Optimizing microstructure and minimizing defects in laser-arc hybrid additive manufacturing of Al-Cu alloy: The role of laser mode

Abstract

Recently, laser-arc hybrid additive manufacturing (LAHAM) has emerged as a transformative method for producing lightweight aluminum alloys, valued for its advantageous surface quality and mechanical properties. In this study, the effect of various laser modes on macro morphology, defect formation, microstructure evolution, and mechanical properties of Al-Cu alloy were investigated. At a laser power threshold of 1.5 kW, the transition from conduction mode to keyhole mode was observed. When the keyhole formed, the molten metal exhibited enhanced fluidity, resulting in smoother surfaces and more uniform spreading. As laser power increased, although hydrogen-induced pores (HIP) were notably reduced, the keyhole-induced pores (KIP) began to appear. During subsequent depositions, the intense reheating effects from laser facilitated a transformation from reticular eutectics (RE) along grain boundaries to granular eutectics (GE). Additionally, recrystallization and formation of Σ3 coincidence site lattice (CSL) boundaries were restricted due to the reduced residual stress caused by moderating cooling rates, alleviating stress concentration near pores during deformation. Therefore, optimal results were achieved in conduction mode at a laser power of 1 kW, achieving highest tensile strengths of 269.5 MPa and 260.1 MPa, and elongations of 19.6 % and 13.8 % in horizontal and vertical directions, respectively.