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In this study, vanadium carbide (VC) was initially introduced into the molten pool using the cold wire method to refine the deposit grains and enhance the mechanical properties of arc direct energy deposition (ADED) aluminum alloy. Next, the grain structure's evolutionary behaviors and the second phase in the VC-strengthening ER5A06 aluminum alloy deposits were investigated, and the grain refinement mechanism was determined. The findings demonstrated that the cubic Al10V phase was produced after introducing VC, and the grain structure in the middle stable region of the building wall was transformed from coarse columnar grains (with an average size of 42.3 μm) into equiaxed fine grains (with an average size of 16.4 μm). Both Al10V and VC were coherent to α-Al in terms of orientation: (020)α-Al//(444)Al10V, [101―]α-Al//[112―]Al10V, and (111)α-Al//(111)VC and [011]α-Al//[011]VC. Their interatomic and interplanar spacing misfits were lower than 5 %, facilitating the heterogeneous nucleation of α-Al during molten pool solidification. Moreover, under multiple thermal cycles of ADED, the pinning effect of VC and Al10V effectively restricted the grain growth, thus enabling the building wall to steadily maintain a uniform, equiaxed, and fine-grained structure. Due to grain refinement and homogenization, the horizontal and vertical ultimate tensile strengths of the straight wall were improved by 16.8 % and 50.2 % (351.6 and 348.1 MPa), respectively, thereby eliminating the mechanical anisotropy. This work can provide a theoretical foundation and a novel method for the fine microstructure regulation and reinforcement of ADED aluminum alloy components. |
