The use of pre-alloyed powders in SAW allows for better control of the required chemistry in coating applications, because the pre-alloyed powder chemistry can be tailored to the required chemistry for the specific application [25]. In addition, the use of pre-alloyed powders to form the cladding alloy, as compared to alloy formation via the weld wire, limits weld metal dilution. Dilution from the iron contained in the weld wire is negated, and dilution from the substrate steel is limited because the weld pool is cooled due to the melting of the added powders. Overall deposition productivity is also improved due to the application of metal powders [25]. In the application of pre-alloyed Ni-containing powders, containing 27-29% Cr, 5-8% Ni, 2-4% Mo in iron alloy matrix, the nickel yield values ranged from 57 to 78% [25]. Although the same patent referred to the application of Co-containing pre-alloyed powders with up to 40% Co, no yield data was mentioned. Because Ni and Co have similar oxygen affinity, melting and boiling points, and vapor pressures vs. temperature, it may be expected that cobalt's yield to the weld metal is similar to that of nickel. However, cobalt yield information seems to be limited or has often been assumed to be 100%. Since cobalt is expensive at $US 27/lb currently, and price increases are expected due to cobalt demand associated with Li-ion battery manufacture for electric cars, it is important to maximise Co yield to the weld metal [26; 27]. Therefore, investigation of cobalt's chemical behaviour in SAW is of importance, irrespective of its application in cladding or joining operations. Although aluminium is not typically added in large quantities to steel, recent developments of low density/high-entropy steels and low density stainless steels require high quantities of aluminium in their formulations [28; 29]. Therefore, it is expected that combinations of alloying elements with aluminium will become increasingly important in expanding the application of SAW to these newer steel grades. Manufacturing weld wires of specific compositions is expensive and time consuming. Furthermore, available weld-wire compositions are limited and cannot match all desired alloy compositions. Closer matched alloying of the weld metal may be better accomplished if metal powder is applied to the welding process to achieve the desired weld metal composition [25]. Pre-alloyed powder manufacturing is also time consuming, and suffers from limits in matching capabilities; a better cost alternative is the application of unconstrained metal powders in SAW. A limited number of published studies are available on the application of unconstrained (not fluxed cored wire or metal cored wire) metal powders for alloying purposes in SAW. In particular, the behaviour of cobalt when used as alloying powder is not clear, although it has been qualitatively reported as equally vapour-forming to nickel in the same welding process [22]. The objective of the current study is to demonstrate the application of unconstrained cobalt and aluminium powders in SAW, to alloy the weld metal and control the weld metal oxygen content. The SAW process chemical interaction of Al and Co metal powders with welding flux has not been specifically discussed in the published literature. Therefore, the secondary objective of this work is to apply thermodynamic analysis to elucidate the chemical behaviour of Co and Al metal powders in the SAW process.