Page 58 - MSAM-1-4

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

Table 2. Additive manufacturing process parameters for magnesium and its alloy
Material Laser power (W) Laser spot size (μm) Scanning speed (mm/s) Layer thickness (μm) Hatch spacing (μm)
Mg [47] 100 50 10 100 /
Mg-xZn [48] 70 50 100 100–200 /
AZ61 [49] 150 70 400 40 60
AZ91D [46] 200 / 500 40 90
ZK30 [48] 75 150 15 50 50
ZK60 [41] 50 150 8 100 100
ZK60-xCu [48] 60 150 10 / 100
Mg-Ca [50] 80 10 / 40 150
ZK60-BG [51] 80 140 / 60 60
ZK61 [52] 100 / 100 40 1500
WE43 [45] 280 1200 / 30 40
GWZ1031K [53] 80 200 / 30 100

2.3. Post treatments thereby obtaining almost fully dense parts, as shown in
Figure 6. Gangireddy et al. showed that at higher initial
[57]
SLM, as a typical AM technology, can reliably prepare
Mg-based products, which especially own complex porosity, HIP treatment was beneficial for the densification
geometries and do not require molds and accessories . of LPBF formed WE43 magnesium alloys, but could not
[54]
Besides, it also possesses these advantages, such as small improve the densification of samples with smaller porosity
machining allowances and high material utilization. Notably, due to the closed nature of the pores. The cooling rate of
Mg is susceptible to oxidation due to its high chemical laser AM is much higher than that of traditional casting,
reactivity and relatively low melting and boiling points to and an excessively fast cooling rate may be detrimental to
cause high evaporation during melting [55,56] . Therefore, SLM- the precipitation of strengthening phases. A large amount
processed Mg alloy parts exhibit many defects such as high of residual stress caused by excessive cooling rate, texture,
surface roughness, porosity, residual stresses, anisotropy, and and mechanical anisotropy generated along the direction of
[58]
undesired microstructures, which can greatly reduce the heat flow can be eliminated by heat treatment .
overall performance of the parts. The removal of the defects 2.3.2. Calcium hydrogen phosphate dihydrate (DCPD)
is of great practical importance, where some post-treatments
are commonly performed, especially hot isostatic pressing The surface roughness of as-built parts affects the mechanical
(HIP) and calcium hydrogen phosphate dihydrate (DCPD). properties and degradation rate. Coatings can modulate
the degradation behavior and improve the biological
2.3.1. Hot isostatic pressing (HIP) properties. Wang et al. applied DCPD to the surface
[59]
HIP is a frequently used thermomechanical treatment coating of JDBM porous scaffolds with helical tetrahedral
method that eliminates the porosity and relieves the residual structural units, as shown in Figure 7. DCPD treatment
stresses, thus improving ductility, fatigue resistance, and slowed down the degradation rate of the scaffolds and
[60]
microstructure. The method is performed under high- improved their biocompatibility. Dou et al. used the sol-
temperature and -pressure conditions, in which the gel impregnation method to prepare 45S bioactive ceramic
temperature and pressure usually reach 1000 – 2000°C and coatings on AZ31 Mg alloy substrates and found that the
200 MPa, respectively. The working pressure generated by a corrosion resistance was significantly improved. Rojaee
[61]
high-pressure inert gas in a closed vessel is close to the yield et al. synthesized hydroxyapatite coating on AZ91 alloy
point of the as-built parts, thus causing plastic deformation. by electrophoretic deposition process, which significantly
The parts are pressed evenly in all directions with high improved its corrosion resistance and biological properties.
[62]
temperature and pressure, which eliminates these defects to Razavi et al. prepared nanostructured magnesite and
form a dense and uniform microstructure. Therefore, the diopside coatings by electrophoretic deposition, which
treated parts can show high density, good uniformity, and also improved the corrosion resistance and biological
excellent performance. Esmaily et al. processed WE43 activity of magnesium alloys. Kopp et al. used plasma
[63]
[45]
Mg alloy through SLM and found that HIP treatment is electrolytic oxidation (PEO) to treat the surfaces of WE43
an effective method to eliminate the processing defects, Mg alloy scaffolds with different pore sizes prepared by

Volume 1 Issue 4 (2022) 7 https://doi.org/10.18063/msam.v1i4.24