Advancements in the Additive Manufacturing of Magnesium and Aluminum Alloys through Laser-Based Approach

Abstract

Complex structures can now be manufactured easily utilizing AM technologies to meet the pre-requisite objectives such as reduced part numbers, greater functionality, and lightweight, among others. Polymers, metals, and ceramics are the few materials that can be used in AM technology, but metallic materials (Magnesium and Aluminum) are attracting more attention from the research and industrial point of view. Understanding the role processing parameters of laser-based additive manufacturing is critical to maximize the usage of material in forming the product geometry. LPBF (Laser powder-based fusion) method is regarded as a potent and effective additive manufacturing technique for creating intricate 3D forms/parts with high levels of precision and reproducibility together with acceptable metallurgical characteristics. While dealing with LBPF, some degree of porosity is acceptable because it is unavoidable; hot ripping and cracking must be avoided, though. The necessary manufacturing of pre-alloyed powder and ductility remains to be the primary concern while dealing with a laser-based additive manufacturing approach. The presence of the Al-Si eutectic phase in AlSi10Mg and AlSi12 alloy attributing to excellent castability and low shrinkage, attaining the most attention in the laser-based approach. Related studies with these alloys along with precipitation hardening and heat treatment processing were discussed. The Pure Mg, Mg-Al alloy, Mg-RE alloy, and Mg-Zn alloy along with the mechanical characteristics, electrochemical durability, and biocompatibility of Mg-based material have been elaborated in the work-study. The review article also summarizes the processing parameters of the additive manufacturing powder-based approach relating to different Mg-based alloys. For future aspects, the optimization of processing parameters, composition of the alloy, and quality of powder material used will significantly improve the ductility of additively manufactured Mg alloy by the LPBF approach. Other than that, the recycling of Mg-alloy powder hasn't been investigated yet. Meanwhile, the post-processing approach, including a homogeneous coating on the porous scaffolds, will mark the suitability in terms of future advancements in Mg and Al-based alloys.

Keywords: aluminum; laser-based powder fusion; magnesium; mechanical characteristics; post-processing approach; processing parameters.

Figure 1

Laser powder-bed fusion (LPBF) created an Mg-shaped lattice structure in a magnesium alloy [27].

Figure 2

Advancement in the development of the Mg-based alloy via additive manufacturing powder-based approach [33].

Figure 3

(A) Processing parameters of laser-based powder approach, (B) (a–c) depicted EBSD orientation, (b–d) SEM characterization of AZ91 alloy formed by laser powder bed fusion [27].

Figure 4

EBSD image shows equiaxed, fine, and random grain representation in (a) bulk LPBF-WE43, (b) last melt pool corresponds to basal- orientated, large, and irregular shape grains, (c) basal- orientated, large, irregular shape grains in the bulk sample, (d,e) EDS image at different magnification for same materials, and (f) XRD image depicted intermetallic and oxygen-rich elements in WE43 alloy [27,33,56].

Figure 5

(a) Tensile characterization of additively manufactured Mg-based material via LPBF approach against wrought and cast alloys, (b,c) Fractured surface of (b) Mg-9Al alloy and (c) WE43 alloy [27,54,46].

Figure 6

Major classification of Al alloy, highlighting the key properties and application [145].

Figure 7

Nano-hardness image of an AlSi10Mg alloy fabricated on cast AlSi12 substrate depicted the homogeneity in the SLM material vs the non-uniform profile in the related part; Comparison in the nano-hardness of (a,c) the as-built material, and (b,d) the heat-treated material [161].

Figure 8

Variation in micro-hardness of Al-based materials formed by SLM approach under as-built and heat-treated condition.

Figure 9

Variation in the microstructure of AlSi10Mg alloy relating the micro-hardness depending on the heat treatment process [171].

Figure 10

(a,b) Variation in the Tensile strength vs elongation (%) for Al-based material formed by SLM approach in as-built and heat-treated condition [145].

Figure 11

Tensile fracture of AlSi10Mg alloy formed by SLM approach oriented cross-sectionally comparing (a) as-built sample in the horizontal direction with EDS mapping (c), the heat-treated specimen (b,d). The fracture surface of an as-SLM specimen is oriented in the horizontal direction [161].

Figure 12

(a) fatigue characteristics for AlSi10Mg alloy formed by SLM approach, (b) S-N curves for AlSi12 alloy formed by SLM approach revealing the effect of build plate heating, where batch B does not involve build plate temperature while batch D involved build plate temperature of 200 °C, (c) S-N curves revealed shot peening of AlSi10Mg alloy sample, (d) S-N curves AlSi10Mg alloy revealed variation in fatigue characteristics corresponds to the machining of material and heat treatment [190,191,192].

Figure 13

Backscattered electron images for oxide particles at the boundary between defect area and crack propagation region. An overview at lower magnification is given in (a,c,e), and detailed surface morphology in (b,d,f). Typical EDX spectra at right show the presence of Al and Mg in oxide particles [193].

Figure 14

(a) Influence of heat treatment process on the hardness and wear of AlSi12 alloy formed by SLM approach, (b) tribological behavior of the materials formed by SLM approach comparable to cast counterpart [145].

Figure 15

SEM image depicted AlSi10Mg microstructure formed by (a) SLM, and (b) casting. The arrows in (b) point to (A) Al-Si eutectic, (B) Si dispersed in Al matrix, and (C) Fe-containing intermetallic phases [191].

Figure 16

The microstructure of SLM AlSi10Mg is shown in isometric views in the following order: (a) as-built, (b) after heat treatment; (c,d) elongated α-Al and equiaxed α-Al grains as seen on the XY plane in the as-built material and (e) Si spheroids in the α -Al matrix after T6 heat treatment [192].

Figure 17

The (a) EBSD image depicts the AlSi10Mg alloy grain structure obtained by SLM with columnar cells developing perpendicular to the build direction, (b,c) SEM images show the microstructure in the dashed region and the grain structure using a secondary electron detector, and a backscatter electron detector, respectively. As-built SLM AlSi10Mg cells’ STEM images and associated Al-Si EDX maps are displayed in (d,e) [207].

Figure 18

(a–l) Inverse pole figure orientation map displaying the elongated grain structure’s predominately {1 0 0} orientation along the build direction. Additionally, the orientation map reveals a finer grain structure at the melt’s sides and top, but there is no clear dominating orientation [208,211].

Figure 19

(a) DSC thermogram of an LPBF AlSi10Mg alloy, (b,c) SEM micrographs of as-built and solution-treated and quenched LPBF AlSi10Mg alloy where arrow represents that After solution treatment, it is possible to see how the eutectic network vanishes and how Si particles become more coarse), and (d–g) Mechanical characteristics of solution treated AlSi10Mg alloy [236].

Figure 20

(a–f) Mapping distribution of grain orientation, (g) grain size, and (h) grain aspect ratio of SLM Al–Mn-Sc alloys [252].