A perspective on precipitation-hardening high-entropy alloys fabricated by additive manufacturing

Wire arc additive manufacturing (WAAM) is suitable for printing medium-to-large complex parts with structural integrity while reducing material wastage, and lead time, improving the quality and customized design for functional components. Aluminium alloys are one of the most commonly used metallic materials in manufacturing parts for aerospace and automotive applications due to their lightweight, excellent strength, and corrosion resistance properties. Aluminium alloys have been employed in the WAAM process to produce parts for the aerospace and automotive industries. In this paper, various research works associated with the application of WAAM of aluminium alloys for aerospace and automotive industries, their metallurgical characteristics, and mechanical properties have been reviewed and discussed in detail to identify the research gap and future research directions. This paper is patterned to provide a comprehensive review of WAAM of aluminium alloys for the production of parts in the aerospace and automotive industries. Abbreviations: AM: Additive manufacturing; Al: Aluminium; Bi: Bismuth; BIW: Body in white; CNC: Computer numerical machines; CMT: Cold metal transfer; CNN: Convolutional neural networks; CL: Curved layer; DE-GMAAM: Double-electrode gas metal arc additive manufacturing; DWAAM: Double wire arc additive manufacturing; DMD: Direct metal deposition; DMLS: Direct metal laser sintering; DED-arc: Directed energy deposition arc; 3D: Three-dimensional; EAC: Environmentally assisted cracking; EBM: Electron beam melting; FCI: Fatigue crack initiation; Fe: Iron; GTAW: Gas tungsten arc welding; GMAW: Gas metal arc welding; HE: Hydrogen embrittlement; HAZ: Heat-affected zone; HWAAM: Hot wire arc additive manufacturing; IISCC: Irradiation induced stress corrosion cracking; Li: Lithium; Mg: Magnesium; Mn: Manganese; Ni: Nickel; OL: Online cooling; Pb: Lead; PAW: Plasma arc welding; RS: Robotic system; SCC: Stress corrosion cracking; SLM: Selective laser melting; SCG: Short crack growth; SLC: Super light car; Si: Silicon; Ti: Titanium; Zr: Zirconium

Wire arc additive manufacturing of aluminium alloys for aerospace and automotive applications: a review

To meet the urgent demand of large-scale parts fabrication in aerospace and energy fields, laser powder bed fusion (LPBF) additive manufacturing is developing towards multi-laser powder bed fusion (ML-PBF). However, defects such as the surface quality degradation and lack of fusion are more prone to appear at the overlap region of the deposit printed by multiple laser beams, which is detrimental to the consistency and uniformity of parts formed using ML-PBF. Here, based on a high-speed, high-resolution imaging technology and our ML-PBF equipment, the dual-beam laser-matter interaction at the overlap region in ML-PBF was investigated. At the overlap region, the collision and interaction between two molten pools influences the flow pattern of the liquid metal, accompanied by the large-sized droplet spatter expelling out. Moreover, the collision and accumulation of the liquid metal and spatter are responsible for the formation of the surface and internal structure defects of overlap samples. Furthermore, we reveal multiple transitions of the dominant mechanisms of the spatter formation in ML-PBF, which can be interchanged from the vapor-induced recoil pressure dominant stage to the vapor-induced entrainment dominant stage. We also propose the growth rate of spatter number rs, which can be well correlated with the transient transition of spatter formation mechanism. This work is expected to provide the scientific basis for ML-PBF to achieve consistency and uniformity.

Dual-beam laser-matter interaction at overlap region during multi-laser powder bed fusion manufacturing

The rapid development of additive manufacturing requires a large number of printable metallic materials for various engineering applications. In this work, the printability of a high strength aluminum alloy AA2024 was evaluated for laser powder bed fusion (LPBF) with comparisons to the widely used AlSi10Mg. Strikingly different solidification cracking networks were generated when using diverse scanning strategies and overlap rates of adjacent tracks. Depending on the overlap rates, the crack propagation patterns transited from the longitudinal-dominant to the transverse-dominant. The lengths and propagation angles of the transverse zigzag cracks were strongly interdependent and both increased with the overlap rate of adjacent tracks. The characterization results implied that these diverse crack propagation patterns originated from the columnar grain structure, which were produced in the localized solidification conditions determined by the track-wisely moving molten pool. The characteristics of the thermal cycles and solidification conditions of AlSi10Mg and AA2024 were further examined using a comprehensive phenomenological model for a better understanding of the printability of AA2024. The results showed that AA2024 generated smaller molten pool and that AA2024 was more susceptible to lack of fusion defects given the same LPBF process conditions. Supported by the evaluated printability of AA2024, a comprehensive scheme targeting the printing of crack-free LPBF builds was proposed considering the heat input, the overlap rate, and the scanning strategies of the laser beam.

Printability assessment with porosity and solidification cracking susceptibilities for a high strength aluminum alloy during laser powder bed fusion

http://manuscript.elsevier.com/S0924013622001091/pdf/S0924013622001091.pdf

F.Q. Liu

Papers

Spatiotemporal variations of residual stresses during multi-track and multi-layer deposition for laser powder bed fusion of Ti-6Al-4V