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A continuous net-like eutectic structure enhances the corrosion resistance of Mg alloys
0.2~0.5 mm/year) to match the bone healing process. concentration, and porous around the TiAl particles
3
In the present work, the degradation rate of AZ61 alloy would form, which made the alloys easily to crack in
was dramatically decreased from 0.74 (1.56 mm/year) to the grain boundary, resulting in reduced compressive
0.24 mg·cm /d (0.51 mm/year ) after adding 0.5 wt% strength [36] . The microhardness of AZ61-Ti was
−1
−2
1
Ti. The improved corrosion resistance could be explained increased with the increase of Ti content, which could
from two aspects as follows. On the one hand, Ti be attributed to the fine grain strengthening. Besides,
promoted the formation of divorced eutectic α phase and the eutectic α and β phases had higher microhardness
reduced the formation of divorced β-Mg Al phase. than α-Mg matrix, which could also contribute to the
12
17
Significantly, the potential difference between the eutectic increase of microhardness.
α phase and α-Mg grains was slighter than that between
β-Mg Al phases and α-Mg grains, due to the lower 5. Conclusions
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17
potential of eutectic α phase and a reduced potential In this study, Ti-introduced AZ61 alloy was fabricated
[32]
difference would decrease the susceptibility to galvanic with SLM to enhance the corrosion resistance. Results
corrosion of AZ61-0.5Ti. indicated that Ti promoted the formation of eutectic α-Mg
On the other hand, the continuous net-like eutectic phase and reduced the formation of β-Mg Al phase.
α phase also did a favor for the enhanced corrosion When the Ti content reached to 0.5 wt%, the eutectic α-Mg
17
12
resistance. During degradation, the α-Mg grains phase formed a continuous net-like structure providing
dissolved preferentially, leaving the eutectic α phase on resistance for α-Mg matrix. Polarization test, hydrogen
the surface . Al-enriched eutectic α phase was relatively evolution, pH value, Mg concentration, and mass
[33]
2+
inert in the physiological environment. Thus, the exposed loss suggested that AZ61-0.5Ti exhibited the optimal
eutectic α phase would act as a barrier and retard the corrosion resistance. The typical corrosion morphologies
corrosion to a certain extent. For AZ61 and AZ61-0.25Ti, demonstrated that the AZ61-0.5Ti suffered uniform
the discontinuous eutectic α phase did not form an corrosion. Besides, AZ61-0.5Ti showed improved
effective barrier to corrosion attack, as shown in Figure 2. compressive strength and microhardness compared to
Resultantly, the AZ61-0.5Ti exhibited higher corrosion AZ61 due to solid solution strengthening and fine-grain
resistance compared with AZ61 and AZ61-0.25Ti. strengthening. In addition, the Ti contained Mg alloys
It should be noted that with Ti further increasing to exhibited good cytocompatibility.
1 wt%, the TiAl phase precipitated in grain boundary
3
(Figure 2), which exhibited higher potential difference Acknowledgment
with α-Mg grains than that between the eutectic α phase
and α-Mg grains. Hence, the TiAl phase was considered This study was supported by the following funds: (1) The
3
as the cathode and form galvanic cells with α-Mg grains, natural science foundation of China (81871494, 81871498,
resulting in dramatically galvanic corrosion. Thus, the 51705540); (2) Hunan provincial natural science foundation
galvanic corrosion was considerably enhanced, which of China (2018JJ3671, 2019JJ50588); (3) Guangdong
decreased corrosion resistance of AZ61-1.0Ti. province higher vocational colleges and schools pearl river
scholar funded scheme (2018); (4) The open sharing fund
4.3 Mechanical Properties for the large-scale instruments and equipments of central

Mechanical properties were closely related to South university; (5) The project of hunan provincial science
microstructure. In the present study, AZ61-Ti exhibited and technology plan (2017RS3008); Shenzhen science
equiaxed grains with eutectic α and β phases on the and technology plan project (JCYJ20170817112445033);
interdendritic regions (Figure 2). The formation of the (6) National postdoctoral program for innovative talents
Al-enriched eutectic α phase was a solid solution of Al (BX201700291); (7) The China postdoctoral science
in α-Mg phase, which caused a negative deformation foundation (2018M632983); (8) The fundamental research
of the lattice structure and increased the dislocations funds for the central universities of central South University
resistance that occurred in grains [34,35] . Moreover, the (2019zzts005).
addition of Ti significantly refined the grains, increased References
the grain boundaries, and suppressed the formation of β
phase. Resultantly, the crack tendency and the fracture 1. Staiger M, Pietak A, Huadmai J, et al., 2006, Magnesium and its
propagation were reduced. Thus, the compressive Alloys as Orthopedic Biomaterials: A Review. Biomaterials,
strength of AZ61-Ti was improved. However, as Ti 27:1728-34. DOI 10.1016/j.biomaterials.2005.10.003.
was more than 0.5 wt%, the coarse TiAl particles
3
precipitated and aggregated at the grain boundaries, 2. Zhao D, Witte F, Lu F, et al., 2017, Current Status on
which broke the connection between the adjacent Clinical Applications of Magnesium-based Orthopaedic
grains. As external force was applied to specimen, stress Implants: A Review from Clinical Translational

58 International Journal of Bioprinting (2019)–Volume 5, Issue 2