6063, 5005および7N01合金の接合界面の形成相に及ぼす接合温度の影響

透過電子顕微鏡観察によるAl合金の拡散接合機構の検討(第3報)

抄録

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 T_w ; i.e., Al₂MgO₄ and MgO at T_w <853 K, and MgO at T_w≥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.