Investigations on the Interface Microstructure of Stainless Steel/Aluminum Joints Created by the Surface Activated Bonding Method

Stainless steel and aluminum have been bonded by the surfaceactivated bonding method. Both transmission electron microscopy (TEM)and scanning electron microscopy (SEM) have been used to investigatethe interface microstructure of the as-bonded and annealed joints. Aperfect interface did not show any microcracks or porosity for theas-bonded joints. An 10 nm thick intermediate layer composed ofmainly silicon and certain amounts of oxygen and carbon was foundbetween stainless steel and aluminum by means of high resolutionelectron microscopy (HRTEM). The interface morphology of the jointsvaried gradually as the bonded joints are heated at elevatedtemperature. When heated to 573 K, individual precipitate-likefluctuation at the interface area was detected, with slightmodification of the interface morphology. Bulky intermetalliccompounds finally formed throughout the original interface boundarywhen heated to 873 K and contributed to the weakening of theinterface boundary of the joints.