The influence of building parameters on residual stress, interfacial structure, and cracking control of laser powder bed fusion processed Ti6Al4V/AlMgScZr multi-material parts

Abstract

With the growing demand for lightweight and high-performance components applied in extreme aerospace environments, there is a prospective interest in producing the integrated multi-material components consisting of titanium alloy and aluminum alloy. Laser powder bed fusion (LPBF), as a laser powder bed based additive manufacturing process with a high production flexibility, shows a promising potential in creating multi-material components. However, due to the possibility of the generation of various intermetallic compounds (IMCs) at the interface, it has been a significant challenge to fabricate reliable Ti/Al alloy multi-material components without any crack formation by LPBF. In this study, the Ti6Al4V/AlMgScZr multi-material parts were fabricated by LPBF and the effects of building parameters of AlMgScZr on the residual stress and crack control of Ti6Al4V/AlMgScZr multi-material parts were investigated. The evolution mechanisms of IMC phases at the interface under laser interaction were further revealed. Due to the change of elemental compositions and difference in Gibbs free energies of IMCs, a gradient ordered transition zone with a width of about 450 μm consisting of Al3Ti, TiAl, and Ti3Al was formed from AlMgScZr to Ti6Al4V. A finite element model was established to explain the effects of process parameters on residual stress evolution, cracking formation and its control. As the scan speed increased from 500 to 1100 mm/s and the attendant building height of AlMgScZr increased to 60 layers, the residual stress of laser processed Ti6Al4V decreased from 439 to 364 MPa, but the residual stress of AlMgScZr increased from 195 to 303 MPa. As the applied scan speed was enhanced to process AlMgScZr, the element diffusion was mitigated, thereby reducing the formation of IMCs and stress concentration. This study shows the possibility of in-situ control of IMCs and residual stress by process optimization during LPBF preparation of titanium alloy/aluminum multi-material parts without crack formation.