Influences of rare earth （RE） elements addition on thermal fatigue behaviors of AZ91 alloy were studied. Repeated heating and cooling cycles were applied on the samples at 170 and 210℃ to develop thermal fatigue cr...Influences of rare earth （RE） elements addition on thermal fatigue behaviors of AZ91 alloy were studied. Repeated heating and cooling cycles were applied on the samples at 170 and 210℃ to develop thermal fatigue cracks. Crack growth mechanisms and microstructural influences were investigated by optical and scanning electron microscopy （SEM） as well as energy dispersive X-ray spectroscopy （EDS）. Thermal fatigue behaviors were observed to improve successively by addition of the RE up to 2wt.%. This improvement was attributed to the consummation of aluminum in melt by precipitation of the needle shaped AII1RE3 phases. This process was attributed to the reduction of MglTAl12 phase volume fraction and consequent decrease of the brittle Mg/MglTAl12 interface which was the main reason for weak thermal properties of the alloy at rather high temperatures. Further additions of RE, however, reduced the thermal shock resistance of the samples by increasing the mean length of the brittle needle shaped phases.展开更多
In order to develop the ignition-proof magnesium alloy,the effect of alloying elements,Ca and Y,on the oxidation behavior of AZ91 magnesium alloy at elevated temperatures was investigated. The ignition-proof performan...In order to develop the ignition-proof magnesium alloy,the effect of alloying elements,Ca and Y,on the oxidation behavior of AZ91 magnesium alloy at elevated temperatures was investigated. The ignition-proof performance,oxide products and oxidation kinetics of Ca-and Y-containing AZ91 alloys were studied. The results indicate that the proper addition of Ca can increase the ignition point of AZ91 alloy greatly. However,the oxide film of Ca-bearing AZ91 alloy formed at elevated temperature is thick and brittle,which is prone to crack in melting and cooling process. In addition,the oxide film of AZ91-xCa alloy is incompact and cannot inhibit the diffusion of reaction particles. The oxide film of AZ91-xCa alloy turns to thin and plastic one after Y is added,and the density of the oxide film increases greatly due to the formation of composite oxide film composed of MgO,CaO and Y2O3.展开更多
The influence of heat treatment（T6） on the ambient temperature dry sliding wear behavior of the extruded AZ91 alloy treated with Y using a pin-on-disc apparatus was investigated. Wear rates and friction coefficients...The influence of heat treatment（T6） on the ambient temperature dry sliding wear behavior of the extruded AZ91 alloy treated with Y using a pin-on-disc apparatus was investigated. Wear rates and friction coefficients were measured within a load range of 5-70 N at a sliding speed of 0.188 m/s over a constant sliding distance of 226.195 m. Worn surfaces and debris were examined using a scanning electron microscope equipped with an energy dispersive spectrometer. The experimental results revealed that, as applied load was increased, the alloy wear rates increased, but the friction coefficients decreased. Four chief operating wear mechanisms were observed, i.e., abrasion, oxidation, delamination and plastic deformation. The extruded AZ91 alloy treated with Y exhibited better wear resistance by adopting T6, which was mainly due to large amounts of fine Mg_（17）Al_（12） distributed in the grains and the resulting modified strength and micro-hardness.展开更多
文摘Influences of rare earth （RE） elements addition on thermal fatigue behaviors of AZ91 alloy were studied. Repeated heating and cooling cycles were applied on the samples at 170 and 210℃ to develop thermal fatigue cracks. Crack growth mechanisms and microstructural influences were investigated by optical and scanning electron microscopy （SEM） as well as energy dispersive X-ray spectroscopy （EDS）. Thermal fatigue behaviors were observed to improve successively by addition of the RE up to 2wt.%. This improvement was attributed to the consummation of aluminum in melt by precipitation of the needle shaped AII1RE3 phases. This process was attributed to the reduction of MglTAl12 phase volume fraction and consequent decrease of the brittle Mg/MglTAl12 interface which was the main reason for weak thermal properties of the alloy at rather high temperatures. Further additions of RE, however, reduced the thermal shock resistance of the samples by increasing the mean length of the brittle needle shaped phases.
基金Project(50271055) supported by the National Natural Science Foundation of ChinaProject(01G53048) supported by the Aviation Foundation of ChinaProject(2002699018) supported by the Doctorate Foundation of the Education Ministry of China
文摘In order to develop the ignition-proof magnesium alloy,the effect of alloying elements,Ca and Y,on the oxidation behavior of AZ91 magnesium alloy at elevated temperatures was investigated. The ignition-proof performance,oxide products and oxidation kinetics of Ca-and Y-containing AZ91 alloys were studied. The results indicate that the proper addition of Ca can increase the ignition point of AZ91 alloy greatly. However,the oxide film of Ca-bearing AZ91 alloy formed at elevated temperature is thick and brittle,which is prone to crack in melting and cooling process. In addition,the oxide film of AZ91-xCa alloy is incompact and cannot inhibit the diffusion of reaction particles. The oxide film of AZ91-xCa alloy turns to thin and plastic one after Y is added,and the density of the oxide film increases greatly due to the formation of composite oxide film composed of MgO,CaO and Y2O3.
基金supported by the National Natural Science Foundation of China(51364035)
文摘The influence of heat treatment（T6） on the ambient temperature dry sliding wear behavior of the extruded AZ91 alloy treated with Y using a pin-on-disc apparatus was investigated. Wear rates and friction coefficients were measured within a load range of 5-70 N at a sliding speed of 0.188 m/s over a constant sliding distance of 226.195 m. Worn surfaces and debris were examined using a scanning electron microscope equipped with an energy dispersive spectrometer. The experimental results revealed that, as applied load was increased, the alloy wear rates increased, but the friction coefficients decreased. Four chief operating wear mechanisms were observed, i.e., abrasion, oxidation, delamination and plastic deformation. The extruded AZ91 alloy treated with Y exhibited better wear resistance by adopting T6, which was mainly due to large amounts of fine Mg_（17）Al_（12） distributed in the grains and the resulting modified strength and micro-hardness.
