# Study of the Direct Metal Deposition of AA2024 by ElectroSpark for Coating and Reparation Scopes
## 2 Experimental Setup  
The substrate and electrode material is an AA2024-T4 alloy, based on Al-Cu-Mg system. The suffix (T4) indicates that the alloy has been naturally aged (at Room Temperature) after solutionizing. The substrate was supplied as rolled plates 4 mm thick: 80 \(\times\) 20 mm strips were cut from the plates. The deposit was deposited up on the strip, performing multiple depositions on the same line along the rolling direction (RD). The scheme of the depositions is shown in Figure 1.  
The chemical composition (wt %) of 2024 alloy is listed in Table 1.  
Figure 1: Scheme of ElectroSpark Deposition (ESD) process. ElectroSpark Deposition was performed using a \"Technocoat MicroDepo Model 150\" ESD machine (TechnoCoat International, Shizuokaken, Japan). The deposition was carried out at room temperature using a hand-held gun with Ar protection. The Argon was flowed throughout the deposition process at a rate of 10 L/min. Before performing the deposit process, the substrate was polished with 800-grit SiC paper. The rotational speed of the 3 mm diameter electrode was kept constant at 1200 rpm throughout the trials, whereas the other three parameters voltage, capacitance, and frequency, were properly varied. To determine the feasibility of producing thick deposits using the ESD process, for each set of parameters, multiple-layer depositions were performed using 50 subsequent deposition passes. The spark pulse-energy (\(E\)s) in joule (J) of each set parameter given in the Table 2 was determined as follows:  
\[Es=\frac{1}{2}CV^{2}\]  
where \(C\) is the capacitance in Farad (F) and \(V\) is the voltage in Volt (V); while F is the discharge frequency in Hertz (Hz) [26]. In Table 2 are shown the values of the spark pulse Energies used for processing the samples whereas increasing values of the V, C, and F subscript indicate increasing values of the respective parameters. After the deposition, the deposits were sectioned using a diamond blade on the Short Transverse-Long Transverse, ST-LT, (see Figure 1). The ST-LT sections of the deposits were cold mounted. Then, they were ground and mechanically polished. After that, the specimens were etched using Keller reagent (1 mL HF, 1.5 mL HCl, 2.5 mL HNO\({}_{3}\), and 95 mL H\({}_{2}\)O). The analysis of the microstructure was performed by conventional analytical techniques, such as Optical Microscope (OM) Nikon Epiphot 200 (Nikon Inc., Melville, NY, USA) accompanied by a computer-assisted image analysis (NIS Elements AR) and Scanning Electron Microscope (SEM) Zeiss EVO (Zeiss, Jena, Germany) equipped with energy dispersive spectrometry (EDS) technique using a Brucker electron microprobe. The grain structure of BM was revealed, after standard metallographic procedures, through anodizing by Barker's electrolyte at room temperature with 20 V for 50 s. Both of the voids areas inside the deposit and the length of the cracks at the substrate/deposit interface on ST-LT plane (Figure 1) were obtained for each deposit using NIS software for imaging analysis. Especially, defects percentage were measured as the sum of the defects areas divided by the area of the deposit. The average length of the interface cracks was estimated. Vickers micro-hardness (0.05 kg/15 s) was measured in the deposit cross-section (ST-LT plane). Micro-hardness indentations were arranged parallel to the deposit/substrate interface. Three lines of indentations 100 \(\upmu\)m far each other and from interface were realized. Both the average hardness, resulting from the measurements along each line, and the average hardness considering all the indentation made, was calculated. Moreover, the micro-hardness was measured also in some areas of the deposits showing interesting microstructural features.