Solid-state cladding on thin automotive sheet metals enabled by additive friction stir deposition

Abstract

• Additive friction stir deposition enables good cladding on 1.4 mm-thin substrates. • The reinforced structure is characterized by good formability and high strength. • The mechanical forces from the tool cause no local buckling in the thin substrates. • The residual stress and mismatch strain are first quantified for this new process. • The maximum tensile stress is around 40 MPa and the mismatch strain is 7.37 × 10 - 4 . Additive friction stir deposition is an innovative solid-state additive manufacturing process that creates near-net-shape 3D components based on deformation bonding rather than melting and solidification. Here, we employ this process for selective cladding on thin Al-Mg-Si sheet metals and evaluate its feasibility for automotive manufacturing based on the cladding quality and substrate distortion. We show that under optimal conditions, additive friction stir deposition can produce high-quality cladding without surface or interface porosity even if the substrate is as thin as 1.4 mm. In addition, the high strength and good formability of the original Al-Mg-Si substrate are preserved in the post-cladding reinforced structure, which exhibits an ultimate tensile strength of 250 MPa and an elongation of 30 %. Despite the mechanical forces imposed by the tool during deposition, no local buckling or wrinkling is observed in the thin substrate. During cooling, however, in situ monitoring shows that mild, global substrate distortion gradually develops. Upon unclamping, the cladding-on-plate system reconfigures itself to minimize the potential energy, leading to an anticlastic curvature. Based on the curvature measurement and classical lamination theory, this work provides the first quantification of the residual stress caused by this newly-developed additive technology, in which the maximum tensile stress is estimated to be around 40 MPa in the rectangular reinforced structure and the interface mismatch strain is 7.37 × 10 −4 . Both values are low thanks to the solid-state nature of the process.