Fennec Foxes 3331 Aluminum Alloy Competition AU2024

The goal of this project was to identify and create an aluminum alloy that maximizes yield strength, elongation, and electrical conductivity. The final score is a product of these three properties, ranging from 0 to 100, with 100 being the highest measurement in class. A modified version of a 5000 aluminum alloy based on 5251 H18 and 5754 H14 was selected due to the consistently average values in the desired fields. The alloy consisted of 97.5 wt% Al and 2.5 wt% Mg with no additional alloying elements.

After casting, the billet was homogenized for 48 hours at 500 °C and then cut into two halves. The alloy needed to be worked to reach a final design thickness of 2-3mm. The first half was cold rolled in 1mm reductions and samples were cut after each reduction for hardness and electrical conductivity testing. A final thickness of 2.71mm was reached. The second half was cold rolled to a thickness of 2.6mm then cut in half and rolled to 2.03mm. Electrical and hardness tests were conducted on Zetec DC-2 and Buehler Wilson Rockwell 574 respectively.

Elements Given

1. Aluminum (Commercially pure aluminum piece and shot)
2. Copper (99.9% Cu shot)
3. Manganese (60% Mn - 40% Al)
4. Silicon (50% Al - 50% Si)
5. Magnesium (50% Mg - 50% Al)
6. Zinc (99.9% Zn shot)
7. Titanium (6% Ti in Al)
8. Chromium (20% Cr in Al)
9. Nickel (20% Ni in Al)
10. Iron (10% Fe in Al)

Elements Used

1. Aluminum (97.5% Al)
2. Magnesium (2.5% Mg)

The alloy consisted of 97.5% Al and 2.5% Mg with no additional alloying elements. The purpose of this was to maximize electrical conductivity by keeping the alloy as pure Al as possible, thereby reducing impurities and precipitates which hinder electron flow. The Mg was added to strengthen the Al and to keep as much ductility as possible.

750 grams of commercially pure aluminum was added to the crucible and brought to melt. 50 grams of 50/50 magnesium was measured and wrapped in aluminum foil to prevent violent spitting while melting. 200 grams, minus the weight of the aluminum foil, of commercially pure aluminum was added to the crucible. The 50/50 magnesium chunks wrapped in foil were added and the melt was stirred periodically to disperse the magnesium throughout the melt.

The billet was homogenized for 48 hours at 500 °C to evenly disperse the Mg throughout the Al, then cut into two halves. Based on previous data, cold rolling to final design thickness wasn't possible, rolling mill could overload. The first half was cold rolled in 0.5mm reductions in 2 passes per reduction, one pass to reduce the thickness and the second pass to reduce the internal stress of the sample. Samples were cut at every 1mm reduction to test hardness and electrical conductivity. This technique was used to aquire hardness data throughout cold rolling to get to the desired temper designation of H16, or 3/4 hard, sitting between the chosen alloy temper designations of H14 and H18. Two billets were cold rolled to different reductions without mill overload, the first billet was rolled to 2.78 mm and the second billet was reduced to 2.61 mm and 2.03mm.

Samples were collected from the as-cast, homogenized, and the 2.03 mm final thickness alloy. These samples were then mounted, ground down using silica carbide grit paper, then polished down to a mirror like surface.

Samples were mounted using Bakelite powder in a Beehler Simplimet 4000 Hot Mounting Press.

Once mounted samples were ground down using 4 grit levels of silicon carbide grit paper. For the as cast sample, first at 240 girt, the 320, 400, and finally 600 grit. Between each grit level sample was rotated 90 degrees. The homogenized and 2.03 mm samples were ground down using the same paper but at different girt levels. These samples started at 320, then 400, 600 twice, and finally 800 grit twice.

Our as-cast sample was polished in 3 steps. First it was polished at 6 micrometers, then 3 micrometers, and finally 0.05 micrometers with colloidal silica. The homogenized and 2.03 mm sample were polished at 6 microns, then 8 microns using microid diamond compound extender.

Electrical conductivity, hardness, and tensile testing was completed on the 2.03 mm and 2.61 mm thickness samples.

Max electrical conductivity of 40.95 at 2.78mm final thickness

Max hardness of 42.3 HRB at 2.61mm final thickness

Tensile testing

Max elongation of 0.031 at 2.61mm final thickness

Max yield strength of 265.04 MPa at 2.03mm final thickness

Once testing was completed, the team selected the 2.03 mm tensile bars to be used for competition. The final measurements of the alloy are:

Tensile Strength: 264.8 MPa

Elongation: 2%

Electrical Conductivity: 40.26% IACS

What we would do better in the future:

Fully homogenize alloy by increasing temp and duration.

Quench after homogenization to reduce magnesium diffusion within the aluminum, compared to slow cooling, to reduce unwanted dendritic formations, ultimately increasing elongation and yield strength.