Evolution mechanism of interfacial microstructure in TC4/AlSi10Mg multi-material using CuSn10 interlayer fabricated by laser powder bed fusion

In this study, TC4/AlSi10Mg multi-material was successfully fabricated via laser powder bed fusion using CuSn10 alloy as an interlayer. Effects of CuSn10 interlayer on the microstructure and mechanical property of the multi-material interfaces were systematically investigated. Emphases were placed on analyzing the evolution mechanisms of the TC4/CuSn10 interface and the CuSn10/AlSi10Mg interface under different laser powers, as well as the formation mechanism of gradient equiaxed grains at the TC4/CuSn10 interface. As laser power increases, interfacial width expands. Along the building direction, granular structure (β-Ti + Ti₂Cu), reticular structure (Ti₂Cu + TiCu), feather-like structure (TiCu₂Al + Ti₃Cu₄), and cellular structure (TiCu₂Al + α-Cu) were formed at the TC4/CuSn10 interface. Lack-of-fusion defects were detected at the TC4/CuSn10 interface under lower laser powers, while pores appeared at the interface of samples under higher laser power. Layered Al₄Cu₉ phase, columnar Al₂Cu phase, and cellular α-Al phase were identified at the CuSn10/AlSi10Mg interface. Both lack-of-fusion defects and microcracks can be detected at the CuSn10/AlSi10Mg interface under lower laser power. Tensile test results verified that the bonding strength of the CuSn10/AlSi10Mg interface was inferior to that of the TC4/CuSn10 interface. Under the combined action of gravity-driven convection and Marangoni convection, improved metallurgical bonding of the TC4/CuSn10 interface was achieved. Gradient equiaxed grains emerged at the region near the CuSn10 region within the TC4/CuSn10 interface. TiCu₂Al zone and α-Cu/TiCu₂Al duplex zone were formed sequentially in the region along the building direction. At the bottom of TiCu₂Al zone, inhomogeneous distribution of Al element brought about low nucleation rate, resulting in coarse grains. In the middle of TiCu₂Al zone, the grain refinement was promoted due to large temperature gradient and uniform elemental distribution. At the top of TiCu₂Al zone, uniform elemental distribution gave rise to moderate grain size. In α-Cu/TiCu₂Al duplex zone, Ti-induced constitutional undercooling in the liquid phase, together with the mutual phase pinning between α-Cu and TiCu₂Al, led to the formation of fine equiaxed grains.