Influence of Compositionally Graded Interface on Microstructure and Compressive Deformation of 316L Stainless Steel to Al12Si Aluminum Alloy Bimetallic Structures

Bimetallic structures offer properties that can be customized based on applications, manufactured in one operation. Such manufacturing options are fascinating, as joining two metallic materials, especially for two dissimilar metals without significant defects, is challenging. In this study, 316L stainless steel (SS) to Al12Si aluminum alloy structures were processed, tailoring the compositionally graded interface on a SS 316 substrate using a directed energy deposition (DED)-based additive manufacturing (AM) process. Applying such a compositionally graded transition for joining two dissimilar metals could mitigate the mismatch of mechanical and thermal properties. This study's objective was to understand the processing parameters that influence the properties of AM processed SS 316L to Al12Si bimetallic structures. Two different approaches were used to fabricate these bimetallic structures. The results showed no visible defects on the as-fabricated samples using four layers of Al-rich mixed composition as the transition section. The microstructural characterization showed a unique morphology in each section. The microstructural variation was caused due to various processing parameters such as laser power, powder feed rate, and laser scan speed. FeAl, Fe2Al5, and FeAl3 intermetallic phases were formed at the compositionally graded transition section. After stress relief heat treatment of the bimetallic samples, diffused intermetallic phases were seen at the compositionally graded transition. At the interface, as processed bimetallic structures had a microhardness value of 834.2 ± 107.1 HV0.1, which was a result of the FeAl3 phase at the compositionally graded transition area. After heat treatment, the microhardness value reduced to 578.7 ± 154.1 HV0.1 because of a more Fe-dominated FexAly phase formation. Compression test results showed that the non-HT and HT SS 316L/Al12Si bimetallic structures had a similar maximum compressive strength of 299.4 ± 22.1 MPa and 270.1 ± 27.1 MPa, respectively. These results demonstrated that the applied heat treatment conditions only had a minor impact on samples' compression strength.