Realization of synergistic enhancement for fracture strength and ductility by adding TiC particles in wire and arc additive manufacturing 2219 aluminium alloy

Abstract

TiC reinforced Al-matrix composites were fabricated by wire and arc additive manufacturing (WAAM) method. The effects of TiC content on the evolution of grain boundary structure, phase transformation, grains distribution, interface mismatch, and mechanical properties of the WAAM-deposited 2219 Al–Cu alloys were investigated. The columnar grains in the inner-layer zone were transformed to equiaxed grains by the addition of TiC particles, which eventually induced the decrease of free energy for the Al-matrix, promoting an opportunity for nuclei to grow on the TiC substrate. TiC particles played an important role in generating the nucleation supercooling (ΔTns, 3.8 °C), multi-site heterogeneous nucleation with a lower value of ΔTns inhibited the constitutional supercooling (ΔTcs) caused by segregation of Cu. The degree of grain boundary segregation was greatly weakened, and the α-Al+θ-CuAl2 phase was semi-coherent with the matrix at the grain boundary, i.e. [1–31]Al2Cu//[0–11]Al, (211)Al2Cu//(100)Al. The fine spot-like phase possessed a strong interfacial bonding with the Al-matrix. The Al2Cu and TiC possessed a coherent interface with crystal orientation relations, i.e. [00–1]TiC//[01-1]Al2Cu, (110)TiC//(100)Al2Cu. Besides that, the fine spot-like phases and the well-dispersed TiC particles within the grains promoted the formation of dislocations. Therefore, the strength and toughness of the deposited 2219 alloy were improved synergistically. Eventually, the deposited sample exhibited a tensile strength around 384 MPa, and the elongation was up to 18.3%.