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The fabrication of multi-layer alloys by additive friction stir deposition (AFSD) results in a complicated microstructure and mechanical property evolution due to the repeated thermal inputs impacting the existing deposited layers. This work systematically studied the microstructure and mechanical properties of several areas (last layers, intermediate layers, and first layers) of a 16-layer 2195 alloy component fabricated by AFSD to ascertain the effect of repeated thermal cycling. The periodic heat input resulted in the minimal quantities of T1-phase only appearing in the last layers of the sample, while the θ′-phase developed a complex precipitate with the δ′ and β′ phases. The mechanical properties of the 2195 sample exhibit a gradient development related to the microstructure, with a decrease in strength and hardness from top to bottom. The samples located in the last layers show the highest microhardness of 117.0 Hv, yield strength of 296.6 MPa, ultimate tensile strength of 440.6 MPa, and elongation of 27.1%, respectively. [ABSTRACT FROM AUTHOR]

Structural repair of high-strength 7075 Al alloys is vital in aerospace and defense field. Nevertheless, conventional melting-based welding methods pose challenges in achieving this due to the generation of solidification defects. In this work, 7075 Al alloy plates were successfully repaired by an emerging solid-state additive manufacturing technology, additive friction stir deposition (AFSD). The effect of different heat treatment states of feedstock rod (T6-treated and solution-treated) on the microstructure and mechanical properties of the repaired zone were systematically investigated. The results show that the repaired zone of the T-repair specimen is partly filled with material flowing from the sidewall of the hole and partly with deposited fine equiaxed grains, showing no distinct interface. In contrast, the repaired zone of the S-repair specimen is completely filled with deposited equiaxed grains. The T-repair showed higher mechanical properties of 312.6 MPa and 9.7%, respectively, compared to 252.1 MPa and 7.9% for the S-repair. To further improve the mechanical properties of T-repair, post-repair heat treatment (PRHT) was performed. After PRHT, the tensile strength of T-H-repair increased to 491 MPa, but elongation decreased significantly. The decreased elongation after PRHT can be ascribed to the aggregation of precipitated phases at the repair interface. [ABSTRACT FROM AUTHOR]

Al-Sn alloy is utilized as a bearing material to replace conventional Sn-based alloy in the design of bearing liners due to its higher load-carrying capacity and wear resistance. However, cracks readily initiate in casting Al-Sn alloy near the coarse Sn phase, leading to low mechanical properties and insufficient wear resistance. The present study introduces a new method, additive friction stir deposition (AFSD), to produce AlSn20Cu alloy with fine grains and sub-micron-scale Sn phases, resulting in enhanced mechanical performance and wear resistance. Compared to both casting and cold rolling + annealing AlSn20Cu alloys, the ultimate tensile strength of AFSD AlSn20Cu alloy is improved by 80.56 % and 16.67 % respectively. Additionally, AFSD AlSn20Cu alloy demonstrates a lower coefficient of friction (COF) and lower wear rate without significant subsurface damage. This is attributed to the fine and uniformly distributed Sn phase forming a uniform and dense surface lubrication layer that adapts the friction pair to the boundary lubrication state, preventing the initiation and development of cracks. • AlSn20Cu alloy was produced by additive friction stir deposition (AFSD). • •The AFSD alloy is characterized by fine grains and sub-micron-scale Sn phases. •The AFSD alloy exhibits outstanding mechanical performance and wear resistance compared to both casting and cold rolling + annealing alloys. •This is attributed to the fine and uniformly distributed Sn phase in AFSD alloy. •The fine Sn phase prevented the initiation and development of cracks. [ABSTRACT FROM AUTHOR]

Additive friction stir deposition (AFSD) provides innovative solutions to circumvent problems related to repairing defects of material by means of solid-state filling. In this work, the cooling conditions during the AFSD on microstructural evolution and mechanical response of repaired Al-Zn-Mg-Cu alloy were investigated for the first time. Repaired Al-Zn-Mg-Cu alloy under air-cooling and water-cooling conditions exhibited distinctive microstructure, i.e., the grain size, dislocation density, and precipitations, as well as resultant mechanical properties, owing to the different thermal features (peak temperature, thermal exposure duration, and cooling rate). Specifically, the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of air-cooling specimens were 262.3 MPa, 370.9 MPa, and 9.8 %, respectively. The YS, UTS, and EL of water-cooling specimens were 302.1 MPa, 421.1 MPa, and 11.3 %, respectively, which were 15.2 %, 13.5 %, and 14.3 % higher than that of air-cooling specimens. For the AFSD repaired Al-Zn-Mg-Cu alloy with water-cooling condition, the enhancement of mechanical properties mostly arises from increased cooling rate and decreased thermal duration compensating for the deterioration of the dislocation density and precipitated phases during the thermal process. • AFSD in repairing Al-Zn-Mg-Cu alloy were investigated. • AFSD was performed under various cooling conditions. • Repaired alloy exhibited different microstructure under various cooling. • Water-cooling sample showed the highest mechanical performance. • This arises from the high cooling rate and shortened thermal duration. [ABSTRACT FROM AUTHOR]