Aluminum Alloy Competition AA6022-T62

As part of MSE 3331 at The Ohio State University, our class ran an in-house Aluminum Alloy Competition built around sheet-type aluminum alloys. The objective of this project was to design, process, and characterize an aluminum alloy that achieves the best overall balance of yield strength, ductility, and electrical conductivity, rather than simply maximizing a single property.

To keep the design space realistic and relevant to industrial alloys, the competition imposed several constraints. Each team was required to use an alloy within the 1xxx–7xxx series, maintain at least 90 wt% Al, and produce a final sheet thickness in the range of 2–3 mm. After processing, each team’s alloy was mechanically tested and electrically characterized. For scoring, the highest value in each property (yield strength, elongation, and %IACS) was assigned a score of 100, and all other results were normalized relative to that value. The three normalized scores were then multiplied to generate a single performance index, so achieving a high score required a true compromise between strength, formability, and conductivity.

This competition was designed not only as a friendly challenge to see which team could obtain the highest score, but also as a way to connect processing, microstructure, and properties in a tangible way. Through casting, homogenization, hot and cold rolling, solution heat treatment, quenching, and subsequent mechanical and electrical testing, we were able to see how each processing decision affected grain structure, precipitate distribution, and ultimately the performance of the final product. In our project, we selected and optimized AA6022-T62 as our candidate alloy and systematically processed it to compete within this framework.

1. Aluminum (Al) – Base metal forming the primary matrix of the alloy.
2. Silicon (Si) – Key alloying element that combines with Mg to form Mg₂Si precipitates, providing significant age-hardening potential.
3. Magnesium (Mg) – Works together with Si to enable precipitation strengthening and improve yield strength.
4. Copper (Cu) – Minor addition that further enhances strength through additional precipitation, at the cost of some conductivity.
5. Manganese (Mn) – Promotes the formation of dispersoids that help stabilize the microstructure during rolling and heat treatment.
6. Iron (Fe) – Common impurity element in Al alloys; kept within a controlled range to limit detrimental intermetallics while maintaining realistic industrial composition.

The team used GRANTA to select this alloy. This software provides graph simulation of different aluminum alloys’ properties based on their alloying elements and thermo-mechanical treatment. AA6022 was chosen for several reasons

1. Forgiving processing requirements
2. It can tolerate some variation in heat treatment and rolling without completely losing its properties, and the low alloying content makes it less prone to cracks during casting.
3. Impressive mechanical properties (Figure 1 and 2)
4. Under T6/T62-type treatments, it offers automotive-relevant yield strength and ductility.
5. Its low alloying content (2-3%) is great for conductivity.
6. Less solute means higher electrical conductivity, which is critical for our scoring metric.

Aluminum : 96.7 – 98.7%

Copper : 0.1 – 0.11%

Iron : 0.05 – 0.2%

Magnesium : 0.45 – 0.7%

Manganese : 0.02 – 0.1%

Silicon : 0.8 – 1.5%

We prepared measured amounts of the alloy’s elements based on calculated composition and the total alloy weight. All the elements were added into a heated crucible and melted together. The molten material is then poured into a billet mold until it solidifies. A portion of this material was cut for metallography, providing a baseline “as-cast” condition. This casting step produces a fully solidified billet with the target global composition, from which all subsequent processing is carried out. By melting above the alloy’s liquidus temperature and briefly holding in the melt, the solute elements (such as Mg, Si, and Cu) are dissolved and mixed into the aluminum matrix, although some microsegregation and interdendritic second phases are still expected in the as-cast state. Recording this initial microstructure is important, because it allows us to directly compare how homogenization, rolling, and heat treatment later modify grain morphology, phase distribution, and ultimately the mechanical and electrical properties.

The homogenization process involved heating the cast sample to a temperature of 550˚C and leaving in an electric box furnace to diffuse for 48 hours. After homogenization, the alloy was cooled to room temperature. This step was performed to reduce chemical segregation from casting by allowing Mg, Si, and other solute atoms to diffuse out of the interdendritic regions and toward a more uniform composition. As a result, the coarse, uneven second phases present in the as-cast microstructure begin to dissolve or spheroidize, producing a more homogeneous matrix that improves hot workability and leads to more uniform grain structure and mechanical properties during subsequent rolling and heat treatment.

