**4. Metals and alloys for Wire Arc Additive Manufacturing**

WAAM processes exactly use available electrode wires of materials that are produced by the welding industries and readily available in the spooled form in alloys as feedstock to welding processes. The materials to choose for WAAM process are completely based on the application requirements. For example, some materials may be preferred by automotive industries, aerospace industries, and so on [5, 13]. To cover these application requirements, the following familiar metals are available for WAAM.


WAAM community suggests that the Nickel-based alloys as the most popular materials for the fabrication by welding process due to their weld ability and high strength at elevated temperatures. Nickel-based alloys are widely used in aerospace, petrochemical, chemical, and marine industries due to their exceptional strength and oxidation resistance at high-temperature ranges. In WAAM, alloys such as Inconel 718 and Inconel 625 have been proved to be feasible alloys so far for WAAM processing. Fabrication trials for many different series of aluminum alloys have been carried out already using Al-Cu (2xxx), Al-Si (4xxx), Al-Mg (5xxx) and also using many alloys. The WAAM is mainly a justifiable process for structures as the cost of manufacturing the small and simple aluminum alloy component by conventional machining processes is comparatively less. Though many of the Al alloys such as Al 7xxx and 6xxx are still challenging to weld for WAAM fabrication due to the reason of turbulent melt pool and defects, the rigorous activities are being undertaken regarding aluminum alloys because of the superior benefit that additively manufactured aluminum alloy parts have inferior mechanical properties compared to those machined from billet material. In order to achieve higher tensile strength, most of the as-deposited aluminum parts undergo post-process heat treatment to refine the microstructure. Compared to other alloys these alloys are cheaper and easily available, the WAAM of these components gaining enormous interest irrespective of fabrication complexity.

Additions of chromium to iron and aluminum as an alloying element have been to improve the anti-corrosion properties of the structure and could be a potential candidate for increasing the lifetimes of the various corrosive environment applications. Titanium alloys contain a mixture of pure titanium and other chemical elements and these alloys have high tensile strength and toughness at the wide range of temperatures. They are generally lighter in weight and pose superior anticorrosion properties. However, the high cost and processing limitations make these alloys to use in superior areas such as military and aerospace applications, sports, and bio-medical industries. WAAM is highly attempted for the fabrication for these areas with cost benefits. Stainless steel originally referred to as rustless steel, is a group of ferrous alloys that contain a minimum of approximately 11% chromium, this has made stainless steel as rust-free together with heat-resistant properties. Different types of stainless steel generally include the elements such as carbon, aluminum, silicon, nitrogen, sulfur, nickel, titanium, copper, selenium, niobium, and molybdenum. Sensitization is a major problem in austenitic type of stainless steels comparing ferritic steels and martensitic steels. Apart from this, residual stress, metallurgical properties, weld distortion and thermal properties of the WAAM manufactured components are to be taken with much care for the successful lifetime of components. Other metals such as magnesium, bronze, and many more intermetallic structures could be possible with this WAAM process but care must be given to improve the properties of such fabricated structure components.
