## 3 Results and Discussion
### Analysis of Mechanical Properties  
The mechanical properties of both electrolytic and hot-dip zinc coatings were evaluated using the Erichsen cupping test, which was conducted prior to corrosion testing (Figure 15). This sequence was chosen to prevent voluminous corrosion products from hindering the objective assessment of the zinc-coated samples after salt spray exposure [18]. The cupping test measures the ability of both the coating and substrate to undergo plastic deformation. The later the sample fails, the greater the plasticity of the coating or substrate. During testing, the sample is clamped between a holder and a punch, where a spherical-ended punch (20 mm diameter) indents the surface until a visible crack appears.  
For electrolytically deposited zinc, the lowest elasticity was observed in samples with steel grit-blasted substrates. This effect is attributed to the high hardness of the subsurface layers, which increases brittleness in the affected steel region. Although pure zinc is a ductile metal, the 350 \(\upmu\)m-thick hardened steel layer significantly exceeds the thickness of the zinc coating [37]. As a result, cracks in the zinc coating formed network-like patterns, similar to those observed in hot-dip zinc coatings. Quantitatively, this similarity was evident as cracks appeared at an indentation depth of approximately 2 mm in both cases, indicating very low ductility [50]. Among electrolytically deposited zinc coatings, the highest ductility was observed in the reference sample, which correlated with the lowest subsurface hardness. The ground surface exhibited similar substrate hardness, though its surface microgeometry contributed to a minor statistical reduction in elasticity. For hot-dip zinc coatings, the low ductility is primarily due to the inherent brittleness of intermetallic compounds and the relatively high coating thickness. However, hot-dip zinc coatings without intermetallic phases can be achieved through continuous galvanizing using the Sendzimir method, which is known to improve coating elasticity. The main drawback of this method is the reduced zinc coating thickness, which is comparable to electrolytic zinc deposition [2; 20; 37; 44]. As shown in previous studies [51; 52; 53], the cupping test is widely used for objective assessment of coating ductility. Due to the greater elasticity of electrolytic zinc coatings, imaging required a microscope with a greater depth of field.  
Figure 15: Results of the Erichsen cupping test (arithmetic mean \(\pm\) standard deviation; immersion time for electrolytic zinc coating: 4500 s, hot-dip zinc coating: 210 s).  
Consequently, images were captured using a digital microscope (Figure 16). In contrast, for hot-dip galvanized samples, a metallographic microscope was sufficient for imaging (Figure 17).  
Figure 16: Appearance of samples with electrolytic zinc coating (immersion time: 4500 s) after the cupping test: (**a**) blasted with synthetic corundum (4.2 mm), (**b**) blasted with steel grit (2.3 mm), (**c**) ground (5.8 mm), and (**d**) reference sample (6.1 mm).  
Figure 17: Appearance of samples with hot-dip zinc coating (immersion time: 210 s) after the cupping test: (**a**) blasted with synthetic corundum (1.9 mm), (**b**) blasted with steel grit (2.1 mm), (**c**) ground (1.9 mm), and (**d**) reference sample (2.3 mm).