Ninja Lantern Sharks 6016 Aluminum Alloy Design Challenge

The Ninja Lantern Sharks were tasked with researching, casting, and testing and aluminum alloy to meet the following competition requirements:

• Maximize 0.2% offset yield strength (YS)
• Maximize total elongation (%EL)
• Maximize electrical conductivity
• Alloy must contain 90% Al
• Thickness of final sample must be 2-3mm

• 2 grams of pure zinc
• 10 grams of 50% magnesium 50% aluminum alloy
• 25 grams of 50% silicon 50% aluminum alloy
• 963 grams of commercial purity aluminum
• Induction furnace
• Metallography equipment
• Inverted optical microscope
• Furnace capable of reaching 600 degrees Celsius
• Tensile testing frame with extensometer
• Electrical conductivity tester

Alloy Selection: Al 6016

The decision to opt for Al 6016-T6 was driven by its impressive combination of properties that aligned well with the specific requirements for our competition. The aluminum alloy is known for its excelent elongation and conductivity, making it a good choice for the requirements of this competition.

Elongation and Electrical Conductivity

Because of the requirements of this project, there was an emphasis on selecting a material with good elongation and electrical conductivity. Elongation is crucial when a material is subjected to deformation and stress, the material's ability to remain ductile and withstand the force. In our case, the ability to recover elongation after working was important, thus Al 6016-T6 was a standout choice.

Similarly, conductivity ensures efficient electrical performance. Unlike certain attributes that can be enhanced through thermomechanical processing, conductivity and elongation are tied to the material's composition. The material's ability to keep such high electrical conductivity readings even after extensive working was a key factor in our selection.

Zinc Addition for Preciptiation Hardening

To further enhance our alloy's mechanical properties, our team opted to introduce zinc into our material composition. Zinc improved the precipitation hardening of the material. As well as this, it also contributed to improving the overall strength of the material.

Compromise and Yield Strength

Knowing that it would be difficult to find a material that excelled in all categories of the competition, the team made a deliberate compromise to go with an alloy with slightly lower yield strength. This decision was reached because of the consideration of the project requirements, and balanccing the need for workability. The team also thought that the addition of zinc would also gradually increase the yield strength.

Target Composition

The team decided on Al 6016-T6 because of is high aluminum content, 97.5%. The alloy was fortified with the following: magnesium (Mg), silicon (Si), and zinc (Zn). The target composition is as follows:

• Mg: 0.5%
• Si: 1.25%
• Zn: 0.2%

Thermomechanical Processing of Al 6016

When it came time to being working our alloy, our team was strategic when selecting the thermomechanical process for the alloy. The team's goal was not just to meet but surpass the mechanical properties of standard Al 6016. Our expected mechanical properties is as follows:

• YS: 110-210 MPa
• Elongation: 11-20%
• Electrical Conductivity: 48-54%

TMP Process: Step-By-Step

1. Casting: The alloy was casted into the desired shape using the standard casting methods.
2. Homogenization: The team started with homogenization, with the goal of achievig compositional uniformity. This step eliminated any irregularities, and established a baseline within the material.
3. Mechanical Processing: The team chose to hot roll and cold roll the material to increase the mechanical properties. The team intended to reduce the material by hot rolling half of the way and cold rolling the other half until the desired thickness is acheived.
4. Solution Heat Treat: The team intended to use a standard heat treatment process for a T6 temper. This process heats the sample to a specific temperatue, and sustaining it at that temperature for a period of time. This process dissolves any precipitates present in the material, and tranforms it into a single phase structure to improve overall strength.
5. Aging: The team chose to age the samples for a variety of time to make selecting the competition sample easier. The aging process was executed under controlled conditions, which ensured the material aquired the desired strength and durability.

Casting

The team's decision on what to add to create the desired alloy was debatably the most important part of the alloy competition. The team measured and combined the specific materials according to stnadard casting procedures. The team aimed to create an alloy that would have high conductivity and strength, and the additions to the aluminum were an integral part of that. The measurements of each material is as follows:

1. 963 grams of commercial purity aluminum
2. 2 grams of pure zinc
3. 10 grams of 50% magnesium 50% aluminum alloy
4. 25 grams of 50% silicon 50% aluminum alloy

Homogenization

Subsequent to the casting process, the alloy underwent a homogenization state. The material was heated to 580 degrees Celsius for 24 hours. This was done to achieve a uniform microstructure that was rid of any stresses or uneven distribution throughout the material. The first image is the as-cast microstructure 100x and the second is the homogenized microstructure 100x. The third image is of the team pouring the alloy to cast.

