A laser powder bed fusion (LPBF) Inconel 718 (IN718) alloy was fabricated under different process parameters, and the samples with optimal process parameters were treated by subsequent heat treatment. The outcomes demonstrated that the pores’ size and shape were influenced by the process parameters. The porosity of the samples first grew and subsequently reduced as the volume energy density increased, and the types of pores changed from lack-of-fusion pores to gas holes and keyhole pores. The porosity of the samples with three process parameters were 3.46%, 0.15% and 1.26%, respectively. The sample of 60.0 J/mm³ was chosen for a single solution (heat treatment at 980 °C for 1 h, SS) and direct aging (heat treatment at 720 °C for 8 h and then 620 °C for 8 h, DA), and the microstructure evolution of the samples was examined. Because of the segregation of the elements Nb and Mo, the Laves phase was distributed among the dendrites in the as-built (AB) sample. The solution heat treatment dissolved the Laves phase and precipitated the δ phase, while aging heat treatment precipitated the γ′/γ” phases. Additionally, the impact of the second phase on the tensile characteristics was looked into. The DA sample had the highest strength, with a tensile strength of 1458 MPa and a yield strength of 1271 MPa. With tensile and yield strengths of 980 MPa and 620 MPa, respectively, the AB sample had the lowest strength due to the Laves phase’s role as the crack initiator. The Laves phase dissolved and the γ′/γ”-strengthened phase precipitated, leading to an increase in the strength of the heat-treated specimens.

High-efficiency and high-quality welding has always been the focus of welding research. This article proposes a novel double-pulse, triple-wire MIG welding process for the welding of 6082-T6 aluminum alloy. The process characteristics of welding arc and droplet transfer were studied, and the performances of weld formation, morphology, hardness, and tensile strength were tested for the 1 Hz, 3 Hz, and 5 Hz double-pulse welding and normal-pulse welding. It was found that in the welding process, the pulsed arc steadily alternated among three welding wires without arc interruption, and the arc length changed periodically with the double-pulse frequency. The droplets transferred with a stable one-pulse-one-drop mode. Besides, a proper double-pulse frequency, e.g., 3 Hz in this case, was conducive to forming good welds with regular fish-scale patterns and no pores. The tensile strength of the joint could reach 64% of the base material’s tensile strength, and its fracture belonged to plastic fracture, which occurred in the HAZ. This new welding method will have great potential in aluminum alloy welding.

Single-pass keyhole TIG welding (K-TIG) was used to weld 10-mm-thick Invar36 alloy plates without filler metal and groove preparation. The effects of joint gap, welding current, welding speed and arc length on the weld appearance, microstructure and mechanical properties were investigated. No phase transformation occurred in the weld where only austenite (γ-(Fe, Ni)) was formed, while the grain structure changed significantly. The maximum tensile strength of K-TIG weld was 440.7 MPa reaching 99.9% of the base metal and the maximum elongation was 31.5%. The microhardness in the weld zone was slightly lower than that of the base metal. The results suggested that K-TIG welding was a very promising method for the joining of middle-thick Invar36 alloy plates.

The Invar alloy is widely used for aircraft wing mould manufacturing. In this work, keyhole-tungsten inert gas (K-TIG) butt welding was used to join 10 mm thick Invar 36 alloy plates. The effect of heat input on the microstructure, morphology and mechanical properties was studied by using scanning electron microscopy, high energy synchrotron X-ray diffraction, microhardness mapping, tensile and impact testing. It was shown that regardless of the selected heat input, the material was solely composed of austenite, although the grain size changed significantly. The change in heat input also led to texture changes in the fusion zone, as qualitatively determined with synchrotron radiation. With increases in heat input, the impact properties of the welded joints decreased. The coefficient of thermal expansion of the joints was measured, which demonstrated that the current process is suitable for aerospace applications.