Behavior of Oxide Film in Diffusion Bonding of Aluminum(Materials, Metallurgy & Weldability)
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The microstructure of bond interface in the diffusion-bonded joint of aluminum has been investigated with transmission electron microscope (TEM) in order to obtain a direct evidence for the existence of aluminum oxide which originates from oxide films on faying surfaces. The effect of the state of faying surface on the morphology of the oxide has also been examined using faying surfaces subjected to the following three treatments: (i) wire brushing, (ii) electropolishing subsequent to grinding on 1200 grade emery paper, and (iii) electropolishing subsequent to wire brushing. Results obtained are summarized as follows: The oxide was found at the bond interface for all the surface treatments (i), (ii) and (iii). However, the morphology and distribution of the oxide were strongly influenced by the surface treatments. When the faying surface subjected to the treatment (i) was used, a number of oxide particles were distributed within a zone about 1 to 3μm in thickness along the bond interface. The zone was found to consist of many small grains less than 1μm in diameter. The formation of this zone is ascribed to a surface layer into which a significant degree of cold working and a lot of oxides are introduced during the wire brushing. The zone involving the oxide had harmful effects on the bond strength, because the surface treatment (i) led to a much lower bond strength than the treatment (ii) and (iii). On the other hand, when faying surfaces subjected to the treatments (ii) and (iii) were used, the oxide was observed only along the bond interface as a thin film about 30 to 40nm in thickness. The proportion of the bond interface where the oxide was broken up was larger when faying surfaces were subjected to the treatment (iii) than the treatment (ii), and so a higher bond strength was obtained by using the treatment (iii) than the treatment (ii).
- Transactions of JWRI
Transactions of JWRI 14(1), 115-122, 1985-07