Effect of impurities in aluminum on the diffusion bonding of aluminum to titanium

Abstract

The joint strength and the microstructure of the diffusion bonding of aluminum to titanium have been investigated using a variety of base metals: commercially pure aluminum A1050 (6×10^-2mass%Si), nominally 99.99% (4N) aluminum (2×10^-3mass%Si), and aluminum alloys containing 1×10^-3 to 0.14mass%Si and 2×10^-3 to 0.38 mass%Fe. The joint strength of 4N aluminum to titanium, which was much lower than that of A1050 to titanium, was increased significantly by introduction of Si into 4N aluminum by a diffusion treatment prior to the bonding. A marker experiment showed that an intermetallic compound layer consisting of Al₃Ti grew from the bond interface into titanium for joints both with A1050 and with 4N aluminum. When the Si content exceeded 7×10^-3mass%, a drastic decrease in the growing rate of this Al₃Ti layer was found, suggesting that Si more than 7×10^-3mass% reduced the amount of aluminum diffusing into the Al₃Ti layer. The Fe content, however, had no correlation with the growing rate. The effects of Si on the joint strength and the growth of the Al₃Ti layer can be accounted for by the decrease in the amount of aluminum diffusing into the Al₃Ti layer.