Selective Laser Melting for Joining Dissimilar Materials: Investigations of Interfacial Characteristics and In Situ Alloying

Abstract

Joining multi-materials with complex geometries is a promising method to achieve multi-functional components that overcome traditional manufacturing limitations. Selective laser melting (SLM), also known as laser powder bed fusion (LPBF), is an additive manufacturing (AM) technique that enables the production of complex geometries, but it typically operates using a single material and a substrate made of the same material. Here, we show that the SLM technique can be used to join dissimilar printed materials (pure Al, pure Cu, and 50 at. pct Al-50 at. pct Cu mixed powders, respectively) with a typical stainless steel (316L) substrate. We investigate the interfacial characteristics between dissimilar materials processed at various laser energy densities and the feasibility of in situ alloying during the SLM process. Moreover, we employ the finite element method (FEM) to visualize the melting behaviors of Al and Cu powders upon laser irradiation. Pure Al and Cu powders join the stainless steel with distinct characteristics through diffusion and melting. We also produce an Al-Cu alloy with uniformly distributed elements by the SLM processing of Al-Cu mixed powders. Our study demonstrates the feasibility of joining dissimilar materials and in situ alloying in the SLM process.

Appendices

Appendices

1.1 Simulation Models & Parameters

During the additive manufacturing process, metals can be melted and subsequently evaporated via the heat transferred from laser to material powders. Laser energy is mainly absorbed by the upper surface in the melting process and then a hole is formed in the powder because of evaporation. To demonstrate the laser energy absorbed by the powder via the upper surface and keyhole, both surface heat source model and body heat source model are defined in the simulation. The surface heat source is supposed to have a Gaussian distribution and the body heat source model can be defined with the heat generation rate per unit volume. The two heat source models can be described as follows[51]:

$$ q_{{{\text{Surface}}\left( {x,y} \right)}} = \frac{{3{\text{Pe}}_{1} }}{{\pi r_{1}^{2} }}e^{{\left( {\frac{{ - 3\left( {x^{2} + y^{2} } \right)}}{{r_{1}^{2} }}} \right)}} $$

(A1)

$$ q_{{{\text{Body}}\left( {x,y,z} \right)}} = \frac{{3{\text{Pe}}_{2} }}{{\pi \left( {1 - e^{ - 3} } \right)hr_{2}^{2} }}e^{{\left( {\frac{{ - 3\left( {x^{2} + y^{2} } \right)}}{{r_{2}^{2} }}} \right)}} $$

(A2)

where P is the laser power, e₁ and e₂ represent the ratio of laser energy absorbed by the upper surface and keyhole, r₁ and r₂ are the radius of the surface heat source and body heat source, and h represents the height of the body heat source.

1.2 Microstructure of the SLM-Processed Al Melt Tracks

See Figure A1.

Fig. A1

SEM micrographs of the (a) needle-like microstructure at the Al-stainless steel interface and (b) dendrites observed in the center of the Al melt track. These images are inserted in Fig. 3

1.3 Transformation from the Columnar to Equiaxed Dendrites

See Figure A2.

Fig. A2

SEM micrographs of the (a, c) Al-Cu melt tracks produced at different laser energy densities (2.3 and 3.8 J/mm, respectively) and (b, d) microstructural evolution from the columnar to equiaxed dendrites