This document summarizes research on analyzing the microstructure of aluminum-based high entropy alloys through optical microscopy. Key results showed that heat treating alloys to dissolve secondary phase precipitates produced stronger alloys with higher ultimate tensile strengths. Future work will develop new aluminum alloys with different elemental combinations to find superior mechanical properties. Optical microscopy is a useful tool for analyzing alloy microstructure and correlating it to mechanical properties like strength.

1. Microstructure Analysis of Aluminum Based High Entropy Alloys
BACKGROUND RESULTS RESULTS
CONCLUSIONS AND FUTURE WORK
REFERENCES AND ACKNOWLEDGEMENTS
Allison M Silvia1, Gabriela A Chong2
Advisor: Dr. Yu Zhong1 Co-Advisor: Dr. Mohammad Asadikiya1
1Department of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA, 2Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, MA
METHODS
EREE
An alloys microstructure is directly related to its
physical properties, such as the strength of the alloy.
Secondary phase precipitates:
• Undissolved molecules
• Form their own lattice structure
• Cause lattice distortions
• Locally changes the stiffness at those locations.
Heat Treatment: To reduce the amount of secondary
phase precipitates, heat treatment can be used.
Temperatures of up to 470̊ C are high enough for the
molecules to properly dissolve into an FCC lattice,
leaving little precipitation, and thus a stronger alloy.
Conclusion: Optical microscopy is a tool that can assist
in analyzing an alloys microstructure. Since an alloy’s
microstructure is directly related to its mechanical
properties, conclusions can be made about the alloy’s
strength from microscopic images.
Future Work: Our research group will continue to take
the concept of HEAs and apply them to new aluminum
alloys. With different combinations of elements, we can
find new alloys with superior mechanical properties.
Quelle, Kathryn Anne. “Exploring High-Entropy Alloys.” Department of Mechanical
Engineering, Carnegie Mellon University, 6 Nov. 2018
The project team would like to thank our sponsors, EREE, WIN, and
the ACRC, and the individuals who helped and assisted us throughout
our project. A special thanks to Davis Ladd, Connor Lemay, Dr.
Mohammad Asadikiya, Michael Collins, and Dr. Yu Zhong
Figure 3 (200 μm scale)
This is a photo of the
Al-4Zn-4Mg as cast alloy.
You can observe secondary
phase precipitates
throughout the sample as
well as pores.
Figure 5 (100 μm scale)
This photo shows the Al-
4Zn-4Mg two step alloy.
There are some pores seen in
the upper left but there are no
signs of secondary phases
due to heat treatment.
High entropy alloy (HEA):
• Alloy typically consisting of
five elements each at 5 – 35
mol %
• A solid solution in which
different atoms are randomly
located at lattice sites
• Form a crystalline structure
• Have improved mechanical
properties
Objective: Use the concept of an HEA to create an
aluminum based alloy with superior mechanical
properties.
Our project slightly differed from a traditional HEA
since our alloys are composed mostly of aluminum and
contain less than five elements.
Alloys that were continually heat treated preformed better
in tensile testing due to less secondary phase precipitates
Figure 1:
An HEA crystalline
structure
Sample preparation:
• Cut a slice of the alloy
• Mount inside clear resin
• Polish sample
The finished sample is then
placed under a microscope to
observe its characteristics.
Through optical microscopy, we
can observe grain boundaries,
pores, and secondary
precipitates in the sample.
One of the methods used to analyze a new alloy is to
study the alloy’s microstructure through optical
microscopy.
Figure 2:
Mounted samples before
polishing
Figure 4 (100 μm scale)
This is a photo of the
Al-4Zn-4Mg 1 step alloy.
You can observe secondary
phase precipitates around the
edges of the sample but at a
lesser consistency than the as
cast alloy.
As Cast 1-step
2-step
Alloy UTS (ksi)
As Cast 37.21
1 Step 40.22
2 Step 51.21