Fe32Mn3Al7Cr反铁磁精密电阻合金激光熔凝层的抗蚀性研究

Corrosion Resistance of Laser Surface Melted Fe32Mn3Al7Cr Antiferromagnetic Precision Resistance Alloy

摘要:

采用HF-4工业用横流CO2激光照射Fe32Mn3Al7Cr反铁磁精密电阻合金，进行激光表面熔凝抗腐蚀改性。研究Fe32Mn3Al7Cr合金激光熔凝层的显微组织、相结构，显微硬度和抗蚀性。合金激光熔凝层具有细密均匀的单相奥氏体组织，依次由细小等轴胞状组织区、柱状组织区与热影响区组成，熔凝层厚度约为650 mm。激光熔凝层的显微硬度HV0.5 N约为16 GPa，较合金基体提高1倍。在1 mol/L Na2SO4溶液中，激光熔凝层距表面深度100和350 μm的阳极极化曲线，均呈现无活化-钝化转变区的自钝化特征，自腐蚀电位Ecorr由原始合金的–658 mV(SCE) 分别增至–420和–478 mV(SCE)，致钝电流密度ipp由2.9 μA/cm2分别降至1.3和1.0 μA/cm2，等轴胞状组织和柱状组织的激光熔凝层具有相近的抗均匀腐蚀性能。在pH=14的0.1 mol/L NaCl 溶液中，激光熔凝层的阳极极化曲线由原始合金的钝化-孔蚀击穿过程转变为钝化-过钝化溶解过程，无孔蚀发生。激光熔凝层在1 mol/L Na2SO4溶液中的电化学阻抗谱(EIS)，较原始合金的容抗弧直径及|Z|值增加，相位角平台变宽，利用等效电路Rs-(Rt//CPE)拟合的激光熔凝层的极化电阻Rt由原始合金的13.8 kΩ·cm2增至38.7 kΩ·cm2，计算的有效电容CB则由32.5 μF/cm2降至19.7 μF/cm2。连续激光熔凝改性的Fe32Mn3Al7Cr反铁磁精密电阻合金的抗蚀性显著提高

Abstract:

The laser surface melting of an antiferromagnetic Fe32Mn3Al7Cr precision resistance alloy has been performed using a continuous CO2 laser, in order to improve the corrosion resistance. The microstructure, the phase structure, the microhardness and the corrosion property of the laser surface melted Fe32Mn3Al7Cr alloy were investigated. The laser surface melting layer was constructed by a fine equiaxed cellular crystal, a columnar dendritic crystal, and heat-effected matrix. A single austenite phase of the laser surface melting layer was obtained in the depth of about 650 mm. The microhardness of the laser surface melting layer was increased up to HV0.5 N 32 GPa from HV0.5 N 16 GPa of the austenite matrix. The anodic polarization behavior of the laser surface melting layers at the 100 μm and 350 μm depths, respectively, was evaluated in 1 mol/l Na2SO4 solution. Their self-passivation was observed instead of an active-passivation of the original alloy, with higher corrosion potentials of –420 mV(SCE) and –478 mV(CSE) and lower passive current densities of 1.3 μA/cm2 and 1.0 μA/cm2 than that of –658 mV(SCE) and 2.9 μA/cm2 for the austenite matrix. In 0.1 mol/l NaCl solution at pH=14, the laser surface melting layer exhibited an apparent improvement of the pitting corrosion resistance with no pitting corrosion. The electrochemical impedance spectroscopy (EIS) of the laser surface melting layer has the larger diameter of capacitive arc, the higher impedance modulus |Z|, the wider phase degree range, compared to that of the original alloy. The polarization resistant Rt of the melting layer fitted by using an equivalent electric circuit of Rs-(Rt//CPE) increased to 38.7 kΩ·cm2 from 13.8 kΩ·cm2 and the calculated effective capacitance CB decreased to 19.7 μF/cm2 from 32.5 μF/cm2. The laser surface melting led to a significant improvement of corrosion resistance of Fe32Mn3Al7Cr alloy