Effects of Si additions on intermetallic compound layer of aluminum–steel TIG welding–brazing joint

Dissimilar metals of 5A06 aluminum alloy and AISI 321 stainless steel were butt joined successfully by TIG welding–brazing with 1100 pure Al, 4043 AlSi5 and 4047 AlSi12 filler metals. Si additions in the filler metal have great effects in preventing the growth of the IMC layer, and minimizing its thickness. The joint interface with pure aluminum consists of the θ-FeAl 3 in aluminum side and η-Fe 2Al 5 in steel side, while the interfaces with Al–Si filler metals are the τ 5-Al 7.2Fe 1.8Si in aluminum side and θ-Fe(Al,Si) 3 in steel side. And with 5 wt.% of Si additions, the IMC layer has the optimum mechanical properties, and the tensile strength of the joint reaches 125.2 MPa. The growth mechanism of the IMC layers is controlled by the dissolution and diffusion of Fe atoms in the liquid. At the same time, Si atoms aggregate in the interface and participate the IMC layer's formation.