# Effect of ElectroSpark Process Parameters on the WE43 Magnesium Alloy Deposition Quality
## 1 Introduction  
Over the last few decades, aerospace and aeronautical industries have shown a strong interest for the coating/repair procedures of high-valued parts through the use of safe, reliable, economic and environmentally friendly innovative technologies [1; 2]. The majority of the conventional deposition processes (such as HVOF, PVD, CVD, electro plating and etc.,) used to improve components' wear and corrosion resistance are characterized by high costs equipment, length processing, and pollution [3; 4; 5]. Furthermore, these techniques are not suitable to coat or repair the heat sensitive alloys widely used in aerospace applications (i.e., aluminum and magnesium alloy) due to the high thermal input involved that induces a large heat affected zone (HAZ), residual stresses and distortions [1; 4; 5; 6; 7; 8; 9]. These effects deserve attention because typically they degrade the mechanical performances. The aeronautical industries commonly employ light materials such as aluminum and magnesium alloys for producing components [10]. Particularly, the WE43 alloy, belonging to the magnesium-rare earth-zirconium (Mg-RE-Zr) system, is the most used between existing magnesium alloys because of its high specific strength, good castability and machinability, high thermal conductivity, high dimensional stability, good electromagnetic shielding property together with improved mechanical properties up to 250 \({}^{\circ}\)C. At the same time, this alloy is characterized by low creep resistance and poorstability of the properties when exposed at temperatures above 300 \({}^{\circ}\)C. The WE43 alloy is often used for helicopter transmissions, power systems, aero engines, gearbox casings, missiles, and sport cars engine blocks [11; 12; 13; 14]. That alloy is usually processed by casting and exhibits various defects like shrinkage porosity and cracks [11; 12; 13; 14]. Due to the cracks susceptibility of WE43 alloy, the conventional high heat input deposition techniques are not suitable for the repair of the WE43 components [15; 16; 17]. In this context, ElectroSpark Deposition (ESD) technology appears as a very interesting solution to apply coatings to improve corrosion and wear-resistance and for the restoration of damaged high valued parts particularly for those materials ordinarily considered un-weldable by conventional weld processes [2; 18; 19; 20; 21]. In fact, ESD is a type of low heat-input pulsed micro-bonding process where a consumable material electrode is deposited onto a conductive component's surface through a series of high-energy density electrical pulses of short duration, typically ranging from a few microseconds to milliseconds. In the ESD process, the electric arc generated between the electrode tip and the substrate is able to melt a small material volume fraction of both the substrate and the electrode. Specifically, the small molten droplets from the electrode are propelled and accelerated by the electric field towards the substrate where they crash. The single drop of electrode material that impinges on the substrate is identified with the term \"splat\", while the resulting morphology of the deposit surface is therefore defined as \"a splash\". During the advancement of the electrode, the drops are deposited in sequence on the substrate generating thin layers of material. In ESD process the bonds between the adjacent splats or splat/substrate develop by both melting and diffusion [22; 23; 24; 25; 26]. The many benefits of ESD include a low-pollution, the technological simplicity of metal deposition at atmospheric pressure, the portability of the equipment for use in shop or in field and the low cost of the machine. Moreover, being a low heat input process, usually ESD does not induce distorsions or microstructural changes in heat sensitive substrate and is applicable to those materials possessing a high tendency to cracks during welding such as superalloys, McArIY and thermally sensitive materials [24; 25; 26; 27; 28].