1996 Volume 14 Issue 2 Pages 389-397
The effects of the bonding temperature on the interfacial phase and bond strength of diffusion-bonded joints have been investigated mainly by TEM observations for commercial aluminum alloys containing Mg: Al-Mg-Si alloy 6063 (0.5%Mg), Al-Mg alloy 5005 (0.8%Mg), and Al-Zn-Mg alloy 7N01 (1.15%Mg). At the bond interfaces of these alloys, amorphous oxide films were observed, which altered gradually to crystalline oxide particles, as the bonding temperature was increased. The bonding temperature at which the amorphous oxide film disappeared lowered with increasing the Mg content. As the area occupied by the amorphous oxide film on the bond interface was decreased, the tensile strength of the joints of all the alloys increased significantly, suggesting that the amorphous oxide film was a major factor interfering with the increase in the bond strength. The crystalline oxides at the bond interfaces of 6063 and 7N01 alloys were identified as Al2MgO4 and MgO at all bonding temperatures employed, respectively. In contrast, at the bond interrf ace of 5005 alloy, both the crystalline oxides were observed depending on bonding temperature Tw ; i.e., Al2MgO4 and MgO at Tw <853 K, and MgO at Tw≥853 K. In addition, particulate intermetallic compounds much larger than the oxide particles were precipitated preferentially at the bond interface (Mg2Si for 6063 alloy joints and MgZn2 for 7N01 alloy joints). Although these intermetallic compounds precipitated at the bond interface seem to act an initiation site of dimples on the fractured surface, they can be considered to have much less influence on the bond strength than the amorphous oxide film, since solution treatments for dissolving these precititates resulted in only slight improvement in the tensile strength of joints.