The photos above show the result of the homogenization treatment, one with etch to reveal the grain structure, and one without etch. The homogenization successfully created a uniform composition with fine precipitates and small equally sized grains.

The team took a piece of the as-cast and homogenized samples for metallography. The metallography process involved three main steps:

1. Mounting
2. Place samples into Buehler Simplimet 4000 hot mounting press
3. Added Bakelite powder.
4. Grinding
5. ground on 240, 320, 400 and 800 grits.
6. Polishing
7. 6 µm and 3 µm diamond paste with diamond extender
8. 1 µm colloidal silica polish

Finally, the samples are then etched with 2% Nital.

The samples were hot rolled to decrease the size of the grains and get the as-cast alloy closer to the required thickness. Hot rolling allows for larger reductions since the metal is more flexible and will recrystallize at high temperatures, which is why it was done before cold rolling.

First, the sample was cut into two pieces to fit the width of the roller. Two homogenized samples were hot rolled at 480˚C. The target reductions were 70% and 80%, respectively. The first sample had 7 passes and reached a final thickness of 3.48 mm, while the second sample had 5 passes to reach 3.17 mm.

The two hot rolled samples were then cold rolled to varying percents of reduction. Sample #1 was reduced from 3.48mm down to 2.79% for a ~20% reduction. Sample #2 was reduced from 3.00mm down to 2.77mm for a ~10% reduction.

The samples seemed to curl upwards after each pass and for Sample #1 the final pass took the curled and wavy bar and almost completely flattened it which we assumed to be attributed to the grain structure becoming so elongated that it started to break down and release the internal stress of the sample. Sample #2 was only reduced by 10%, so it did not undergo this phenomenon.

After rolling and Solution Heat Treatment and Quenching, the homogenized samples were measured for their hardness and electrical conductivity. Hardness was measured by placing the cross section under Rockwell Hardness Tester, which calculates hardness by pressing an indenter into the surface of the material being tested, under a known load. Electrical conductivity was measured by lightly pressing an electrical probe on the material’s surface.

Post Rolling Results:

1. Average 1st sample Post Rolling
2. 89.1 HRH
3. 54.02 %IACS

1. Average of 2nd sample Post Rolling
2. 87.0 HRH
3. 54.47 %IACS

The group carried out optical microscopy throughout the process of designing the alloy so that we could visualize the effect that each treatment had on our alloy. We completed metallography and microscopy on the alloy after the homogenization treatment, and after the rolling process.

The two samples were each cut in half and labeled Sample #1a – Sample #1b and Sample #2a – Sample #2b. All the samples were heated to 560 Celsius for an hour. The “a” samples were quenched in water and the “b” samples were quenched in oil (specifics of oil unknown). The reason for the differing quenchants was to test if slowing the cooling rate with oil would change the mechanical properties of the samples.

All samples were then artificially aged at 176 Celsius for 6 hours.

The solution treated samples were then milled into tensile bars. Each bar was then placed into tensile machine that applied certain axial loads. An extensometer was attached at the center of the gauge to measure the strain. Data files were generated in an excel form with the sample’s yield strength, elastic modulus, and strain.

Because we tested both water and oil quenched samples, we observed two different performance profiles.

1. The average yield strength and strain of the water quenched samples were 283.53 MPa and 8.72%.
2. The oil quenched samples averaged 258.6 MPa and 8.6% strain.

While the impact on ductility was minimal, the difference in yield strength was significant. This result was somewhat expected, as a slower rate of cooling gives our alloying elements more time to form large precipitates which isn’t favorable. Still, the team wanted to confirm the theory and try the oil quench anyway. Based on the results, the team selected sample 2 water quenched samples as the final submission to the alloy design competition, since it maximizes yield strength and ductility.

The final performance of the tested sample was about the same as our previous tests, with slightly less % elongation. Overall, the team finished in 3rd place, and we achieved properties that only fell slightly short of our target properties that we had when selecting the alloy.