Page 61 - MSAM-1-4

Materials Science in Additive Manufacturing LPBF of Mg and its bio-applications

the compression fatigue performance of Mg scaffolds. and thus increases their degradation rate. In this case,
A summary of the mechanical properties of the additively the corrosion resistance of Mg alloys can be significantly
manufactured biodegradable Mg alloys from the literature improved by adopting high purification methods or
is presented in Table 3. reducing the impurity concentration by improving
the processing technology. Han et al. found that the
[80]
3.2. Degradation performance degradation rate of high purity Mg in vivo was much lower
The previous studies have shown that AM prepared Mg than that of Mg-containing iron impurities. Cao et al.
[81]
and its alloys possess fine grain size and homogeneous slowed down the corrosion rate of Mg alloys by adding a
microstructure, which can obtain lower degradation rates, certain amount of Zr to the molten Mg alloy to remove
mainly due to improved passivation properties and reduced the impurity iron. Studies have shown that Zr and iron
micro-galvanic corrosion . Despite that, their corrosion can easily form a precipitate phase, which precipitate at
[77]
rate in the body fluid environment is still unable to meet the the bottom of the melt, thereby achieving purification
[82]
needs of bone implants. For an ideal biodegradable bone effect. Peng et al. used a zone solidification method to
metal implant, they have a corrosion rate of <0.5 mm/year prepare Mg alloys and found that the corrosion rate of
and need to provide mechanical support for 12 – 24 weeks the alloys purified by this method was lower than that of
to meet the clinical requirements [78,79] . This means that the conventionally cast Mg alloys.
AM-processed biodegradable Mg and its alloys implants
need to be regulated. The corrosion resistance of the 3.2.2. Alloying treatment
additively manufactured Mg and its alloys in the current Alloying treatment is an effective way to improve the
studies is summarized in Table 4. corrosion resistance of Mg alloys by changing the
microstructure and the type of precipitates. At present,
3.2.1. Scavenging effect researchers have developed a series of biological Mg
Many impurities, such as iron, nickel, and copper, in Mg alloys by alloying methods, and their properties have been
and its alloy commonly exhibit relatively high potential. studied. Shuai et al. found that with the increase of Al
[83]
This causes the micro-galvanic corrosion with matrix content, α-Mg dendrites and intermetallic compounds

Table 3. Mechanical performances of the LPBF‑manufactured biodegradable Mg alloys

Type Mechanical properties Improvement mechanisms
Shapes Materials Dimensions
Block ZK60 [41] Cubic Microhardness: 89.2 Hv High densification, fine-grain
6 × 6 × 6 mm 3 strengthening, and solution
strengthening
AZ91D [46] Bone-shaped gauge UTS: 296 MPa, Fine-grain strengthening
25 × 6 × 2 mm 3 UYS: 254 MPa
Microhardness: 100 HV
AZ61 [49] Bone-shaped gauge UTS: 287.1 MPa, Fine-grain and solid solution
25 × 6 × 1.5 mm 3 UYS: 233.4 MPa, strengthening
EL: 3.12%
GWZ1031K [53] Bone-shaped gauge UTS: 347 MPa Fine-grain strengthening
18 × 3 × 10 mm 3 UYS: 310 MPa
EL: 4.1%
Mg-8Zn [74] Cuboid Hardness: 71.5 Hv Fine-grain strengthening
5 × 5 × 3 mm 3
Porous Mg-Ca [50] Cuboid UCS: 111.19 MPa Optimizing the laser parameters
6 × 6 × 9 mm 3 Elastic modulus: 1.26 GPa
ZK61 [52] Cuboid Microhardness: 106.75 Hv Fine-grain strengthening, solution
6 × 6 × 9 mm 3 UCS: 50.95 MPa strengthening, and precipitation
Elastic modulus: 0.91 GPa strengthening
WE43 [75] Cylindrical Hardness: 77.41 Hv Optimized structure of porous units
D (6 mm), UCS: 21.21 MPa
H (6 mm) Elastic modulus: 0.79 GPa
WE43 [76] Cubic fluorite UCS: 71.48 MPa Optimized structure of porous units

Volume 1 Issue 4 (2022) 10 https://doi.org/10.18063/msam.v1i4.24