Microstructure and mechanical properties of AlSi10Mg alloy built by laser powder bed fusion/direct energy deposition hybrid laser additive manufacturing

Abstract

Laser-based metal additive manufacturing technology, which is represented by laser powder bed fusion (LPBF) and direct energy deposition (DED), has been widely used in high-end industries such as aerospace. However, with the rapid development of aerospace equipment, it has become increasingly difficult to meet the requirements of integrated design and manufacturing of metal parts by using LPBF or DED alone. LPBF/DED hybrid laser additive manufacturing technology is expected to greatly improve the overall manufacturing capacity of metal components by combining the advantages of the two technologies. It is expected to break through the limitation of overall manufacturing size, to realize the manufacturing of large and complex aerospace parts, and to reduce the number of components required for large and complex structures to meet the overall design and manufacturing requirements. In this paper, AlSi10Mg was selected as the build material for the LPBF/DED hybrid laser additive manufacturing process and the microstructure and mechanical properties of the as-built samples were studied. The analyses of the microstructure show that there are no obvious defects at the interface between the LPBF zone and the DED zone. Although the phase compositions of both the LPBF zone and the DED zone are composed of alpha-Al matrix and eutectic Si, the melt track shape, microstructural morphology, grain size, grain boundary angle distribution and grain texture change significantly around the LPBF/DED interface. The results of mechanical property tests indicated that the LPBF zone has higher microhardness and tensile strength but lower elongation in comparison with the DED zone. The fine microstructure containing a large number of Si-rich nano-precipitates and high amount of solid solution element enhance the microhardness and tensile strength of the LPBF zone, where the lower solid solubility and high percentage of low angle grain boundary increased the elongation of the DED zone. More importantly, the tensile strength of the LPBF/DED interface is not less than the DED zone, and the boundary of DED melt track as well as porosity defect in the DED zone are the weakest region of LPBF/DED hybrid laser additive manufacturing AlSi10Mg specimens. Therefore, the overall tensile strength of the sample is mainly determined by the DED zone. The formation mechanism of the gradient microstructure around the LPBF/DED interface and the effect of microstructure on properties were also analyzed. This paper proves that the LPBF/DED hybrid laser additive manufacturing technology can be used for the overall manufacturing of aluminum alloy components with regular surface structure.