Realization of structural evolution in grain boundary, solute redistribution and improved mechanical properties by adding TiCnps in wire and arc additive manufacturing 2219 aluminium alloy

Abstract

Non-equilibrium solidification and experienced thermal conditions of deposited 2219 aluminium alloy during wire and arc additive manufacturing (WAAM) result in the grain boundary segregation, which makes it difficult to avoid the appearance of columnar grain. In this work, columnar crystal defects and grain boundary segregation were eliminated by adding TiC nanoparticles (TiCnps) to WAAM-deposited 2219 aluminium alloy. The effects of TiCnps addition on the solidification dynamics, particles distribution, grain boundary structure, solute redistribution, and mechanical properties were investigated. The solidification dynamics of the droplet induced by mesoscopic TiC particles was assessed and the result showed that the addition of c. 80 nm TiCnps could reduce the solid–liquid growth rate (R), besides, the critical movement rate (Rc) of 80 nm TiCnps was much lower than that of R, i.e. TiCnps were inclined to be distributed inside the grains as effective nucleation particles. Micro-pools with multi-site nucleation inhibited grain boundary segregation and increased Cu concentration in Al-matrix. Such a variation in Cu atom concentration promoted the precipitation of the fine spot-like θ′-CuAl2 phase with a diameter of c. 500 nm, besides, the dendritic θ-CuAl2 phase along the grain boundary was all transformed into α-Al+θ-CuAl2 phases with a semi-coherent state. The fine spot-like phase and TiCnps possessed a strong interfacial bonding with the Al-matrix, thereby the mechanical properties of the deposited 2219 aluminium alloy were strengthened. Eventually, the deposited 2219 aluminium alloy with the addition of TiCnps exhibited excellent mechanical properties, i.e. the tensile strength of the samples were around 380 MPa, and the elongation could be up to 21.4%.