Effects of Modifier-treatment on the Corrosion Resisitance Properties of As-cast Al-5wt.%Cu Alloy in NaCl Solution

Effects of Modifier-treatment on the Corrosion Resisitance Properties of As-cast Al-5wt.%Cu Alloy in NaCl Solution
　　Aluminum alloys as traditional metal materials with lower density, higher specific strength, heat machining capability,are widely used in aerospace, automobile. With the rapid development of modern industry, the need of structures existed stengthen and toughening and light-weight together is urgent. Applications of Aluminum alloys will become more and more wide. As a result, people demand for as-cast Al alloy with more higher mechanical properties. So the high strength and toughness aluminum alloys has its development chance to research and applications. in system of aluminum alloys, Al-Cu alloy turn into hot focus of high tensile strength and ductility aluminum alloys,because of its well mechanical properties. However, Al-Cu alloy as a high tensile strength and ductility aluminum alloy, has poor corrosion resistance.its applications have potential hazard to bring tremendous economy loss and catastrophic accident. So the applications are limited for Block Neodymium magnets intergranular corrosion mainly. when strength and ductility of Al-Cu alloy is researched, its corrosion resistance is investigated at the same time,which have important signification of theory and practice. Al-Cu alloy is researched as a target for its properties, the present study has utilized different modifiers treatment technology to improve the corrosion resistance of the Al-Cu alloy.
　　The efforts on the corrosion resistance of the present alloy with different modifiers technology are also investigated, at the same time, the optimal modifier and its content in the alloy are optimized. The study discussed the corrosion resistance mechanism of the alloy preliminary, which can be achieved depended on analyzing the average weight loss, average loss rate,the corrosive morphology and electrochemistry behavior of the alloys. All above has important signification of theory and practice to make high tensile strength and ductility aluminum alloys with excellent corrosion Block Neodymium magnets resistance.The results showed: the three modifiers used in the experiment improved the corrosion resistance of the alloy in various degrees. It can be judged that: first,the corrosion resistance of the alloy with 0.1wt.% Sc is best, when the alloy is modified by Sc only; secondly, the corrosion resistance of the alloy with 0.4 wt.% Ag is best, when the alloy is modified by Ag only; thirdly, the corrosion resistance http://www.999magnet.com/ of the alloy with 1.5 wt.% PrxOy is best, when the alloy is modified by PrxOy only.
　　By contrasting the corrosion resistance of the above alloys, it can be found that the corrosion resistance of the alloy is improving remarkably when it is modified by 1.5wt.% PrxOy. The average weight loss of the alloy modified by 1.5 wt.% PrxOy decreased 47.53%, and its average loss rate reduced 24% compared with the unmodified alloy. The corrosion resistance property of the alloy is so well enough that there is not report concerning the similar alloy in home and abroad provisionally. Its application in the fields of automotive and aerospace will be wide and nice in the future. Through the measurement of the polarization curves and the corrosion potential, breakdown potential, we can know that the alloys modified showed a stable passivation area after activation-passivation transition area, but it can not be found in the unmodified alloy.The corrosion potentials and the breakdown potentials of the alloys present a trend of increase and then decrease when we add more PrxOy in the alloys. Especially, the corrosion potential of the alloy modified by 1.5wt.% PrxOy whose breakdown potential is -10.658V, is -1.069V. The increasing of the corrosion value indicated the trend of the alloy corrosion is lower, accordingly the higher breakdown potential showed the occurrence of the pitting corrosion is more difficult on the modified alloys’surface. So the corrosion resistance of the alloy is improved. We analysed the electrochemical impedance spectroscopy of the alloys in 3.5wt.% solution and learned that the oxide film on the alloy surface modified by 1.5wt.% PrxOy was relatively integrated, which protected the alloy well; moreover, the high resistance reaction inhibited the formation of the pitting and improved the corrosion resistance of the alloy.Al-Cu alloys had poor corrosion resistance.
　　The intergranular corrosion of the Al-Cu alloys was caused by second-phase precipitation in grain boundaries and precipitate free zone in near area. As different corrosion potentials among precipitate phase, precipitate free zone and grain self; when corrosion medium existed, numberless electrochemistry tiny-batteries came into being, which resulted in channels of anode dissolve over grain boundaries, this was intergranular corrosion. The corrosion resistance of the present Al-Cu alloy improved for the addition of rare-earth oxide obviously. The reasons are: for one thing, the alloy modified by rare-earth oxide, caused the structure more uniform, made the grains smaller, restrained the second-phase particles growing up and gathering, reduced the cracks of the structure, so decreased the corrosion sensitivity greatly. The surface of the alloy produced uniform and stable oxide film fast after the film formed in the air naturally had been destroyed, which can prevent the surface corroding, http://www.999magnet.com/ control the corrosion hole growing up. For another thing, it reduced the grain boundary attenuation, restrained the growing of the PFZ and the second-phases near the boundaty, so the degree of the corrosion would be reduce. There is not obvious anodic corrosion channel, which restrained the corrosion, simultaneously caused the film to be difficult to break and easy to obtain repair. It became difficult that the further expansion and connected to corrosion area of the corrosion holes. All above reduced the grain flaking possibility fundamentally.