Research Co Trace Elements Affect The Corrosion Resistance Of The Alloy Cu28Zn15Ni13Mn

Research the influence of trace element Co on the corrosion resistance of Cu28Zn15Ni13Mn alloy as-cast and deformation-aging in3.5%NaCl solution and simulated sweat solution by the immersion test (static corrosion rate measurement, corrosion morphology observation) and electrochemical test (open circuit potential, polarization curves, electrochemical impedance spectroscopy), combines with the metallographic analysis, scanning electron microscopy and energy spectrum analysis and X ray diffraction analysis to investigate the effect of Co on the corrosion resistance of alloy as-cast and deformation-aging. The research results show that:(1) The test of the static corrosion rate measurement shows that the corrosion rate of alloy with different content of Co, which marinated in3.5%NaCl solution and simulated sweat solution, decreases with the increase of time.45days later, the corrosion resistant level is sixth grade for each alloy in3.5%NaCl solution, the corrosion resistance is ok. The corrosion resistant level is fiveth grade for each alloy in simulated sweat solution, the corrosion resistance of alloy is good. The corrosion resistance of alloy can be improved by adding Co. The alloy as-cast with0.51%Co has the best corrosion resistance; the deformation-aging alloy with0.18%Co addition has the best corrosion resistance. The corrosion rate of the deformation-aging alloy is lower than the alloy as-cast with a certain Co.(2) The test of the surface corrosion morphology observation in3.5%NaCl solution shows that:since the microstructure of the alloy as-cast is coarse dendritic shape with much grain boundary edges, so that the grain boundary has the poor corrosion resistance, the corrosion starts from the grain boundaries. With the extension of immersion time, the corrosion expands from the grain boundary to the crystal. After the addition of Co the alloy dendrite is interrupted, the grain becomes rounded, the grain boundry becomes smoothed, and the electrode potential of Co is higher than Zn, Mn, the addition of Co can improve the overall potential of the alloy, thereby improving the corrosion resistance of the alloy. Because of the appearance of the second phase precipitates in the process of deformation and aging treatment, and the existence of the potential difference between the second phase and matrix, therefore, the corrosion is more serious around the second phase. After the addition of Co, the potential difference between the second phases and the matrix is reduced, the corrosion resistance of the deformation-aging alloy is improved, and the corrosion rate of the alloy with0.18%Co addition is decreased about7%than the alloy without Co addition. However, when the content of Co is excessive, the potential difference between the matrix and second will increase, in addition, the more content of Co the more precipitation of second phase and the more corrosion cell quantity, therefore the corrosion resistance of the alloy decreases. (3) The test of the surface corrosion morphology observation in simulated sweat solution shows that the corrosion of the as-cast alloy which with the dendrite morphology starts from the grain boundaries, and as the corrosion time prolongs, the corrosion of the alloy is more serious. The corrosion color of the alloy with Co addition is light after corrosion, the corrosion color of the alloy without Co addition is deep after corrosion. The deformation-aging alloy exhibit a fibrous tissue, explains that the corrosion is beginning from the grain boundary, meanwhile the corrosion color is deeper in the surrounding of second phase. The corrosion color of the deformation-aging alloy without Co addition is deep, however the corrosion color of the deformation-aging alloy with Co addition is light.(4) The electrochemical test results in3.5%NaCl solution and simulated sweat are consitent with the results of the immersion test, which further proofs the influence and law of Co content on the corrosion resistance of the alloy. The alloy as-cast with0.51%Co addition has the best corrosion resistance; the deformation-aging alloy with0.18%Co addition has the best corrosion resistance. When the content of Co is certain, because of the deformation and heat treatment can improve or even eliminate the defects of alloy as-cast, such as loosen and pores, therefore the corrosion resistance of the deformation-aging alloy is better than the alloy as-cast.