Hot and Cold Rolling

The original sample was 12.5mm thick, meaning that the sample would be hot rolled to reduce 6mm and cold rolled to reduce 4mm, leaving the final thickness of the sample at approximately 2.5mm. After hot rolling, the first sample measured 6.34mm and the second measured 6.32mm. This process was chosen in an effort to maximize the benefits of both hot and cold rolling. Each pass for hot rolling redecued approximately 1mm, and cold rolling reduced 0.1mm with each pass. The team did observe some slight cracking along the edges after cold rolling. The first image is a 50x micrograph of the cold rolled sample. The second image is of the two samples after rolling.

Solution Heat Treating

Following the casting and homogenization phases, the alloy was subjected to a solution heat treatment to enhance the alloy's mechanical properties. The material was heated to 500 degrees Celsius for 1 hour. Immediately following the heat treatment, the sample was quenched. The sample was immersed in water. The cooling rate ensured the retension of the microstructure achieved during the solution heat treatment.

Artificial Aging

The samples underwent an aging process within a controlled environment, in an oven set at a temperature of 190 degrees Celsius. The samples were taken out throughout the process at hour 0, 1, 2, 3, 4, and 5. The slection of the specific temperature and duration aimed to change the material's microstructure gradually. Testing along the way allowed the team to select a sample with optimal test results, in regard to its mechanical and electrical properties. The team chose to strike a balance between enhancing the alloy's characteristics and mitigating any drawbacks that the thermal process could introduce. The team measured the electrical conductivity after the solution heat treatment and aging process.

The first image is a 100x micrograph of a solution heat treated sample with no aging. The second is a table with the conductivity ratings.

Data Observation and Predictions

The modulus of elasticity increased slightly at 2 hours for both samples. The samples had decreased elasticity observed at hours four and five. The yield strength had varied results throughout the aging process. There is an initial increase at hour 1 for both samples, followed by another slight increase at hour 2 and peaking at hour 3. Once again, a decline is seen after hour 4 and 5. Maximum stress mirrors the trends seen in yield strength, with a significant increase at 2 hours and peaking at hour 3. Values remained elevated at hour 4 and 5, which was not observed with the yield strength and elasticity. Elongation at fracture demonstrates a consistent decreasing trend throughout the duration of the aging process, notably at hour 3, and continuing throughhour 4 and 5. The team decided to use a sample that had aged for 4 hours due to its heightened elongation and conductivity results.

Tensile Testing

• Two samples from each aging process (0-5hr) were taken
• YS peaked at 4 hours of aging with an average value of 231.522 MPa
• Elongation peaked with no aging and had an average value of 15.8%

Ideal Sample for Competition

• The 4hr aged sample is the ideal sample
• Higher elongation and yield strength was prioritized
• Electrical conductivity was high for all samples

The first graph is the compiled data set for the recorded YS over time. The second is the total elongation at fracture over time. The table is a compliation of the team's testing data before selecting the competition sample.

The team's final score was 523,410. The electrical conductivity of the competition sample were higher than the expected results, measuring 51.3 %IACS. The elongation also exceeded the team's expected results and measured 6.7% at fracture. Both electrical conductivity and elongation scored the highest among the teams in the competition. The yield strength result was significantly lower than the team expeced, measuring 205.7 MPa. This was lower than the target by almost 30 MPa.

Process

• Homogenization for compositional uniformity
• Mechanical Processing to shape and build strength
• Solution heat treat for more strength and ductility
• Artificial aging 

Results

Yield Strength:

• Below theoretical expectations
• Fell below other teams competing
• Consider reevaluation of composition and aging

Elongation:

• Top-ranking among other teams
• Performed slightly below target range

Electrical Conductivity:

• Highest competition score
• Fell within expected range

Conclusions

Our team's alloy performance on competition day was still impressive despite the shortcomings with the alloy's yield strength. The team managed to compete against the other teams, many of whom selected 7000 series alloys. While our electrical conductivity and elongation scored higher than many of the teams, the yield strength was difficult to beat against the other team's stronger alloys. Given that the alloy the Ninja Lantern Skarks selected is known for its conductivity and ductility, we would consider the competition a success.

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