Elemental diffusion, atomic substitution mechanisms and interfacial fracture behavior in laser welded–brazed Al/Ti

Abstract

Interfacial microstructure, fracture behavior, elemental diffusion, and Si atom substitution behavior were investigated in laser-welded–brazed Al/Ti joints. The results indicated that discontinuous intermetallic composite (IMC) and thick Ti(Al, Si) + Ti(Al, Si)2 + Ti(Al, Si)3 were generated under extremely low and high heat inputs, damaging joint strength. Interfaces with 1.02–3.20 μm Ti(Al, Si)3 was fractured at heat affected zone of Al and exhibited the highest strength of 252.0 MPa. Thermodynamic calculations indicated that elemental Mg and Si possessed lower chemical potentials at interface. This resulted in their aggregation at interface and formation of Mg2Si. Notably, the formation of Ti(Al, Si)3 acted as a barrier for further diffusion of Mg to IMCs. Density functional theory calculations were employed to clarify Si substitution behavior of Al. The calculated results indicated that smaller formation enthalpies and binding energies were obtained when Al atoms were substituted with Si atoms. Furthermore, the introduction of AlSi covalent bonds, lower total density of state (TDOS) values at EF level, and wider and negatively shifted pseudo-gaps contributed to a more stable structure and favored this substituted behavior. In addition, Si substitution would release charge accumulation level around the Ti atoms, resulting in a softening effect on the IMCs.