采用交变电场脉冲钝化技术表面改性Fe24Mn4Al5Cr反铁磁定膨胀合金. 在1.0 mol/L Na₂SO₄溶液中通过脉冲钝化生长钝化膜, 再在1.0 mol/L Na₂SO₄+0.5 mol/L Na₂SO₄溶液中测定电位衰减曲线, 以优化脉冲钝化工艺参数. 利用AES和XPS分析优化工艺条件下生长的脉冲钝化膜化学组成、键合状态及其深度分布; 利用阳极极化曲线和电化学阻抗谱测试脉冲钝化膜耐腐蚀性能, 并与直流 620 mV连续钝化15 min生长钝化膜相比较. 研究发现, 脉冲钝化膜中元素Al和Cr富集, 元素 Mn贫化, 具有保护性的Al₂O₃和Cr₂O₃氧化物阻碍层增厚. 脉冲钝化膜的阳极极化曲线呈自钝化, 自腐蚀电位E_corr
由连续钝化膜的-360 mV增至-100 mV, 维钝电流密度em_p由 2.6 μA/cm²降至0.7 μA/cm², 阳极极化性能与AISI 304不锈钢相当. 脉冲钝化膜的EIS与连续钝化膜相比, 其容抗弧直径及|Z|值增加, 相位角平台变宽, 利用等效电路R_s-(R_p//CPE)拟合的脉冲钝化膜电阻R_p由连续钝化膜的14.8 kΩ·cm²增至54.0 kΩ·cm^2, 计算的有效电容C_B则由14.0 μF/cm²降至10.2 μF/cm². Fe24Mn4Al5Cr反铁磁定膨胀合金脉冲钝化膜的绝缘性提高, 耐蚀性改善.

An antiferromagnetic Fe24Mn4Al5Cr covar alloy has been impulse-passivated by an alternating current (AC) voltage overlapping a direct current (DC) voltage, in order to improve its corrosion resistance due to the poor corrosion property of austenite matrix with a high Mn content, a low Cr and/or Al content. The impulse-passivated films were obtained in 1.0 mol/L Na₂SO₄ solution at an AC voltage with modulation amplitude of 180-480 mV during alternating period of 200-400 ms for modification time of 5-15 min, and simultaneously at a DC voltage of 620 mV. The impulse-passivation parameters in 1.0 mol/L Na₂SO₄ + 0.5 mol/L Ha₂SO₄ solution were optimized as amplitude of 380 mV, period of 300 ms, and time of 10 min, by using the potential decline curves. The impulse-passivated films on the covar alloy under the optimum parameters were characterized by Auger electron spectroscopy and X-ray photoelectron spectroscopy (AES/XPS), and evaluated by anodic polarization and electrochemical impedance spectroscopy (EIS), respectively, and compared with those of the constant-passivated films at DC voltage of 620 mV for modification time of 15 min. In the impulse-passivated films on the covar alloy, an enrichment of elements Al and Cr, a lack of Mn in a thick barrier film composed of oxides Al₂O₃ and Cr₂O₃. The anodic polarization curves of the impulse-passivated films have a self-passivation with the higher corrosion potential of -100 mV and lower passive current density of 0.7 μA/cm², than those of -360 mV and 2.6 μA/cm² for the constant-passivated films. These electrochemical polarization behaviors were similar to those of the AISI 304 austenitic stainless steel. The EIS of the impulse-passivated films has larger diameter of capacitive arc, higher impedance modulus $|Z|$, and wider phase degree range,  relative to the constant-passivated films. Correspondently, the impulse-passivated film resistant R_p increased to 54.0 kΩ·cm² from 14.8 kΩ·cm² and effective capacitance decreased to 10.2 μF/cm² from 14.0 μF/cm², using an equivalent electric circuit of< R_s-(R_p//CPE). The high insulation of the impulse-passivated films on the covar alloy led to an improved corrosion resistance of the cover alloy. The impulse-passivated antiferromagnetic Fe24Mn4Al5Cr covar alloy exhibits an application potential in wide industrial field.