher for both specimens.In other words, the fatigue crack did not initiate and propagate even though deformation twins were formed in compressive stress under the cyclic tension-compression loading.The fatigue crack initiated at early stage of the fatigue life in low cycle regime regardless of specimen direction.The crack growth rate of the L-specimen was slightly lower than of the T-specimen.Consequently,the fatigue lives of the L-specimen were longer than those of the T-specimen in low cycle regime.展开更多
Good ignition-proof principle and mechanical properties were realized in Mg-Y-Ca-Zr alloy system.By adding Y and Ca elements,the ignition point of Mg-3.5Y-0.8Ca alloy was improved to over 1173 K,and the alloy could be...Good ignition-proof principle and mechanical properties were realized in Mg-Y-Ca-Zr alloy system.By adding Y and Ca elements,the ignition point of Mg-3.5Y-0.8Ca alloy was improved to over 1173 K,and the alloy could be melted in air without any protections.The ef-fect of Zr addition on the microstructures and mechanical properties of Mg-3.5Y-0.8Ca alloys were investigated,and Mg-3.5%Y-0.8%Ca-0.4%Zr alloy had good comprehensive properties with tensile strength of 190 MPa and elongation of 11%.Auger electron spectros-copy（AES） and X-ray diffraction（XRD） analysis revealed that the oxide film formed on the surface of Mg-3.5Y-0.8Ca alloy was mainly composed of Y2O3.Thermogravimetric measurements in dry air indicated that the oxidation dynamics curves measured at 773,873 and 973 K followed the cubic law.Moreover,the semiconductor characteristic of Y2O3 film and its effect on ignition-proof properties of Magnesium al-loys were discussed from the viewpoint of electrochemistry.展开更多
The surface segregation of La and its effect on the oxygen adsorption on a Mg （0001） surface for a coverage 0=-0.25 monolayer were performed by using first-principles calculations. The calculated results showed that...The surface segregation of La and its effect on the oxygen adsorption on a Mg （0001） surface for a coverage 0=-0.25 monolayer were performed by using first-principles calculations. The calculated results showed that La atoms preferred occupying surface sites to the bulk sites, which suggested the La surface segregation. When oxygen atoms adsorbed on a pure or La alloyed Mg （0001） surface, certain amount of heat would release, and La alloying made the heat released less, which might increase the ignition point of Mg alloy. Both Mg and La had strong atomic affinity with oxygen, so the oxidation film of Mg-La alloys consisted of MgO, La2O3. The denser La2O3 turned oxide film into free and close structure, and prevented oxygen from passing through the oxidation film. The La-O covalent bonding could explain why La2O3 was compact, and resulted in good ignition-proof of Mg-La alloys.展开更多
A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning ele...A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and thermodynamics calculation at 673, 773 and 873 K. XRD and SEM analysis indicated that dense and compact oxide films composed of MgO, Y203 and CaO formed. The oxidation behavior was characterized by the selective oxidation. Based on Pilling-Bedworth ra- tio （PBR） and energy dispersive spectrometer （EDS） analysis, Y203 contributed more to form the compact surface oxide film, which led to the excellent ignition-proof performance. The thermodynamics analysis and EDS results implied that the Y-rich areas were preferred paths for the selective oxidation.展开更多
文摘The magnesium alloy is prone to burn during die-casting, which limits its applications severely, so the effect of adding rare earth （RE） on the ignition-proof of AZ91D Mg alloy is studied. The results indicate that the addition of mischmetal RE elements has a remarkable influence on the ignition-proof property of the magnesium alloy. It is found that the ignition temperature of the magnesium alloy can be greatly raised by adding a proper amount of RE. When the amount is 0.1wt%, the ignition temperature reaches 877℃ which is 206℃ higher than that of AZ91D without RE and the mechanical properties of the alloy are also improved, However, the amount of RE must be properly controlled because too much RE would induce grain coarsening and reduce the mechanical properties.
文摘The effect of Ce on ignition point of AZ91D magnesium alloy chips was studied. For the AZ91D and the AZ91D-xCe magnesium alloys, changing the sizes of the chips in the range of 58 - 270 μm has a limited influence on ignition point, however, the shift of the content of Ce has much effect on ignition point. Increasing the Ce content, x from 0.15 to 0.25, the ignition point increases with increasing of Ce; however, x from 0.25 to 0.45, the ignition point decreases with increasing of Ce. By the addition of Ce of 0.25 %. the ignition point is raised by 43℃.
