Advancements in microwave welding: Susceptor-assisted microwave hybrid-heating technique for metals and polymers

Advancements in microwave welding have made the joining of inherent low dielectric loss materials like metallic (microwave reflectors) and polymeric/thermoplastic (transparent) materials possible. The recent innovative microwave heating, otherwise referred to as the susceptor-assisted microwave hybrid-heating technique (MHHT), has provided a leeway for the welding of these difficult-to-weld materials. Benefits like energy efficiency, cost saving, and uniform/volumetric heating in an eco-friendly style, among others are provided by this new method. Thus, this paper offers an appraisal of microwave heating mechanisms and materials interaction. Overviews on susceptor types as well as the types of interface/filler powders utilized for welding are reported. It also covers susceptor-assisted microwave hybrid heating and welding of stainless steels, mild steels, cast iron, Ni-based superalloys (Inconel and Hastelloy), and thermoplastics. The use of interface Ni-based powders or matching powders with the base alloy to create sufficient wettability and elemental diffusions is central to the success of this welding process. At the moment, MHHT welding is effective in producing completely fused, homogeneous, metallurgical bonded, and crack-free weld structures. Inevitable precipitated intermetallic compounds and carbides are prominent in steel and Ni-based superalloy welds while hard oxides are formed in dissimilar Al/Mg joints. Achieving precise control of the complex microwave heating process remains one of the major challenges of microwave welding. Meanwhile, forward-moving researches are still required on process optimization, machine learning developments, and cutting-edge monitoring technologies in advancing microwave welding science. Other insights into future research areas on microwave-material processing and MHHT are highlighted in this paper.