Fabrication of a 2-layer laminated steel composite by friction stir additive manufacturing

Laminated composites are a kind of material composed of different material layers that are broadly used in various industries. In the present research, the friction stir welding was employed to fabricate a 2-layer composite consisting of interstitial free steel sheets and St52 steel plates. The microstructure and mechanical properties of composites were examined and compared with as-received steel. The results showed that the layers had good bonding and an interface was sharp in the lower travel speed; however, the diffusion takes place in the interface with increasing a traverse speed. The carbon diffusion and formation of a Widmanstatten ferrite in the stir zone and near to two steel interfaces resulted in the highest hardness in the composite cross-section. Unexpected stretched grains formed at the traverse speed of 40 mm/min under the influence of material flow created by the tool shoulder from advancing to retreating side in the stir zone. The bimodal structure formation in the interstitial free steel layer of composite resulted in work hardening rate variation during tensile test. The tensile test and scanning electron microscopy images taken from fracture surface of samples demonstrated that the fragmentation in the interstitial free steel layer followed by dispersed delamination and then St52 failure is dominant scenario in the failure of 2-layer laminated steel composite made in this study.