晶界特征对7020铝合金腐蚀行为的影响

研究了不同晶粒组织的7020铝合金挤压型材表层和中心层的腐蚀性能变化规律。利用透射电子显微镜分析了不同晶界的析出特征，并根据相邻晶粒的选区电子衍射花样计算了晶界取向差，建立了晶界取向差与晶界析出特征之间的定量关系。结果表明: 大角度晶界上的析出相尺寸、间距以及无沉淀析出带(PFZ)宽度均大于小角度晶界上的。小角度晶界上的析出相尺寸和PFZ宽度随晶界取向差增加而增加。含较高小角度晶界比例的中心层试样比表层试样的局部腐蚀抗性更好，由表层至中心层，小角度晶界比例增加了30.04%，晶间腐蚀最大深度从22.67 μm降至2.80 μm，剥落腐蚀最大深度从436.52 μm降至353.01 μm。

Effect of Grain Boundary Characteristics on Corrosion Behavior of 7020 Aluminum Alloy

The corrosion behavior of the surface and center layer of extruded profile of 7020 aluminum alloy with different grain structures was investigated. The precipitation characteristics of different grain boundaries were analyzed by transmission electron microscope, and the grain boundary misorientation was calculated according to the electron diffraction patterns of selected area in adjacent grains. Then, the quantitative relationship between the grain boundary misorientation and the grain boundary precipitation characteristics was established. It is found from the study that the size and spacing of the grain boundary precipitates and the width of precipitates free zones (PFZ) in high-angle grain boundaries are much larger compared to low-angle grain boundaries. The size of the grain boundary precipitates and the width of PFZ in low-angle grain boundaries all increase with the increase of the grain boundary misorientation. The sample of center layer with higher frequency of low-angle grain boundaries has a better local corrosion resistance compared to the sample of surface layer. From the surface layer to the center layer, the frequency of low-angle grain boundaries increases by 30.04%, the maximum depth of intergranular corrosion decreases from 22.67 μm to 2.80 μm, and the maximum depth of exfoliation corrosion decreases from 436.52 μm to 353.01 μm.