A novel incremental forming method coupled with additive manufacturing for heterogeneous Steel/Al laminated structures

Abstract

Laminated sheet metal parts comprise two or more substrate sheet metals to leverage the respective performance advantages, yielding superior overall performance with wider application prospects compared to single-layer parts. However, traditional manufacturing methods for sequentially bonding and forming extend development cycle time with poor part performance. In the present work, a novel hybrid manufacturing method synchronizing incremental sheet forming with friction stir additive manufacturing for laminated sheet metal parts is proposed. Through experiments, microstructural characterization and mechanical testing, the influence of process parameters on the mechanical properties and microstructure of heterogeneous materials are investigated. Inspired by biological structure, multiple heterogeneous structures are introduced to enhance the mechanical properties and bonding performance, including dual-gradient grain and bimodal grain structures in material matrix and interlocking corrugated texture at the Steel/Al interface. The dual-gradient grain structure from surface to interior of steel matrix reflects a transition from grain refinement to dynamic recrystallisation. The coarse grains in bimodal structure of aluminum matrix underwent severe plastic deformation with significant precipitation behavior and the ultrafine grains exhibit recrystallisation behavior along with numerous stacking faults. It is also found that the average misorientation value in the corrugated interface is markedly higher than those in material matrix, along with abundant dislocations and twin structures within interfacial compound layer. Both yield strength and shearing strength of laminated sheet materials significantly increase with rising pre-strain and interface corrugation, reaching 437 MPa and 112 MPa at a pre-strain of 0.30 and corrugated amplitude of 10 μm, respectively and encompassing those of laminated materials by conventional processes reported. This work reveals a fundamental mechanism that heterostructure-induced stress partitioning contributes to the synergistic enhancement of mechanical property and interfacial bonding, with the contribution rate of back stress reaching 76% of yield stress. Finally, case studies demonstrate the proposed process realizes integrated forming-bonding-additive manufacturing of laminated sheet metal parts with short cycle time, enabling the in-situ engineering of multi-scale heterogeneous structures to simultaneously improve strength and bonding performances.