| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 87 === Electrochemical techniques were used to investigate the corrosion behavior of stressed aluminum in phosphoric acid containing citric acid solution. Two kinds of approaches including tension and wear were analyzed. In the first part, the anodic dissolution behaviors of stressed aluminum were determined, including passive film breakdown. In the second part, the specimens were worn in the electrolyte and the electrochemical behaviors and the synergistic effects between mechanical and chemical interaction of aluminum under various abrasive conditions were also estimated.
The results show that the anodic current densities of stressed aluminum are higher than unstressed ones in electrolyte. However, in plastic region, the effects of stress on anodic current are indistinctive. In scratch test, the current and potential were monitored during test to identify the effects of passive film breakdown. The results exhibit that both of current and potential vibrate with scratch applied, then reduced to the initial value rapidly. It indicates that the fresh surface is passive again in electrolyte quickly. In the potential pulse test, the fresh surface also reacts with electrolyte to form oxide layer and then inhibits the following dissolution. Thus, the current densities decay with time immediately.
The results of wear-corrosion tests show that the corrosion potentials decrease with increasing stress and rotation speed. The quasi-passive behaviors are observed in anodic polarization curves. Furthermore, the calculated corrosion current densities increase linearly with mechanical variables. The weight loss of wear corrosion is mainly contributed from mechanically removed. The weight loss of mechanical wear, which is obtained under cathodic protection, is larger than the weight loss of wear corrosion. However, the chemical dissolution weight is much less than the weight loss of mechanical wear.
The micrographs of SEM observations demonstrate that the worn surface with ripple edges of layer structure is destroyed in ductile fracture. The similar micrograph is also found in the abrasive alumina bulk. Tribochemical reaction is the primary fracture mechanism in this study. The removed material, which is small particles of aluminum, will dissolve to electrolyte gradually.
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