In the aircraft industry, the high-strength aluminum alloys AA7075 and AA2024 are extensively used for the manufacture of structural parts like stringers and skins, respectively. Additive manufacturing (AM) of the AA7075-T6 aluminum alloy via friction stir deposition to build continuously multilayered parts on a substrate of AA2024-T4 aluminum has not been attempted so far. Accordingly, the present work aimed to explore the applicability of building multilayers of AA7075-T6 alloy on a substrate sheet of AA2024-T4 alloy via the additive friction stir deposition (AFSD) technique and to optimize the deposition process parameters. The experiments were conducted over a wide range of feed rates (1–5 mm/min) and rotation speeds (200–1000 rpm). The axial deposition force and the thermal cycle were recorded. The heat input to achieve the AFSD was calculated. The AA7075 AFSD products were evaluated visually on the macroscale. The microstructures were also investigated utilizing an optical microscope and scanning electron microscope (SEM) equipped with an advanced EDS technique. As well as the presence phases, the mechanical performance of the deposited materials in terms of hardness and compressive strength was also examined. The results showed that the efficiency of the deposition process was closely related to the amount of heat generated, which was governed by the feeding rate, the rotational speed, and the downward force. AA7075 defect-free continuously multilayered parts were produced without any discontinuity defects at the interface with the substrate at deposition conditions of 1, 2, 3, and 4 mm/min and a constant 400 rpm consumable rod rotation speed (CRRS). The additively deposited AA7075-T6 layers exhibited a refined grain structure and uniformly distributed fragment precipitates compared to the base material (BM). The gain size decreased from 25 µm ± 4 for the AA7075-T6 BM to 1.75 µm ± 0.41 and 3.75 µm ± 0.78 for the AFSD materials fabricated at 1 and 4 mm/min deposition feeding rates, respectively, at 400 rpm/min. Among the feeding rates used, the 3 mm/min and 400 rpm rod rotation speed produced an AA7075 deposited part possessing the highest average hardness of 165 HV ± 5 and a compressive strength of 1320 MPa.

Two B400B-R and B500B grade rebars were industrially produced through a Tempcore process. The standard chemical composition of B500B grade was additionally alloyed with 0.067 wt.% V to enhance its mechanical properties. A set of optimized processing parameters were applied to manufacture two different diameters D20 (Ø 20 mm) and D32 (Ø 32 mm). The microstructure -mechanical properties relationships were evaluated using optical and scanning electron microscopes, hardness, and tensile testing. In addition, a thermal model was developed to define the thermal cycle evolution during cooling in the quenching & tempering box (QTB) to simulate the kinetics of V(C,N) precipitation. The microstructure observations showed a typical graded microstructure consisting of ferrite-pearlite core and outer tempered martensite ring for both grades of both diameters. The optimized processing parameters for B400B-R of D32 (compared with D20) resulted in softening of the core (from 160 to 135 HV10) and tempered martensite surface (from 220 to 200 HV10) as well as in decreasing the yield strength (from 455 to 413 MPa) and tensile strength (from 580 to 559 MPa). On the contrary, an increase in hardness of the core (from 165 to 175 HV10) and the outer tempered martensite (from 240 to 270 HV10), in addition to an increase in yield strength (from 510 to 537 MPa) at almost the same level of tensile strength of 624–626 MPa are observed for B500B grade D32 compared with D20. The modeling and simulation calculations suggest that the manufacturing D32 rebars of B500B grade involves longer quenching time in the QTB which allow deeper tempered martensite surface along with a relatively higher core temperature that renders faster kinetics and larger volume fraction of V(C,N) precipitates. The current study demonstrates that the full potential of V-alloying can be exploited when a sufficient quenching time at the equalization temperature is achieved, which is valid for D32 rebars.