Microstructure and properties of in situ Al2O3 particle-reinforced aluminium alloy lattice rods fabricated by wire-arc-directed energy deposition

Abstract

Lattice structures have great potential for application in the thermal protection systems of high-performance hypersonic vehicles (Mach > 5). They are lightweight, highly load-bearing and provide good heat insulation. Wire-arc directed energy deposition (WA-DED) is an effective method for preparing lattice structures made from metal lattice rods. A method is proposed to improve the ultimate tensile and compressive strengths of aluminium (Al) alloy lattice rods and lattice structures made by WA-DED. The replacement reaction of Al and NiO generates Al2O3, which was used to improve an Al–Cu alloy (2xxx series). An Al–Cu–NiO system cored wire filled with NiO particles was developed as the raw material for studying WA-DED lattice rods. Then the rod was heat treatment. Tests show that the strength of in situ Al2O3-particle-reinforced Al alloy rods was 281MPa, which is 13.9% higher than that of Al–Cu 2319 Al alloy deposited rods. Reinforcement also increased the elongation (EL) from 11.3% to 13.5%. Strength is increased by Al and NiO reacting in situ to form an Al2O3 phase with refined grains. Most of the generated Ni is dissolved in Al2Cu to form a nano γ-Al7Cu4Ni phase, which plays a second-phase strengthening role. After T6 heat treatment, the strength and EL of 2319-NiO-cored wire deposited rods was 441MPa and 10.4%. Fine, needle-like θ’-Al2Cu structures and Al2O3 and γ-Al7Cu4Ni nanoparticles pin dislocations, prevent their movement and improve the mechanical properties of the rod. The compressive strength of a planar lattice structure after T6 heat treatment was 105MPa and its weight was only 15g, demonstrating high specific strength. Finally, arc additive manufacturing with the developed 2319-NiO-cored wire was used to fabricate a curved-generatrix-shell pyramid lattice structure for use in the thermal protection cone of a hypersonic vehicle. Its thermal insulation coefficient was 82.5%, demonstrating excellent insulation performance. This study provides insights into the manufacturing of thermal protection systems for lightweight, high-strength and high-heat hypersonic vehicles.