Microstructure and Tensile Property of Hybrid Fabricated Ti-6Al-4V Alloy by Investment Casting and Laser Additive Manufacturing

Abstract

Hybrid manufacturing of titanium alloys by investment casting and laser additive manufacturing (LAM) combines the advantages of both techniques and can further reduce the cost. In this study, microstructure evolution in the bonding zone and tensile property of the hybrid manufacturing Ti-6Al-4V alloy are carefully investigated. Results show that the hybrid sample consists of the LAM zone, the heat-affected zone (HAZ) and the base casting zone. A transition zone (TZ) forms within the HAZ close to the fusion line. Grains in the bottom of the LAM zone are much finer with a mixture of equiaxed grain and small columnar grain, and gradually coarsening to fully large columnar grains. Typical ultra-fine basket-wave microstructure forms in the LAM zone. In the TZ, the microstructure gradually changes from a fine basket-wave microstructure to a coarsened bimodal microstructure. The highest microhardness of the bonding zone is 491 HV. The fracture of the hybrid sample occurs in the casting half, and the tensile strength of the hybrid sample reaches (821 ± 31) MPa, which is higher than that of the pure casting sample ((778 ± 22) MPa). However, the elongation of the hybrid sample ((8.0 ± 0.5)%) is lower than that of the pure casting sample ((10.0 ± 1.7)%).