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Xie, et al.
A B C

D E

Figure 1. Optical microstructures of SLMed ZK30-0.2Cu-xMn. (A) x = 0, (B) x = 0.4, (C) x = 0.8, (D) x = 1.2, (E) x = 1.6.

The incorporation of Mn into ZK30-Cu by SLM
further increased the hardness. The hardness increased
with the Mn content to a maximum hardness of 117
± 4 HV for the Mn content of 1.6 wt%. This hardness
increase is attributed to grain refinement, solid solution
strengthening, and second-phase strengthening due to
the Mn incorporation. This indeed verifies that Mn is
an effective reinforcement for Mg alloys and hardening
is attained through the incorporation of Mn into the Mg
alloy through SLM.
3.3. Biodegradation
Figure 5 shows potentiodynamic polarization curves for
SLMed ZK30-0.2Cu-xMn tested at 37 ± 0.5°C in the
SBF solution. The incorporation of Mn into ZK30-0.2Cu
by SLM resulted in a change in the corrosion potential
(E ) and the corrosion current density (i ). The E
corr
corr
corr
Figure 2. X-ray diffraction spectra of SLMed ZK30-0.2Cu-xMn. increased with Mn content, which was attributed to the
more positive electrochemical potential of Mn, compared
to Mg. The i values were derived from the linear part
3 (spheroidal precipitate scattered along grain boundaries of the cathodic branch of the polarization potential
corr
and inside the grains) was composed of Mg and Mn. curves using Tafel extrapolation. The incorporation
There was good agreement between the composition of Mn into ZK30-0.2Cu by SLM first decreased the
results determined respectively by EDS spectra and XRD i values. The i values of SLMed ZK30-0.2Cu
patterns. This indicates the presence of MgZn , MgZnCu, and SLMed ZK30-0.2Cu-0.4Mn were 29 μA/cm and
corr
corr
2
2
and α-Mn phases in SLMed ZK30-0.2Cu-1.6Mn. 18 μA/cm , respectively. The i had the minimum
2
corr
2
3.2. Hardness value of 12 μA/cm , while Mn content was 0.8 wt.%.
Thereafter, with Mn content increased to 1.2 wt% and
Figure 4 presents the Vickers hardness values measured 1.6 wt%, the i increased to 32 μA/cm and 40 μA/cm ,
2
2
corr
on the polished surface of the SLMed ZK30-0.2Cu-xMn. respectively, and was even higher than that for the
The hardness of the SLMed ZK30-0.2Cu was 92 ± 3 SLMed ZK 30-0.2Cu without Mn. Using Equation 1, the
HV, while a typical hardness of cast Mg alloys is ~70 biodegradation rates were calculated from the i values
corr
HV . This indicates that SLM significantly enhances the and are presented in Table 3.
[28]
hardness of the Mg alloys which is attributed to the grain Figure 6 shows hydrogen evolution data (Figure 6A)
refinement introduced by rapid solidification during the and weight loss data (Figure 6B) of the SLMed specimens
SLM process. immersed in SBF for 168 h (i.e., 7 days). All the SLMed
International Journal of Bioprinting (2021)–Volume 7, Issue 1 81