Gallium-induced magnesium enrichment on grain boundary and the gallium effect on degradation of tensile properties of al
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GALLIUM (Ga) is important for use in the semiconductor industry. III-V semiconductors such as GaAs are used in a wide variety of optoelectronic equipment.[1] Furthermore, Ga can be used as a substitute for mercury in hightemperature thermometers, and as a coating for mirrors.[2] Also, it is used as a lubricant for high current-density brushes.[3] Manufacturing processes devoted to the fabrication of GaAs-based semiconductor devices generate large volumes of waste that contain the toxic metal arsenic as well as Ga.[4,5] Manufacture or discarding of Ga-related products may lead to an excess of Ga discharging into the environment. According to Izumi,[5] the exhaust of Ga from the toxic wastes of the semiconductor industry will be a major problem in the near future. The environmental impact of the semiconductor and optoelectronic industry is therefore an important issue.[5,6] Although levels of Ga tolerance in humans are still being studied,[7] Ga is remarkable for its ability to penetrate the atomic lattices of other metals, resulting in severe embrittlement at grain boundaries.[2] However, earlier studies[8,9,10] have focused on the effect of Ga on the embrittlement of ductile alloys (e.g., aluminum and its alloys) when stressed in contact with a well-supplied liquid Ga. There are limited reports concerning the effect of a trace amounts of Ga on the embrittlement of ductile materials. Currently, aluminum and its alloys are widely used in building, construction, transportation, etc.[11] JUN-YEN UAN, Assistant Professor, and CHENG-CHIA CHANG, Graduate Student, are with the Department of Materials Engineering, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung 402, Taiwan, R.O.C. Contact e-mail: [email protected] Manuscript submitted October 26, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
Therefore, the effect of trace amounts of Ga on the embrittlement damage of Al alloys is an important topic that will be explored in the present study. Our previous study[12] showed that a trace amount of Ga being applied on an AA6061-T4 sample at room temperature can make the sample fracture intergranularly, yielding an clean intergranular fracture surface free of Ga film. Although the findings suggest Mg segregation on the grain boundary of the AA6061 alloy after T4 treatment, the intensity of Mg on the grain boundary is evidently higher than that of Al.[12] This result implies that the Ga atoms diffused to the grain boundary may affect the Mg concentration at the grain boundary, because AA6061 alloy contains only ;1 wt pct Mg. Mg is one of the most important alloying elements in aluminum alloys. The grain boundary segregation of Mg on water-quenched Al-Zn-Mg alloy from their solution treatment temperature has been suggested as one of the major factors making them prone to premature failure.[13,14] Therefore, the effect of Ga on grain boundary chemical compositions of the 6061 Al-Mg-Si alloy should be further explored. To detect the grain boundary chemistry of a Al-Mg-Mn alloy, Vetrano et al.[15] used liquid Ga to
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