Microstructure And Bonding Mechanism Of Ti/Al Joint Using Argon Arc Welding-Brazing

Reactions between Ti and Al could produce kinds of brittle Ti-Al intermetallics at high temperature. Thermal joining of titanium to aluminum alloys using traditional fusion welding technologies is a challenge due to their great differences in physical-chemical properties. Welding wires SA11 100, SA14043, SA14047 and SA15356 were used to gas tungsten arc welding (GTAW) TA15/2024A1, TA15/5A06A1 dissimilar alloys in the paper. Influence of welding wire and aluminum base metal compositions on microstructures of the joints was studied. Microstructure of the joint is greatly influenced by the compositions of welding wire while seldom influenced by aluminum base metal. Only a few brittle precipitations were formed in the weld metal and the microstructure difference of Ti/Al transition region in thickness direction is relatively small using SA14047 wire. A large number of large-sized striped or bone-like precipitations were formed in the weld metal using other three kinds of wires and the microstructure difference of the transition region in thickness direction is large.Pulsed current gas metal arc welding (P-GMAW) of RuTi/1060Al dissimilar alloys was conducted using SA14043 wire. Influence of welding heat input on the joint microstructure was investigated. Microstructure of the weld metal and the Ti/Al transition region are greatly influenced by the variation of the welding heat input. Small granular or short rod-like precipitations were formed in the weld metal, a serrate reaction layer was formed adjacent to the Ti/Al interface with a relatively low welding heat input. Bulky striped and bone-like precipitations were formed in the weld metal and a multilayered transition region was formed adjacent to the Ti/Al interface with a relatively higher welding heat input.Phase constitutions of the Ti/Al transition region and element distribution near the transition region were investigated using SEM, EDS and XRD. The joining mechanism of Ti/Al dissimilar joint using Al-Si wires was studied. Titanium and aluminum dissimilar alloys were welded-brazed together using argon arc welding. Titanium and aluminum were mostly brazed together during the argon arc welding while slightly fusion welded in top surface of titanium alloy in GTAW joint. Intermetallics Ti3Al, TiAl+Ti5Si3 eutectic structure,TigAl23+Ti5Si3 eutectic structure (Ti5Al11+Ti5Si3 eutectic structure) and TiAl3 were formed as separated layers orderly from titanium side to weld metal in Ti/Al fusion zone. a-Ti,mixture of Ti5Si3 and TiAl3, TiAl3 were formed as separated layers from titanium side to weld metal adjacent to the Ti/Al brazed interface.Initiation and propagation of cracks in Ti/Al transition region were analyzed based on analysis of stress distribution.Both hot and cold cracks exist in Ti/Al transition region.Cold cracking took place in the fusion zone in the tail end of reinforcement at titanium side owing to residual stress perpendicular to top surface of titanium alloy, the cold cracks are prone to propagate along the interface between different intermetallics.Polygonization cracking initiated in Ti/Al fusion zone owing to the residual stress in horizontal direction, these hot cracks are prone to propagate along the polygonization boundaries that perpendicular to the titanium surface.The bond between titanium and weld metal is week in the joint root. Cold cracking initiated in the root due to the existence of residual stress, the cracks tends to propagate along the interface between titanium alloy and the interfacial reaction layer.Tensile strength of TA15/2014Al GTAW joints using SA14043 and SA14047 was evaluated using tensile test. In order to figure out the fracture behavior of the Ti/Al joint, morphologies of the fracture surface were analyzed using SEM. The ultimate tensile strength of Ti/Al joint using SA14043 wire is about 216 MPa. Most Ti/Al joints were fractured in titanium side while few failed in aluminum side. The joint mostly fractured along the interface between titanium and the reaction layer, however, a few regions fractured in the weld metal when failed in titanium side. The joint fractured in heat-affected zone of aluminum near the fusion zone when failed in aluminum side.All the joints were fractured near the Ti/Al transition region using SA14047 wire owing to the combination of tensile force and shear force, the strength of the Ti/Al joint was low.