Aluminum Alloys: Researchers Explore the Microstructure-Property Relationship in Metal 3D Printing

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300px-OSHlogoI’m always befuddled today by those on the periphery of the 3D printing industry who cry that the sky has fallen, and the technology is over and dead. We see either disappointment over the lack of 3D printers on the homefront (I thought we would all have one in our homes by now!), disdain for the learning curve involved in actually making things (this is too hard!), or impatience in seeing a true revolution that was supposed to send many down the tubes for good (what? The big companies we thought might crumble have been invested in 3D printing for decades?).

Many however, understand that instead of being ready to expire, in many ways 3D printing is still in its infancy. If you look around at what’s being produced, that’s obvious. While companies (and countries) may be stealing the headlines with everything from 3D printed cars and autonomous mini-buses to 3D printed office buildings, most everything is still in the initial stages, with much necessary refinement ahead.

3D printing with metal is a perfect example. While those on the outskirts are busy declaring it over, researchers around the world are just digging in deeper. The evidence would be hard to deny on any level as we see 3D printing with metal a huge priority in production facilities for giants like GE and Alcoa, and we see researchers looking into nearly every aspect of this materials science from porosity issues to issues with operator handling. Development and functionality of a range of metal alloys is at the top of the list for discussion and exploration, however, considering the strength and power 3D printing in metal materials can offer to manufacturers hoping to improve their products—and the bottom line.

Recently, researchers at Michigan Tech Open Sustainability Technology (MOST) Lab began working together on a project to explore the use of common aluminum alloys in 3D printing. ‘Structure Property Relationships of Common Aluminum Weld Alloys Utilized as Feedstock for GMAW-based 3D Metal Printing,’ authored by Amberlee S. Haselhuhn, Michael W. Buhr, Bas Wijnen, Paul G. Sanders, and Joshua M. Pearce was recently published in Materials Science and Engineering. Here, they begin exploring how microstructures and properties relate to each other in 3D printing.

UntitledAs they point out, 3D printing with metal is now being used to make components from jet parts and medical implants to jet engine fuel nozzles. Addressing the more common use of polymers due to affordability and accessibility, the research teams explains that metal 3D printing is currently used in the industrial sector with equipment that can cost upward of $500,000. With a focus on gas metal arc welding (GMAW), they explain that the technology is open to many more, and allows for much of ‘traditional welding literature’ to also be used in GMAW-based metal 3D printing, a method we’ve discussed previously from the same researchers in the matter of 3D printing with reusable substrates.

“3D printing via GMAW most closely resembles single-layer, multi-pass welding, also known as multi-run welding. This type of welding process reheats previously welded material, thus altering the grain structure, which can improve weld mechanical properties such ductility while reducing residual stress,” state the researchers in their paper.

“Although GMAW-based metal 3D printing is analogous to single-layer multi-pass welding technology, 3D printing with this technology requires special considerations since the weld material comprises the entire part, rather than a small portion. This results in a unique distribution of thermal stresses, microstructures, and mechanical properties as a function of process parameters and part geometry.”

The key here is that GMAW is more affordable, allowing for a gas-shielded metal wire to be fed through a nozzle heated up by an electrical arc.Untitled

Looking specifically toward aluminum, the focus is on how new materials can be developed, ultimately, resulting in new processes and products. The team examined aluminum weld filler in terms of tensile, compressive, and microstructural properties. Alloys examined were:

  • ER1100
  • ER4043
  • ER4943
  • ER4047
  • ER5356

In their alloy test specimens, using an open-source GMAW-based metal 3D printer, the research team found porosity in all to be under two percent, with the 4000 series proving superior to both 1100 and 5356 in terms of:

  • Printed bead width
  • Porosity
  • Strength
  • Defect sensitivity

For bead width, the research team saw 1100 as the smallest, and then followed by the 4047 and 4043 alloys.

“The two alloys with magnesium additions, 4943 and 5356, exhibited the largest bead widths and were statistically equivalent,” said the researchers.

1100 and 4043 offered less porosity that the other aluminum materials, while according to the research team, 5356, a high magnesium alloy, showed the greatest porosity.

They pointed out that in durability, differences in tensile strength in both 1100 and 4047, indicating bottom specimens showing less strength than those of the top.

“In elongation, the bottom specimens of 1100, 4943, and 4047 were all less than the top specimens,” stated the team.

Untitled

Tensile fracture surfaces of 3D printed aluminum alloys. Note macro-coning in the 1100 specimen and the region of brittle fracture in 4047

Macro-coning was displayed in the 1100 ‘tensile specimens,’ while in the 4047 alloys the researchers observed areas of brittle fracture. The 5356 specimens also showed cracking, which was attributed to the barriers between print layers.

“All fracture surfaces also exhibited higher than average bulk porosity, likely resulting from material failure at locally weak regions having the highest concentration of defects,” stated the team.

Overall, the 4000 series was found to be superior, from bead width and porosity to tensile strength.

This study is valuable in that it offers the researchers more knowledge in their journey to study metal 3D printing with their open-source GMAW technology, as well as offing useful information for their peers, and engineers, as they move forward to make new components with new materials in additive manufacturing. There is not a lot of research in this area of structure-property relationships so far, but what they were able to conclude in these experiments was that aluminum—and especially the 4000 alloy—could be considered equal to other materials, and most likely, out-performing for 3D printing. Discuss further in the Aluminum for 3D Printing forum over at 3DPB.com.

[Source: Academia]

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