Page 74 - MSAM-3-4

Materials Science in Additive Manufacturing Impact resistance and porous structures

high-strength structures in nature. Therefore, it is of great TPMS structures, researchers have attempted various
significance to study the design methods of non-linear optimization schemes, such as twin boundary, hybrid
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gradient structures, especially the relationship between the TPMS innovative design, multi-phase material filling,
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non-linear characteristics of different structural systems and functional gradient design. 26,27 Functional gradient
and their dynamic mechanical properties. 5,6 design is an effective way to improve the performance of
The laser powder bed fusion (LPBF) process is an the TPMS structure. Many biological structures in nature
additive manufacturing (AM) technology that uses a are characterized by functional gradients, for example, the
laser as an energy source to melt metal powder layer by gradient of calcification from inside to outside of the leg
layer. By adjusting the process parameters and scanning bone structure, and the discontinuous gradient of insect
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strategy of the laser, porous aluminum alloy structures carapace cuticle along the thickness direction. Therefore,
with high surface quality and molding accuracy can be researchers combined the functional gradient design
obtained. Aluminum alloy is one of the most widely strategy with structural equivalent density and geometric
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used metal materials, with outstanding strength-to-weight parameters to implement the design. For example, Zhao
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ratios, corrosion resistance, and thermal and electrical et al. explored the compressive properties of gyroid and
conductivity. Previously, aluminum alloy-engineered primitive TPMS structures with functional gradients,
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parts were manufactured using traditional processes, and the results indicated that the EA properties of the
such as casting, powder metallurgy, and forging. These functional gradient structures were significantly improved
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conventional processes usually impose significant compared to the homogeneous structures. The same
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limitations on aspects such as design freedom and conclusion was obtained in the study by Yu et al. Zhang
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complexity of aluminum-alloy structures. Moreover, the et al. investigated the energy storage properties of TPMS
coarse grain structure of aluminum-alloy parts produced structures and found that the energy storage capacity
by conventional processes can also lead to poor mechanical of linear gradient TPMS structures is 1.6 times higher
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properties. To overcome these issues, LPBF provides an than that of uniform structures. Li et al. compared the
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ideal manufacturing process for porous aluminum alloy compression performance of six gradient TPMS structures
structures. Aluminum-silicon alloys are widely adopted and found that smaller cell-sized structures have better EA.
due to alloy compositions that provide a good balance The porosity gradient of the TPMS porous structure
between mechanical properties, weldability, corrosion follows the porosity control function in the implicit
resistance, and castability. 13,14 Among them, AlSi7Mg, as equation. If this function is linear, the TPMS structure
one of the typical aluminum-silicon alloys, provides an exhibits a linear porosity gradient; if it is nonlinear, such
excellent combination of ductility, strength, and corrosion as a cosine function, the porosity changes in a cyclic cosine
resistance for engine parts, hydraulic components, and pattern. Although some literature has explored nonlinear
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non-structural aerospace parts. Recent developments porous structure design methods, research on the effects
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have reported an increase in researching the process ability of periodicity and amplitude oscillations in non-linear
of AlSi7Mg alloys through AM technologies, specifically functional structures on structural changes and properties
the LPBF process. It presents three steps in the development remains limited. The mechanical properties of the
of process parameters for the LPBF-AM of aluminum porous structure are mainly related to the porosity, pore
alloy AlSi7Mg. Moreover, the relationship between distribution, and the type of porous structure. By adjusting
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microstructure and mechanical properties of LPBF- structural design parameters, the non-linear gradient
formed AlSi7Mg has been further investigated. Among of porosity distribution can be regulated to optimize the
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them, surface anomalies and volumetric defects have a mechanical properties, either locally or overall.
greater influence on the fatigue properties of LPBF-formed Therefore, TPMS structures have the potential for use
AlSi7Mg alloys. Magnetic field assistance and subsequent in energy-absorbing applications due to their high specific
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heat treatment can also improve the mechanical properties strength, stiffness, and elastic modulus. 34-36 In this study,
of LPBF-formed AlSi7Mg alloys. 19-21 gyroid, a type of TPMS structure, was selected as the subject
In porous structures, triply periodic minimal surface of study for its self-supporting nature, high flexibility, and
(TPMS) porous structures have the advantages of a smooth EA efficiency. 37-39 This work proposes a design method for
transition, high specific surface area, and good internal non-linear gradient gyroid structures, where the spatial
interoperability. Furthermore, the TPMS structure can distribution of structural porosity is regulated by a nonlinear
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be accurately expressed by mathematical functions, and function. Based on the non-linear gyroid structural design,
the design indexes (e.g., wall thickness, pore diameter, the effect of impact velocity on the dynamic mechanical
and porosity) can be precisely controlled by specific properties of the structure was investigated using a drop-
parameters. To regulate the mechanical properties of hammer impact test, and changes in the 3D morphology
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Volume 3 Issue 4 (2024) 2 doi: 10.36922/msam.5729