Experimental investigation of butt welded Ti/steel bimetallic sheets by using multi-principal powders as a single filler metal

Abstract

Owing to the easy-to-crack in the weld zones (WZ) of titanium alloy/steel bimetallic sheets, sequentially layered-to-layered welding, by using various filler metals, is widely adopted to join the bimetallic sheets. In this study, multi-principal filler powders of FeCoCrNiMn, as only one type of filler metal, were used to join TA1/Q345 bimetallic sheets by laser deposition welding. Microstructure evolution, microhardness, and tensile properties in the joint of TA1/Q345 bimetallic sheets were studied. The results indicated that TA1/Q345 bimetallic sheets could be joined by using multi-principal filler metal when the groove root was opened in the Q345 base plate. Significant transition zones were found at the TA1/WZ and Q345/WZ interfaces. The structures of α-Fe, β-Ti, β-Ti + TiFe, and α-Fe + TiFe2 were formed in the transition zones. The solidified primary phases of TiFe2 and the eutectic structures of α-Fe + TiFe2 were observed in most regions of the WZ. Various intermetallic compounds (IMCs) of TiFe and TiFe2, as well as the snowflake-like structures of TiC, coexisted in the WZ near the flyer and base layers, which were significantly harmful to the formability of the WZ and caused a crack in the WZ. The markedly high hardness and low tensile strength were presented in the WZ. A sawtooth-like fracture line was observed. The fracture line was extended from the WZ/base metal (BM) interface to the WZ center, in which the minimum hardness (∼523 HV0.2) and many eutectic structures were presented.