文摘Fatigue strength,crack initiation and propagation behavior of rolled AZ31B magnesium alloy plate were investigated. Axial tension-compression fatigue tests were carried out with cylindrical smooth specimens.Two types of specimens were machined with the loading axis parallel(L-specimen)and perpendicular(T-specimen)to rolling direction.Monotonic compressive 0.2%proof stress,tensile strength and tensile elongation were similar for both specimens.On the other hand,monotonic tensile 0.2%proof stress of the L-specimen was slightly higher than that of the T-specimen.Moreover,monotonic compressive 0.2%proof stresses were lower than tensile ones for both specimens.The fatigue strengths of 107cycles of the L-and T-specimens were 95 and 85 MPa,respectively. Compared with the monotonic compressive 0.2%proof stresses,the fatigue strengths were higher for both specimens.In other words, the fatigue crack did not initiate and propagate even though deformation twins were formed in compressive stress under the cyclic tension-compression loading.The fatigue crack initiated at early stage of the fatigue life in low cycle regime regardless of specimen direction.The crack growth rate of the L-specimen was slightly lower than of the T-specimen.Consequently,the fatigue lives of the L-specimen were longer than those of the T-specimen in low cycle regime.
基金Project supported by the National Natural Science Foundation of China (50901048,51174143)the fund of the State Key Laboratory of Solidification Processing in NWPU (SKLSP201003)+1 种基金Program for Changjiang Scholar and Innovative Research Team in University (IRT0972)Program for the Top Young Academic Leaders of Higher Learning Institutions of Shanxi and Natural Science Foundation of Shanxi (2010021022-5)
文摘Good ignition-proof principle and mechanical properties were realized in Mg-Y-Ca-Zr alloy system.By adding Y and Ca elements,the ignition point of Mg-3.5Y-0.8Ca alloy was improved to over 1173 K,and the alloy could be melted in air without any protections.The ef-fect of Zr addition on the microstructures and mechanical properties of Mg-3.5Y-0.8Ca alloys were investigated,and Mg-3.5%Y-0.8%Ca-0.4%Zr alloy had good comprehensive properties with tensile strength of 190 MPa and elongation of 11%.Auger electron spectros-copy（AES） and X-ray diffraction（XRD） analysis revealed that the oxide film formed on the surface of Mg-3.5Y-0.8Ca alloy was mainly composed of Y2O3.Thermogravimetric measurements in dry air indicated that the oxidation dynamics curves measured at 773,873 and 973 K followed the cubic law.Moreover,the semiconductor characteristic of Y2O3 film and its effect on ignition-proof properties of Magnesium al-loys were discussed from the viewpoint of electrochemistry.
基金National Natural Science Foundation of China(50671069)Natural Science Foundation of Liaoning Province(20102173)the Experimental Central Director’s Foundation of Shenyang Normal University(Sy201103)
文摘The surface segregation of La and its effect on the oxygen adsorption on a Mg （0001） surface for a coverage 0=-0.25 monolayer were performed by using first-principles calculations. The calculated results showed that La atoms preferred occupying surface sites to the bulk sites, which suggested the La surface segregation. When oxygen atoms adsorbed on a pure or La alloyed Mg （0001） surface, certain amount of heat would release, and La alloying made the heat released less, which might increase the ignition point of Mg alloy. Both Mg and La had strong atomic affinity with oxygen, so the oxidation film of Mg-La alloys consisted of MgO, La2O3. The denser La2O3 turned oxide film into free and close structure, and prevented oxygen from passing through the oxidation film. The La-O covalent bonding could explain why La2O3 was compact, and resulted in good ignition-proof of Mg-La alloys.
基金Project supported by the National Key Technology R&D Program(2011BAE22B06)National Natural Science Foundation of China(51101100)
文摘A Mg-Y-Ca-Ce magnesium alloy was optimized for high ignition-proof property, which did not bum in air at 1233 K up to 30 min. Oxidation behavior of the alloy was investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, and thermodynamics calculation at 673, 773 and 873 K. XRD and SEM analysis indicated that dense and compact oxide films composed of MgO, Y203 and CaO formed. The oxidation behavior was characterized by the selective oxidation. Based on Pilling-Bedworth ra- tio （PBR） and energy dispersive spectrometer （EDS） analysis, Y203 contributed more to form the compact surface oxide film, which led to the excellent ignition-proof performance. The thermodynamics analysis and EDS results implied that the Y-rich areas were preferred paths for the selective oxidation.
