Refinement of second-phase particles and grain structures of 2219 Al[sbnd]Cu alloy forgings using an improved thermomechanical treatment process

Abstract

2219 AlCu alloy components are conventionally fabricated by multiaxial hot forging, but they often contain coarse second-phase particles and grain structures. In this work, an improved thermomechanical treatment process involving multiaxial hot forging, multiaxial cryoforging, and T8 heat treatment (i.e., solid solution, pre-deformation, and artificial aging), was used to refine the coarse microstructures of 2219 AlCu alloy. The microstructure evolution during this process and its effect on the mechanical properties were studied. The results show that the second-phase particles experienced limited break-up during multiaxial hot forging but were significantly broken into finer particles during multiaxial cryoforging. Particle fragmentation gradually increased upon increasing the number of cryoforging passes, which increased the particle/matrix interfacial energy. Meanwhile, ultrafine-grain structures and high dislocation density were formed in the cryoforged sample after six passes, which increased the driving force for recrystallization and thus the number of nucleation sites in the material. Consequently, the grain size decreased to 18.9 μm compared with the 29.5 μm grain size of the sample obtained in one pass after T8 heat treatment. The smaller particle size and increased number of grain boundaries promoted the dissolution of second-phase particles, which increased the density of precipitates during subsequent artificial aging. As a result, the forging obtained by the thermomechanical treatment displayed good mechanical properties, with a yield strength of 375 MPa, ultimate tensile strength of 473 MPa, and elongation of 16.3%.