Dissimilar Spot Forge-Welding of Pure Titanium TP270 and Aluminum Alloy AA6061

Abstract

The spot forge-welding method, which has been recently proposed to enable high-productivity joining of high-strength dissimilar materials, was used to lap-join plates of pure titanium TP270 and aluminum alloy AA6061. The relationship between the processing condition and the joint strength was investigated, along with the texture of the bonded interface (BI). The tensile shear load of the joint increased rapidly with increasing reduction ratio or press peak pressure. The transition condition from BI fracture to base-metal (BM) fracture was not affected by the weld diameter, whereas the joining temperature had a strong effect. A lower joining temperature was associated with greater plastic flow requirement for BM fracture. Fatigue testing and analysis of the BI were performed to compare the results of tensile shear testing under two conditions: one in which the BI fractured (bonding temperature: 543 K) and one in which the BM fractured (bonding temperature: 623 K). At the bonding temperature of 543 K, the BI fractured in the high-cycle fatigue region. However, at the bonding temperature of 623 K, all fractures occurred on the Al alloy BM side. At the bonding temperature of 543 K, a very thin reaction layer (RL) with thickness of several nanometers was observed; at the bonding temperature of 623 K, an RL with thickness of approximately 30 to 100 nm was observed, which was identified as TiAl₃.