·626· 北京科技大学学报 2004年第6期 Degradation of Paint Finishing on Magnesium Alloys in Salt Spray Characterized by Electrochemical Impedance Spectroscopy TU Yunhua,GAO Jin,LI Jiuging,ZHANG Wei Materials Science and Engineering School,University and Science and Technology Beijing;Beijing Key Laboratory for Corrosion,Erosion and Surface Technology,Beijing,100083,China ABSTRACT Compared with painted carbon steel,the degradation of the paint finishing system of magnesium all- oys in salt spray was studied by Electrochemical Impedance Spectroscopy(EIS).The result showed that whether based on chromate conversion coating or not,the electrode process of the paint system on magnesium alloys was more inclined to be controlled by diffusion than that on carbon steel,and the slop of the diffusion line was less than 1.The possible reason was given.It was proved that inductance unit existed in the finishing system with chromate conversion coating.The coating resistance and capacitance were calculated with all EIS data.The finishing system with chromate conversion coating absorbed much more water and corroded more severely than that without chro- mate conversion coating.The calculated values were not fixed but varied,and the more severely the coating degrad- ed,the more widely the value ranged. KEY WORDS magnesium alloys;impedance spectroscopy;salt spray;paint finishing;degradation (上接第607页) Vanadium Effect on Microstructure and Properties of Medium Chromium White Cast Iron LIU Keming,WANG Fuming,HAO Jingwei.YU Huang Metallurgical and Ecological Engineering School,University of Science and Technology Beijing,Beijing 100083,China ABSTRACT In order to study the effect of vanadium addition on the microstructure and properties of medium chromium white cast iron,the microstructure and composition of samples made of the cast iron were analyzed by SEM and EDS.The impact energy and Rockwell hardness of the samples were tested.The results indicate that with an increase in vanadium content,the microstructure of medium chromium white cast iron becomes finer and the im- pact energy values are enhanced.When the mass fraction of vanadium exceeds 4%,a large amount of VC precipi- tates occur,which make the cast iron have potentially favorable wear resistance. KEY WORDS vanadium;medium chromium white cast iron;mechanical properties一 ‘ 北 京 科 技 大 学 学 报 年 第 期 “ ， 口 ， ， 刁刀 眺 呢 ， 毗 几 即 ， ， ， ， 幻 ， 嗯 叮 勿 ， 帅 巧 ， 助 初 ， 叨 ， 上 接 第 页 、 乞 认电 功 洲刀 ， 儿咬口 ， 口 飞 ， 罗 ， ， ， 勿 叭 ， 奴 切 而 飞 ， ， 币