超声滚压对6061铝合金晶间腐蚀行为的影响

Effect of Ultrasonic Rolling on Intergranular Corrosion Behavior of 6061 Aluminum Alloy

目的 研究不同静压力条件下形变诱导梯度变形层对6061铝合金晶间腐蚀行为的影响。方法 使用超声滚压技术(USRP,Ultrasonic surface rolling processing)强化6061铝合金表层,采用激光共聚焦、X射线衍射等方法研究酸化Na Cl溶液体系下3种静压力条件对6061铝合金晶间腐蚀行为的影响。结果 随着静压力的增大,6061铝合金表层组织呈梯度变化,且形变层深度可延伸至近300μm。在酸化NaCl溶液腐蚀加速条件下,在相同时间内滚压后试样沿晶腐蚀的路径大幅缩短,向下扩展的深度降低了50%,使得6061铝合金的抗晶间腐蚀性能显著提高。表征结果表明,晶间腐蚀扩展路径与表面粗糙度无相关性,它主要与第二相(AlFeSi相)在形变层中的弥散分布有关。未经USRP处理的6061铝合金在沿晶界连续分布的AlFeSi相促进下发生了明显的沿晶腐蚀。相比之下,经USRP处理后,AlFeSi相会因晶粒形变而呈断续分布,减弱了它在晶界区域对铝合金基体的电偶腐蚀作用,降低了腐蚀通道的连通性,从而阻碍了腐蚀路径的扩展。结论 USRP可提高6061铝合金的抗晶间腐蚀性能,其表面粗糙度并非是提高晶间腐蚀抗性的主要因素,经USRP细化和分散后的AlFeSi相是阻断沿晶腐蚀路径的关键因素。

The work aims to study the effect of the deformed layer on intergranular corrosion of 6061 aluminum alloys under three static pressure conditions.In this paper,USRP(ultrasonic surface rolling processing) was adopted to strengthen the surface layer of 6061 aluminum alloys,which was characterized with a scanning electron microscopy,a laser confocal microscopy,X-ray diffraction,et al.Under three kinds of static pressures,the results showed that after ultrasonic surface rolling processing(USRP),the cross section generated deformed layer which refined and elongated grains on the top surface,the length of deformed layer extended to three hundreds microns,and the corrosion channel was blocked and the expansion depth was reduced to fifty percent under the accelerated corrosion condition with the acidified NaCl solution.The intergranular corrosion susceptibility was reduced by ultrasonic surface rolling processing.However,the characterization results performed that the material hardness decreased gradually with the increase of depth which stayed away from the surface.It was worth noting that the region of hardness was not in consistent with the deformed layer by optical microscope.So,it was concluded that the intergranular corrosion propagation path did not have a primary relationship with surface roughness,which was mainly related to the dispersion distribution of AlFeSi phase in the deformed layer.The fined level depended on the pressure,which was a positive correlation.The results suggested that the corrosion path of untreated samples extended along a certain grain boundary which was filled the second phase as the cathode phase.The grains of the cross section fell off,and the corrosion behavior transformed from the intergranular corrosion to exfoliation corrosion,which presented a deep corrosion path from the top surface and a narrow corrosion width by the scanning electron microscope and the laser confocal microscope.That because the dispersed second phase broke off the continuity of the electrochemical micro couples in the treated alloy eventually,which made the corrosion depth shorter and the corrosion path wider than those of the untreated sample.Moreover,when the AlFeSi phase was refined under different pressures in the matrix,after the ultrasonic surface rolling processing,the damage mode did not change from intergranular corrosion to exfoliation corrosion with the increase of pressure.The corrosion scope of the matrix became smaller,and the decrease intergranular corrosion susceptibility of the alloy was significantly increased.The brittle phase of AlFeSi phase was elongated and broken along the rolling direction.Compared with the untreated samples,after the intergranular corrosion test time of three hours,the AlFeSi phase affected corrosion processing,and the dispersion distribution of the AlFeSi phase destroyed the galvanic corrosion with the surrounding matrix.These results show that USRP can improve the intergranular corrosion resistance of 6061 aluminum alloy.The surface roughness is not the main factors to improve the intergranular corrosion resistance.However,refining and dispersing the AlFeSi phase in 6061 aluminum alloy through USRP is the key factor to inhibit the intergranular corrosion extension.