Page 442 - IJB-10-4

International Journal of Bioprinting Improving ductility of 3D-printed Zn–Mg

Mg alloys (Table 2). The Mg concentration within the α-Zn indicated that increasing the Mg concentration would
matrix for Zn–1Mg, Zn–3Mg, and Zn–5Mg was 0.74, reduce the corrosion rate of Zn–Mg alloys.
1.15, and 3.20 wt%, respectively. With an increase in Mg The morphologies of the surfaces of the LPBF-fabricated
concentration, the concentration of dissolved Mg within Zn–1Mg, Zn–3Mg, and Zn–5Mg alloys (immersed in the
the α-Zn matrix also increases. Furthermore, a comparison SBF solution for 14 days) are presented in Figure 8a, e,
between the Mg concentration at grain boundaries and and i, respectively. Generally, no visible cracks or pores
within the matrix for the same compositions demonstrated were observed on the surfaces of LPBF-fabricated Zn–
the enrichment of Mg at the grain boundaries of the α-Zn Mg samples, indicating minimal corrosion. The standard
matrix. The polyhedral structure exhibited by the black potential of Zn–Mg intermetallic compounds is similar
grains (observed in the SEM images) suggests that they to pure Zn, 26,39 indicating negligible galvanic corrosion.
corresponded to the MgZn phase. After 14 days, the three alloys exhibited uniformly
2
3.3. Degradation characteristics of fabricated distributed white spherical corrosive products (~1 μm).
Zn–Mg alloys Among them, the surface of Zn–1Mg displayed the most
The LPBF-fabricated Zn–Mg alloys, which exhibited the extensive corrosive product coverage (60–70% of the total
highest relative density, were assessed for their degradation visual field area), with some aggregation and small cracks
properties. Figure 7 depicts the in vitro immersion appearing in the precipitates. The surface of Zn–3Mg
corrosion behaviors of the fabricated Zn–Mg alloys with displayed slightly fewer corrosive products compared to
varying Mg concentrations. The pH variation curves of the Zn–1Mg; however, there was a slight product aggregation
SBF solution after immersing the Zn–Mg alloys for 28 days without observable cracks in the precipitates. In contrast,
are depicted in Figure 7a. The pH values of the three alloys only scattered corrosion products were observed on the
rapidly increased within the initial 10 days of immersion, surface of Zn–5Mg.
reaching a relatively stable state at day 14. The increase in The morphologies of the fabricated Zn–1Mg, Zn–3Mg,
pH can primarily be ascribed to the release of OH ions and Zn–3Mg alloy surfaces after 28 days of immersion are
−
during the immersion process: 38 depicted in Figure 8b, f, and j, respectively. A significant
increase in both the quantity and size of corrosive products
M + 2H O → M + H + 2OH − (2) on the surfaces of the three alloys was observed, with
2+
2
2
complete coverage of the visual field area. Specifically, the
where M represents Zn or Mg. Among them, the size of the corrosive products on the Zn–1Mg surface grew
fabricated Zn–1Mg alloy exhibited a slightly higher pH to approximately 2 μm, accompanied by wider cracks within
compared to that of the Zn–3Mg and Zn–5Mg alloys, the precipitates that spanned across the entire surface.
suggesting a higher corrosion rate for Zn–1Mg than Medium-sized areas displayed detachment within these
for Zn–3Mg and Zn–5Mg. Figure 7b presents the ion precipitates. The Zn–1Mg matrix exhibited a smooth and
concentrations of the alloys after immersing the alloys flat surface, indicating the prevention of further corrosion
for 28 days in the SBF solution. The concentration of Zn within the film. An enhanced aggregation of corrosive
2+
40
remained consistent across all three alloys at approximately products with dispersed tiny cracks was observed on the
30 mg/L. Conversely, the concentration of Mg decreased surface of Zn–3Mg. Although noticeable growth and
2+
from 89.72 to 38.01 mg/L as the Mg concentration ranged aggregation occurred on the surface of Zn–5Mg, it was lower
from 1 to 5 wt%. Figure 7c illustrates the corrosion rates compared to that observed for Zn–1Mg. Throughout the
of Zn–1Mg, Zn–3Mg, and Zn–5Mg alloys during the entire immersion testing, Zn–1Mg exhibited a significantly
immersion corrosion process, which are calculated to be higher abundance of surface corrosive products compared
0.126, 0.113, and 0.090 mm/year, respectively. These results to Zn–3Mg and Zn–5Mg. Moreover, Zn–1Mg displayed an
accelerated corrosion rate, resulting in the generation of a
greater quantity of corrosive products within the same time
frame. EDS analysis performed on the corrosive products
Table 2. Mg concentration (wt%) of laser powder bed fusion from the Zn–Mg alloys indicated the presence of Zn, Ca, P,
(LPBF)-fabricated Zn–Mg alloys measured through energy- Cl, and O. The predominant constituents identified for the
dispersive X-ray spectroscopy (EDS)
corrosive products in a chloride solution were zinc oxide,
Position Mg concentration (wt%) zinc hydroxycarbonate, and zinc hydroxyphosphate. 34,41
Zn–1Mg Zn–3Mg Zn–5Mg The corrosion resistance of LPBF-fabricated Zn–Mg
Grain 0.78 ± 0.05 1.15 ± 0.09 3.20 ± 0.09 alloy improved with increasing Mg concentration, and
Grain boundary 1.74 ± 0.12 4.74 ± 0.22 5.45 ± 0.89 this could be attributed to the formation of a Mg-rich

Volume 10 Issue 4 (2024) 434 doi: 10.36922/ijb.3034