| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 97 === Two topics including (1) the pre-immersion effect of heat-treated (i.e., T6, T73, RRA, OP1 and OP2) aluminum alloy 7050 on the stress corrosion cracking (SCC) in alkaline (pH=12) 3.5 wt% NaCl solution; and (2) the characterization of the Al-0.11 wt.% Sc sputtered films were concerned in this study. The effect of the pre-immersion on the SCC was investigated using slow strain rate test (SSRT) under electrochemical monitoring. The corrosion products on the specimens were analyzed through electron spectroscopy for chemical analysis (ESCA). It was found that pre-immersion enhances the SCC-resistance of the specimens, however, the enhancement varies with the type of heat treatments exerted to AA7050. The enhancement decreases in the order: T6 (43%) ＞ RRA (27%) ＞ OP1 (18%) ＞ OP2 (14%) ＞ T73 (11%). Analysis of the corrosion products revealed that they comprise elements such as Al, Zn, Mg, Cu and oxygen. Electron spectroscopy for chemical analysis (ESCA) of the corrosion product displayed that the content of copper hydroxide on T6 is stronger than on OP1 and RRA . Pre-immersion leads to the formation of CuO in the corrosion products of T6 and mixture of CuO and CuCl2 in the corrosion products of OP1 and RRA . The corrosion-resistant is much less for the mixture of CuO and CuCl2 than the monotonic the CuO.
A thin film of Al-0.11wt.% Sc was prepared by sputtering and its structure, characterizations (i.e., film adhesion, optical reflectivity and anti-corrosion behavior) concerned in the use of candidature reflector for the autolamp has been investigated and compared with the traditional pure Al-film prepared by thermal evaporation. The sputtered Al-0.11wt.% Sc film reveals better adhesion than the sputtered monotonic pure Al-film and than traditional evaporated pure Al-film. Through examination by atomic force microscope (AFM), the sputtered Al-0.11wt.% Sc exhibits better flatness and smoothness than the others thus displays higher optical reflectivity due to grain refinement in the film. Under long-term illumination, the films led to grain growth and hillocks formation. This grain growth and surface degradation caused by aged illumination severely decreased the reflectivity of the films, especially for the pure Al films. The sputtered Al-0.11wt.% Sc is more corrosion-resistant than the others in 5% NaCl solution regardless whether or not aged illumination.
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