Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Metal-based additive manufacturing, or three-dimensional (3D) printing, is a potentially disruptive technology across multiple industries, including the aerospace, biomedical and automotive industries. Building up metal components layer by layer increases design freedom and manufacturing flexibility, thereby enabling complex geometries, increased product customization and shorter time to market, while eliminating traditional economy-of-scale constraints. However, currently only a few alloys, the most relevant being AlSi10Mg, TiAl6V4, CoCr and Inconel 718, can be reliably printed; the vast majority of the more than 5,500 alloys in use today cannot be additively manufactured because the melting and solidification dynamics during the printing process lead to intolerable microstructures with large columnar grains and periodic cracks. Here we demonstrate that these issues can be resolved by introducing nanoparticles of nucleants that control solidification during additive manufacturing. We selected the nucleants on the basis of crystallographic information and assembled them onto 7075 and 6061 series aluminium alloy powders. After functionalization with the nucleants, we found that these high-strength aluminium alloys, which were previously incompatible with additive manufacturing, could be processed successfully using selective laser melting. Crack-free, equiaxed (that is, with grains roughly equal in length, width and height), fine-grained microstructures were achieved, resulting in material strengths comparable to that of wrought material. Our approach to metal-based additive manufacturing is applicable to a wide range of alloys and can be implemented using a range of additive machines. It thus provides a foundation for broad industrial applicability, including where electron-beam melting or directed-energy-deposition techniques are used instead of selective laser melting, and will enable additive manufacturing of other alloy systems, such as non-weldable nickel superalloys and intermetallics. Furthermore, this technology could be used in conventional processing such as in joining, casting and injection moulding, in which solidification cracking and hot tearing are also common issues.

3D printing of high-strength aluminium alloys

3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting

A review of selective laser melting of aluminum alloys: Processing, microstructure, property and developing trends

The interest for a wider range of usable materials for the technology of selective laser melting (SLM) is growing. In this work, the manufacturing of wrought Al–Cu–Mg parts using SLM technology was systematically investigated. The effect of processing parameters on the density of the deposited Al–Cu–Mg samples was studied. It shows that the laser energy density plays a significant role in the densification behavior of the Al–Cu–Mg powder during the SLM process. The laser energy density value of 340 J/mm3 is found to be the threshold, above which high density samples (99.8%) without imperfections and microcracks can be obtained. The SLMed Al–Cu–Mg part presents a unique layer-wise feature which consisted of an extremely fine supersaturated cellular-dendrites structure. The ultimate tensile strength of 402 MPa and the yield strength of 276 MPa are achieved for the SLMed Al–Cu–Mg part. The combination of grain refinement and solid solution strengthening mechanisms during SLM process are proposed to explain the high mechanical strength.

Selective laser melting of high strength Al–Cu–Mg alloys: Processing, microstructure and mechanical properties

Selective laser melting of Al7050 powder: Melting mode transition and comparison of the characteristics between the keyhole and conduction mode

Contact angle evolution during selective laser melting

The proposed paper illustrates the fabrication and heat treatment of high strength Al-Cu-Mg alloy produced by selective laser melting (SLM) process. Al-Cu-Mg alloy is one of the heat treatable aluminum alloys regarded as difficult to fusion weld. SLM is an additive manufacturing technique through which components are built by selectively melting powder layers with a focused laser beam. The process is characterized by short laser-powder interaction times and localized high heat input, which leads to steep thermal gradients, rapid solidification and fast cooling. In this research, 3D Al-Cu-Mg parts with relative high density of 99.8% are produced by SLM from gas atomized powders. Room temperature tensile tests reveal a remarkable mechanical behavior: the samples show yield and tensile strengths of about 276 MPa and 402 MPa, respectively, along with fracture strain of 6%. The effect of solution treatment on microstructure and related tensile properties is examined and the results demonstrate that the mechanical behavior of the SLMed Al-Cu-Mg samples can be greatly enhanced through proper heat treatment. After T4 solution treatment at 540°C, under the effect of precipitation strengthening, the tensile strength and the yield strength increase to 532 MPa and 338 MPa, respectively, and the elongation increases to 13%.

Fabrication and heat treatment of high strength Al-Cu-Mg alloy processed using selective laser melting

It is a crucial issue to eliminate cracks for selective laser melting (SLM) 7xxx series aluminum alloy. This paper aims to study the effect of silicon content on the cracking behavior and the mechanism of eliminating crack of SLMed Al7050 alloy.,Six different silicon contents were added to the Al7050 powder. The crack density and crack count measuring from optical micrographs were utilized to judge the cracking susceptibility. The low melting phases analyzing from Jmatpro and the microstructure observing by EPMA and SEM were used to discuss the mechanism of eliminating the crack.,The cracking susceptibility of SLMed Al7050 alloy decreases with the increase of adding silicon content. When adding silicon, two new low-melting phases appeared: Mg2Si and Al5Cu2Mg8Si6. These low-melting phases offer much liquid feeding along the grain boundary and decrease the cracking susceptibility. Moreover, the grains are obviously refined after adding silicon. The fine grain can increase the total surface area of the grain boundary, which can reinforce the matrix and decrease the cracking susceptibility. High silicon content results in more low-melting phases and fine grains, which decreases the cracking susceptibility.,The investigation results can help to obtain crack-free SLMed Al7050 parts and deep knowledge on eliminating cracking mechanism of high-strength aluminum alloy fabricated by SLM.

Ting Qi

Papers

Selective laser melting of high strength Al–Cu–Mg alloys: Processing, microstructure and mechanical properties

Selective laser melting of Al7050 powder: Melting mode transition and comparison of the characteristics between the keyhole and conduction mode

Contact angle evolution during selective laser melting

Fabrication and heat treatment of high strength Al-Cu-Mg alloy processed using selective laser melting

Effect of Si content on the cracking behavior of selective laser melted Al7050