Abstract
The effects of aluminum content in aluminum bronzes and bonding time on the joint strength of a commercial aluminum bronze and a stainless steel joints, which were bonded using the insert metal of Ni foil at the bonding temperature of 890°C, have been investigated. And also, Cu-Al binary alloys having various aluminum contents instead of the aluminum bronze were bonded to the stainless steel using Ni foil, in order to obtain the fundamental information of the diffusion layer, which affects the joint strength. The results obtained are as follows;
(1) In case of Cu-Al binary alloys, the phase of the diffusion layer that was formed on the Cu-Al alloy side of bonded zone was a solid solution of the Ni, Cu and Al in case of 2.13 wt% Al-Cu alloy, and κ phase (Ni3Al) in case of 4.52 wt%Al. β phase (Cu3Al+NiAl) and β+κ in case of 7.62 wt%Al.
(2) The joint strength depended on the aluminum content and the maximum joint strength of 427MPa was obtained in 3.51 wt%Al and the bonding time of 3.6ks, but the joint efficiency decreased as the aluminum content became higher.
(3) When the aluminum content was below 2 wt%, the fracture in tensile test occurred in the bronze of base metal up to the bonding time of 30 ks. As the aluminum content increased over 2 wt%, the fracture occurred in the diffusion layer and also the maximum joint efficiency was gradually shifted towared short bonding time.
(4) Kirkendall effect was recognized on the bonded interface between the bronze and the Ni foil, and the voids were formed in Kirkendall interface. These voids have acted as crack initiation sites.
(5) The number and size of voids in the diffusion layer increased as increasing the aluminum content, and also its size grew with the increase of bonding time.
(6) In case of 8.35 wt%Al, the fracture occurred from the void that was formed in the Ni foil instead of the void in the diffusion layer when bonding time was over 30 ks.
