Team Sharkbait's Aluminum Alloy - Aluminum Alloy Design Competition

We cast a 2224 Aluminum alloy which contains magnesium, manganese, chromium, titanium, copper, zinc, silicon, and iron. The objective of this cast was to create an alloy that would have a good percent elongation, yield strength, and conductivity compared to other Aluminum alloys cast for the competition.

Supplies

Aluminum

Magnesium

Manganese

Chromium

Titanium

Copper

Zinc

Silicon

Iron

Crucible

Ingot mold

Furnace

Load rolling machine

Step 1: Casting

The elemental metals were weighed out to its proper proportions using Excel, as seen in the table. Magnesium and Zinc were wrapped in high-quality aluminum foil to promote mixing in the melt. The base aluminum was added to a preheated crucible at approximately 660.3°C. The alloying elements were then added to the melt to form a homogeneous mixture. The ingot molds were then preheated using a torch before the liquid alloy was poured and cooled.

Step 2: Homogenization

The cast ingot was sectioned into two samples for homogenization. One sample was placed into a furnace to homogenize at 535°C for 16 hours, and the second sample for 24 hours.

Step 3: Hot Rolling

Samples were hot rolled at 450-475°C until they reached an 80% reduction. 7 passes were performed on the 16hr homogenized sample and 8 passes were performed on the 24hr homogenized sample.

Step 4: Cold Rolling

Samples were cold rolled at room temperature until they reached a desired thickness of 2-3mm.

Step 5: Solution Heat Treatment and Quenching

Rolled samples were cut into 3 sections before being placed in a furnace at 450°C for an hour. Samples were then removed and immediately water quenched to room temperature.

Step 6: Aging

Samples were placed in an oven at 190°C for varying lengths of time. The sections of 16-hour homogenized aluminum were aged for 6 hours and the 24-hour homogenized aluminum was aged for 10 hours. Samples were then cooled at room temperature before being cut into tensile bars.

Step 7: Metallography

Samples were mounted with Bakelite powder using a mounting press at elevated temperature and pressure. These mounts were ground on wet silicon-carbide of increasing grit from 240 to 320 to 400 to 600. They were polished on a 6um polishing cloth lubricated with diamond extender fluid, then moved to a 3um cloth with diamond extender fluid, then 0.05um polishing cloth lubricated with colloidal silica.

Step 8: Conductivity Testing

A small section of both the 16hr homogenized 6hr aged and 24hr homogenized and 10hr aged samples were tested. 11 values for each sample were taken, and then averaged to provide an approximate value for conductivity, as seen in the table.

Step 9: Tensile Testing

A precut tensile bar was first measured for thickness, length, and width. The tensile bar was loaded into a Univeral Testing Machine (UTM), and values were inputted. An extensometer was placed on the sample and the UTM was run until fracture. Data points were logged and plotted using a TW Elite software. Samples were removed and the UTM was returned to zero before loading a new sample. Tensile testing was repeated for a total of 6 bars, 3 of each sample.

Step 10: Hardness Testing

The samples used for conductivity testing were used in a microindentation hardness tester. A Rockwell B scale was used to measure the hardness. 10 tests were run and the results were averaged to find the estimated hardness of each sample. Each indent was made with sufficient spacing from previous indents to get accurate results.

Step 11: Final Testing and Results

Conductivity and Tensile testing steps were repeated. The plotted values for stress vs. strain are seen in the image. The final results of our alloy were a Yield Strength( with 0.2% Offset) of 226.861 Mpa, a Maximum Stress of 354.8 Mpa, and an Elongation of 6.5%. This alloy performed very close to the predictions and placed last in the Aluminum alloy competition.