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Here, we present the first demonstration of additive friction stir deposition of Ti-6Al-4V with closed-loop temperature control, wherein the print head rotation rate is adjusted in real-time to maintain a constant tool temperature during deposition. The as-printed Ti-6Al-4V is fully dense, achieving forging standard tensile properties along both the in-plane and out-of-plane directions. The measured yield strength, ultimate tensile strength, and elongation are 903 MPa, 1000 MPa, and 17% along the in-plane direction, and 948 MPa, 1024 MPa, and 16% along the out-of-plane direction. With closed-loop temperature control, the microstructure is found to be comparable along the thickness direction, contrasting the previous work performed under parameter-controlled conditions. For all the deposition conditions explored in this work, the deposited Ti-6Al-4V exhibits a lamellar microstructure with alpha laths forming inside prior beta grains, indicating higher peak temperatures than the beta transus. The increase of a pseudo heat index leads to an increase in the prior beta grain size and a decrease of the out-of-plane yield strength. Deposition of Ti-6Al-4V is seen to modify the microstructure of the substrate near the interface: the original equiaxed microstructure is replaced by lamellar and bimodal microstructures. We finally discuss the possibility of forming equiaxed microstructures in the as-deposited Ti-6Al-4V and provide evidence for different types of microstructures forming in the same deposition layer, which may be caused by the thermal gradient during reheating. [ABSTRACT FROM AUTHOR]

Owing to the occurrence of hot cracking during solidification and vaporization of solute elements during melting, beam-based additive manufacturing has encountered serious problems in printing high-strength, nonweldable Al alloys. After aging, the mechanical properties of these alloys are often substantially inferior to their wrought alloy counterparts. Here, a deformation-based additive process is used for printing high-strength 7075 Al alloy (i.e., AA7075), wherein frictional heating is leveraged to enable rapid plastic deformation. The as-printed material consists of a refined, equiaxed microstructure and shows no surface or interface porosity. After proper solution treatment and aging, the yield strength, ultimate tensile strength, and elongation of the printed AA7075 are measured as 477 MPa, 541 MPa, and 8.2%, respectively. These values are a notable improvement from those published for beam-based additive manufacturing and are comparable to the typical properties of wrought alloy AA7075. With a comparison to the feed material, these values account for 95% of the yield strength, 94% of the ultimate tensile strength, and 78% of the elongation of the wrought AA7075-T6 with the exact same composition. Additional printing and testing show that wrought-like mechanical properties can be consistently achieved using this approach without adding new elements or nanoparticles. Unlabelled Image • Non-weldable 7075 Al is additively manufactured by deformation-based additive manufacturing without hot cracking or porosity. • Wrought-like mechanical properties, including strength and ductility, are achieved in the printed 7075 Al. • Fine, equiaxed microstructures are achieved in the as-printed state without the addition of new elements or nanoparticles. [ABSTRACT FROM AUTHOR]

• 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. [ABSTRACT FROM AUTHOR]