The grain refinement of the as-cast AZ31 alloys by limestone particles was investigated by grain refining tests and microstructure observations. The results show that the limestone particles have a good grain refining...The grain refinement of the as-cast AZ31 alloys by limestone particles was investigated by grain refining tests and microstructure observations. The results show that the limestone particles have a good grain refining potency, which is deeply related to the addition level of limestone and melting temperature. The optimal addition level and melting temperature are 2.0%（mass fraction） and 720 ℃, respectively. The average grain size of AZ31 alloy is reduced from（556±60） to（236±22） μm. The sound grain refining by raw limestone particles has a good anti-fading capacity without any significant grain coarsening in a 40 min holding time. The concerned grain refining mechanism should be attributed to the inoculated Al-C and Al-C/Al-Mn-（Fe） nuclei. Ultrasonic treatment can enhance the grain refining efficiency of limestone particles through cavitation-enhanced nucleation mechanism.展开更多
A fluidized-bed magnetizing roasting-magnetic separation process was selected to treat this type of material.Phase transformations and microstructural changes in the product resulting from magnetizing roasting under d...A fluidized-bed magnetizing roasting-magnetic separation process was selected to treat this type of material.Phase transformations and microstructural changes in the product resulting from magnetizing roasting under different reducing gases(CO,H2,CO+H2)were clarified by vibrating sample magnetometry,X-ray diffraction,scanning electron microscopy,and energy-dispersive X-ray spectroscopy.The results indicated that the conversion ratio and saturation magnetization of samples roasted in a mixed gas of CO and H2 were higher than those of samples produced under CO or H2 alone.This indicated that synergy of the combined CO and H2 gas had a positive effect on the fluidized-bed magnetizing roasting process.The mechanism and kinetics of the improved magnetizing roasting of a siderite-hematite iron ore mixture under this synergistic CO-H2 system were investigated under isothermal conditions.The results indicated that the apparent activation energies of the reactions of the iron oxides decreased from 37.7 and 17.9 to 15.9 kJ/moI when the roasting atmosphere was changed from pure H2 or CO to a gas mixture of CO and H2,respectively.The mixed CO-H2 gas promoted the conversion ratio of hematite and siderite to magnetite,thereby improving the conversion ratio in the fluidized-bed magnetizing roasting process.展开更多
基金Project(2016YFB0301104)supported by National Key Research and Development Program of China
文摘The grain refinement of the as-cast AZ31 alloys by limestone particles was investigated by grain refining tests and microstructure observations. The results show that the limestone particles have a good grain refining potency, which is deeply related to the addition level of limestone and melting temperature. The optimal addition level and melting temperature are 2.0%（mass fraction） and 720 ℃, respectively. The average grain size of AZ31 alloy is reduced from（556±60） to（236±22） μm. The sound grain refining by raw limestone particles has a good anti-fading capacity without any significant grain coarsening in a 40 min holding time. The concerned grain refining mechanism should be attributed to the inoculated Al-C and Al-C/Al-Mn-（Fe） nuclei. Ultrasonic treatment can enhance the grain refining efficiency of limestone particles through cavitation-enhanced nucleation mechanism.
基金The authors would like to express their thanks to the National Natural Science Foundation of China(No.5157041410)for the financial support of this research.
文摘A fluidized-bed magnetizing roasting-magnetic separation process was selected to treat this type of material.Phase transformations and microstructural changes in the product resulting from magnetizing roasting under different reducing gases(CO,H2,CO+H2)were clarified by vibrating sample magnetometry,X-ray diffraction,scanning electron microscopy,and energy-dispersive X-ray spectroscopy.The results indicated that the conversion ratio and saturation magnetization of samples roasted in a mixed gas of CO and H2 were higher than those of samples produced under CO or H2 alone.This indicated that synergy of the combined CO and H2 gas had a positive effect on the fluidized-bed magnetizing roasting process.The mechanism and kinetics of the improved magnetizing roasting of a siderite-hematite iron ore mixture under this synergistic CO-H2 system were investigated under isothermal conditions.The results indicated that the apparent activation energies of the reactions of the iron oxides decreased from 37.7 and 17.9 to 15.9 kJ/moI when the roasting atmosphere was changed from pure H2 or CO to a gas mixture of CO and H2,respectively.The mixed CO-H2 gas promoted the conversion ratio of hematite and siderite to magnetite,thereby improving the conversion ratio in the fluidized-bed magnetizing roasting process.
