Page 60 - MSAM-1-4

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

homogenize the microstructure of the SLMed Ti Al V alloy, 3. Performance of LPBF developed Mg alloys
6
4
the results showed that fracture strain increased from 0.21
to 0.65 after FSP. In addition, FSP improves the ductility 3.1. Mechanical properties
and fatigue life of the SLMed-AlSi Mg alloy, due to the An ideal orthopedic implant should have sufficient
10
spheroidization of the eutectic phase, the homogenization mechanical strength and excellent stress conduction
of the microstructure, and the reduction in porosity . capability, matches with the surrounding bone tissue, and
[66]
However, to the best of our knowledge, there are only a provides mechanical support during the healing process
very limited number of studies relating to the adjustment of bone tissue. Processing method directly affects the
of the microstructure and enhanced mechanical properties mechanical properties of Mg alloys. Compared with cast
of SLMed-Mg alloys by FSP. Deng et al. found that FSP Mg alloys, due to the influence of grain refinement, solid
[67]
treatment of SLMed-Mg alloys resulted in a reduction of solution strengthening, and other factors, the mechanical
porosity from 0.779% to 0.015%, disappearance of melt properties of Mg alloys manufactured by laser AM have
pool boundaries, columnar to equiaxed transformation, been improved to varying degrees in various aspects.
and grain refinement, which significantly improved the The mechanical properties of bone are closely related to
mechanical properties of the Mg-Gd-Zr alloy. age, bone health, and bone type. Zhang et al. prepared
[70]
porous Mg scaffolds with porosity of 33 – 54% using fiber
2.3.4. Laser beam polishing deposition hot pressing technology, and their Young’s
Laser polishing is an efficient, non-contact, and fully modulus and compressive strength were comparable to
automated post-treatment technology that provides those of human cancellous bone.
excellent performance in reducing the surface roughness Hyer et al. used LPBF to prepare a dense WE43 alloy.
[71]
of SLMed parts. In the past two decades, laser polishing Under the compressive action, the average yield strength
has been widely used to reduce the surface roughness of the newly built WE43 structure was 224 MPa, the
of polymers, metals, ceramics, and other materials. compressive strength was 417 MPa, and the failure strain
In contrast to conventional polishing processes, laser was 9.5%. Under tension, the newly constructed LPBF
polishing smoothens rough surfaces using thermal energy WE43 has an average yield strength of 215 MPa, a tensile
to melt a thin layer of material, as shown in Figure 9. In strength of 251 MPa, and a failure strain of 2.6%. A study
laser polishing, a precisely controlled laser beam is guided by Fang et al. on the mechanical properties of hot rolled
[72]
onto the surface of the part for polishing. By controlling and WAAM-GTA prepared AZ31 samples showed that the
the energy of the laser beam, the peak on the surface is just performance of WAAM-GTA AZ31 along the direction of
melted, and the molten metal is generated due to the multi- travel was always better than that along the build direction.
directional surface tension and gravity, and then, it is filled Whether there were large pores within the specification
into the valley. In this case, there is no material loss during length of the processed tensile samples, its mechanical
laser polishing. The laser power, spot size, and scanning properties will vary. Deng et al. systematically analyzed
[53]
speed are the main control parameters to obtain a smooth the effect of different solution conditions and aging heat
surface . At present, laser polishing has demonstrated its treatment on the microstructure and mechanical properties
[68]
ability to polish various materials, from reflective materials of SLM GZ112K alloy. Appropriate post-heat treatment
such as aluminum to high strength materials such as Inconel is an effective measure to improve the microstructure
and titanium alloys . Unfortunately, there are no relevant and mechanical properties of SLMed alloy. SLM-T6 alloy
[69]
reports on laser polishing for SLMed Mg alloys. meets the requirements of high tensile strength, SLM-T4
alloy meets the requirements of high ductility, and SLMed
alloy achieves a good combination of tensile strength and
ductility. The ultra-high yield strength of SLM-T6 GZ112K
alloy mainly comes from the following four aspects: Fine-
grain strengthening with average grain size <3.1 μm,
precipitation strengthening of β΄-aging precipitation,
secondary phase strengthening of long-period stacking-
ordered (LPSO) structure and X phase, and the extra
composite strengthening from the coexistence of basal
[73]
and prismatic precipitates. Wang et al. studied the
effect of geometric design on the dynamic response
of additively fabricated Mg scaffolds, and the results
Figure 9. Schematic diagram of laser beam polishing. showed that geometric design had a significant effect on

Volume 1 Issue 4 (2022) 9 https://doi.org/10.18063/msam.v1i4.24