The microstructure and mechanical properties of fluxless gas tungsten arc welding–brazing joints made between titanium and aluminum alloys

Abstract

Butt joining of a titanium alloy to an aluminum alloy by gas tungsten arc welding–brazing using an Al-Si eutectic filler wire without flux is investigated. The butt joints have dual characteristics, being a welding on the aluminum side and a brazing on the titanium side. The thickness of the reaction layer varies with position in the titanium alloy interfacial area of the joint, ranging from 2 to 5μm. At the upper part of interfacial area, the reaction layer includes only the rod-like TiAl3 phase with 10at.% dissolved Si. At the bottom of interfacial area, the reaction layer consists of the needle-like τ1 phases (Ti7Al5Si12) and the block-like TiAl3 phase. Hardness of the reaction layer near the welded seam/Ti alloy interface was as much as 400–500HV. The highest tensile joint strength observed was 158MPa. Tensile joint failure was by cracks initiating from the reaction layer at the bottom of the joint propagating into the welded seam at the upper part of the joint.