New Aluminum Alloy Development Methodology for SLM Under Development

Authors Qingboa Jia, Paul Rometsch, Sheng Cao, Kai Zhang, and Xinhua Wung explain that SLM 3D printing users need some better choices for metals in their recently published, ‘Towards a high strength aluminum alloy development methodology for selective laser melting.’ Because of a limited selection materials, the researchers do not see SLM 3D printing living up to its true potential—especially for use in serious applications such as the automotive industry, aerospace, marine, medical and engineering.

Lightweight aluminum alloys are becoming more popular and are very ‘adaptable’ to SLM 3D printing. These types of alloys are still too limited, however, and the researchers point out that results in 3D printing are often mediocre—leading them to the option of creating a high-performance Al alloy.

Sc (scandium) is a metal element that can be used to strengthen a variety of different alloys—even in just small additions.

“During the SLM process, the solidification rate within molten pools measuring several hundred microns in size can go up to 104–106K/s, which provides the possibility of trapping significantly more Sc into solid solution. After a subsequent ageing treatment, the decomposition of the super saturated Sc in the Al matrix into a correspondingly large volume fraction of nano-sized Al3Sc precipitates provides great potential for precipitation hardening.

The researchers created an easy method to mimic the SLM printing process and predict alloy properties. A wedge mold casting and laser re-melting methodology were used to imitate the SLM solidification process. After that, the researchers were able to create Al-Mn-Sc alloy—both assessed and verified in SLM 3D printing. The ternary Al-Sc-Zr alloy demonstrated a usage hardening response, along with excellent thermal stability. Mn was also chosen as another element to add to the properties of the of the Al-Sc-Zr.

Ageing curves at 300 °C for laser remelted Al-Sc-Zr and Al-7Si alloys. The inset pictures show typical microhardness indentation sizes of samples aged for 168 h. Error bars that arenot showing up are typically within ±0.5 HV0.5

“The SLM-fabricated Al-Mn-Sc alloy demonstrated good laser processability with an absence of solidification cracks and obvious metallurgical defects. Due to the formation of primary Al3(Sc,Zr) particles at the molten pool boundaries, the SLM fabricated Al-Mn-Sc alloy possessed a fine columnar-equiaxed bimodal grain structure.

“A TEM study confirmed the precipitation of a large volume fraction of nanosized Al3Sc precipitates after a simple and industrially desirable direct post-ageing treatment of 5 h at 300 °C. The direct aged Al-Mn-Sc alloy achieved very high yield strength of 570 MPa together with an elongation to fracture of 18%.”

Direct ageing treatment, and lack of fluctuation during the straining process could be a result of homogeneous distribution of precipitates along dislocation slip planes. The study shows that solutes like Mn, massive precipitation of nano-sizeed Al3Sc, and ‘fine-grained’ structures allowed for ‘outstanding qualities.’

While this work sheds light on new and improved alloys for SLM 3D printing, other materials have been created too such as high entropy alloys, titanium mixtures, and Ti6Al4V Cellular Structures. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.

(a) Backscatteredelectron (BSE) images showing the cross-sectional microstructures of laserremeltedAl-Sc-Zralloy;(b) highmagnification image showing laser remelted area A in(a); (c) high magnification image showing cast area B in (a); (d) EDS line scan revealing the compos