Spreading behavior and microstructure characteristics of dissimilar metals TIG welding-brazing of aluminum alloy to stainless steel

Dissimilar metals TIG welding-brazing of 5A06 aluminum alloy to SUS321 stainless steel had been conducted using 4047 Al-Si eutectic filler metal and modified non-corrosive flux. And spreading behavior of filler metal on the groove surface and microstructure characteristics of the butt joint were investigated. The spreading behavior of liquid filler metal consisted of two parts: one was to spread on the back face to pack the steel; the other was to uphill spread on the front face of the groove to form a sound brazed seam. The interfacial layer, unequal in thickness at different position, ranged from 5 μm to 35 μm. And it was made up of three different kinds of IMC layers: from the welded seam to stainless steel, the first was τ5-Al7.2Fe2Si and α-Al phases, the second was η-Fe2Al5 phase, and the third was FeSi2 and η-Fe2Al5 phases. Average tensile strength of the butt joint reached 120.0 MPa and fracture occurred at the interfacial layer. Cracks derived from the top part of brittle η-Fe2Al5 interfacial layer when its thickness exceeded 10 μm.