| Summary: | 博士 === 國立中興大學 === 材料科學與工程學系 === 96 === Abstract
The purpose of this dissertation was undertaken to investigate the effect of gallium on the liquid metal embrittlement of aluminum alloy. This work was conducted to develop a pragmatic and satisfactory procedure to promote intergranular cracking for ductile AA6061 Al-Mg-Si alloy at room temperature. The study was also consider the various amount of Ga, holding temperatures and the sample with various rolling directions on the severity of liquid metal embrittlement, respectively. In addition, there remain uncertainties as to the magnitude of the grain boundary chemical composition of AA6061 samples induced by the embrittling agents and its effects on intergranular fracture. To answer these questions, AA1050 sample was used for comparison to determine whether alloying elements would correlate with Ga-induced embrittlement that governed the occurred of intergranular fracture in the AA6061 sample.
According to the SEM observation, the ductile fracture from the samples without any Ga applied on them was observed. The almost fracture surface of samples with Ga was found to be predominantly intergranular. However, intergranular fracture of samples did not occur when the amount of Ga in contact with the sample was less than a critical value. The results proved that the amount of Ga clearly affected the degree of embrittlement of aluminum alloy. The tensile test results showed that the tensile load of Ga-treated sample was significantly higher than that of the samples without any Ga applied on them. When the Ga applied to the samples, the tensile properties of these samples markedly deteriorated. The tensile load and the ratio of dimpled area for the AA6061 sample declines as the amount of Ga applied on them increases. The AES peak-to-peak ratio IMg/IAl showed that the magnesium enrichment on grain boundary is associated with the rolling direction of the sample. Mg enrichment on grain boundaey boundary in the sample whose longitudinal axis was parallel to the rolling direction is relatively weak. A high peak intensity of Mg was observed in the sample whose longitudinal axis is perpendicular to the rolling direction. The AES results also showed that the enrichment of Mg on the grain boundary does not follow from oxidation of the intergranular fracture surface, even though Mg has a high affinity for O. The AES depth profiles indicated that Ga affected the depth profiles of Mg, Al, and O from the surface to the interior. The Mg profile showed a decreasing tendency from the surface to the interior of the sample. In contrast to the Mg profile, the concentration of Ga had a rapid increase from the surface to interior. The reason of embrittlement of Ga-treated AA6061 and AA1050 samples was compared with that of AA1050 sample. The embrittlement of the AA6061 samples with Ga involves a combination of the following two effects: Ga metal on grain boundary embrittlement, and Ga-induced Mg enrichment on grain boundary that further decreases the strength of the grain boundary. However, the behavior of embrittlement of AA1050 sample was occurred due to one of Ga on grain boundary.
In this dissertation examines the effect of Ga on liquid metal embrittlement of aluminum alloys. It provides a new method for fracturing the sample intergranular at room temperature. Moreover, this dissertation was also explained that the amount of Ga, holding temperature and the samples with various rolling directions on the severity of liquid metal embrittlement.
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