1996 Volume 14 Issue 2 Pages 382-388
The behavior of the superficial oxide film at diffusion-bonded interfaces of Al alloys including Mg, Si, Cu, and Zn has been investigated by TEM observations to explain the effect of the alloying elements on the bondability of the Al alloy. Oxides remaining at the bond interface at bonding temperatures around 873 K could be classified by Mg content CMg : amorphous oxide films at CMg≤0.01%, crystalline particles of Al2MgO4 at 0.3%≤CMg<1%, and crystalline particles of MgO at 1%<CMg. The particles of Al2MgO4 and MgO were very fine about 10-100 nm in size. Alloying elements Si, Cu and Zn have only slight effect on the formation of crystalline oxide particles, but constituted precipitates which formed preferentially at the bond interface compared with the matrix and grain boundary. Precipitates observed were Mg2Si, CuAl2 and MgZn2, the size of which were very large compared with the crystalline oxide particles. The joint of the alloys with CMg≥0.3% had tensile strength significantly higher than those with CMg≤0.01%, suggesting that the morphology of the oxide is a controlling factor in the bond formation in the diffusion bonding of the Al alloy; i.e., the continuous oxide film is much more detrimental to the bond formation at the interface than the dispersed oxide particle.