Grain refinement and β phase redistribution of Al-Mg alloy induced by bimodal-sized TiB2 particles synergistic interaction prepared by wire-arc directed energy deposition

The distribution and morphology of beta phase (Al3Mg2) in the microstructure are directly linked to the mechanical properties of Al-Mg alloys, including hardness, tensile properties and corrosion resistance. In this study, an additive manufactured bimodal-sized TiB2/Al-Mg composite was fabricated using the cold metal transfer (CMT) process. This composite shows impressive hardness at 80 HV, significantly surpassing that of its wrought matrix counterparts, along with a tensile strength of 284.4 MPa and a non-reduced elongation of 23 %. The superior mechanical properties can be attributed to a unique microstructure, characterized by refined equiaxed grains, numerous nano-cells in grains, and a dispersed distribution of beta phase. The synergistic effect of bimodal-sized TiB2 during the non-equilibrium solidification process promotes nucleation while effectively suppressing grain growth. In addition, the increased nucleation interfaces provided by refined grains and nano-cells containing nano-sized TiB2 significantly disrupted the continuous distribution characteristic of the beta phase along grain boundaries. The high-density dislocations introduced by the addition of these particles influenced the diffusion behavior of solutes, leading to the dispersed distribution of the beta phase.