1. Thresher Industries is a zero discharge operation, we are an Earth Friendly manufacturer.

2. Thresher Foundry alloys are secondary ingot based alloys, 100% recycled aluminum is used in our alloys.

3. The Eco Core uses no binders and is based on an inert material and is 100% recyclable.

4. Our product mix includes neutron absorbing material used in casks for spent fuel rod in nuclear containment facilities and high strength metal matrix composite planter wheels for the agricultural industry. We are developing personal armor material as well as aftermarket components for transmission rebuild kits. Military contracts and driveshafts using our MMC's, as well as conventional aluminum castings for over the road truck air brakes.

THRESHER INDUSTRIES Composite Alloys

ThermaLite alloy is produced by Thresher Industries, using a proprietary method and equipment in our facility. The material has inherent strengths and weakness as does any material and should be used in applications deemed proper by the engineering using our data. Higher strength, abrasion resistance due to the ceramic particulate and lighter weight by volume contribute to its appeal. We use a simplified method of manufacturing allowing lower cost than competitive materials and we can cast the material into shapes typically used in both die casting and pressure casting. We offer a unique 'core' system for high pressure die casting allowing us to create one piece castings in hollow configurations using our composite alloy. Refer to the soluble core section of this site for detailed information on this process. The data presented here has not been certified yet and is raw but reliable data to be used as a baseline in engineering.

The gravity cast tensile samples were analyzed for microstructure and volume percentage of the reinforcement. Two samples from each level of reinforcement (5% B4C, 10% B4C, 15% B4C, and 5% fly ash) were created by cutting the top and bottom of the tensile sample (Figure 1). Regions 1 and 2 were initially chosen for analysis because the volume percentage of the reinforcement could vary due to density differences between the B4C particles and the aluminum matrix. The B4C has a density of 2.3 g/cm3 while the aluminum has a density of 2.78 g/cm3.

Evenly distributed particles will translate to more advantageous and consistent mechanical properties. In order to see if the gravity casting process is capable of producing the desired homogeneous microstructure the samples were imaged using optical microscopy.

5% B₄C

From visual inspection, the 5% B₄C had highly segregated regions of particles (Figure 2). The low percentage of particles provided fewer nucleation sites for grains to begin growing.

Due to this, a large amount of the aluminum-silicon eutectic structure formed (Figure 3). As shown in the micrograph, the light grey silicon blades tend to point in towards a segregated region of the B4C particles. The growth of these grains likely play a role in driving the particles into isolated regions. During a more rapid solidification process the growth of the grains would be reduced. This could lead to a more uniform grain structure and help mitigate the forces that are driving the particles to clump together.

10% B₄C

The 10% B₄C aluminum composite had a more evenly distributed crystal structure (Figure 4) than the 5% B₄C composite. While there are still conglomerations of particles, they are not as large as those found in the lower weight percent B4C composite. Due to the higher number of particles, there are more nucleation sites. With more grains being created, they impinge on each other much faster and do not allow for the B4C particles to be pushed by their growth. Even when magnified 500x it is hard to make out the small grains of the matrix aluminum.

15% B₄C

While more evenly distributed than the 5% B4C composite, the 15% B₄C composite has larger regions of segregation than the 10% composite (Figure 5). The increased number of nucleation sites creates finer grains in the matrix for reasons similar to the 10% B4C composite. The larger clumps could be caused by insufficient distribution of the particles during the initial melt. If there is too high of a volume percentage of the particles in the molten matrix, the stirring process will not sufficiently distribute them throughout the material. Additionally, there was more porosity in this sample than the other composites.

5% Fly Ash

The fly ash samples proved to be the hardest to analyze. Fly ash particles are generally cenospheres that range in size from 0.5 microns to 100 microns. Looking at the microstructure, there are only a few cenospheres apparent (Figure 6).

The optical microscopy would not allow for further magnification to investigate these particles. If the small particles are fly ash particles, then the distribution is homogeneous. Having information from the manufacturer about the approximate size of their particulates would aid in further investigation.

Volume Percentage Calculations

Using imaging software, I was able to determine the average volume percent of particulate reinforcement in each of the samples (Figure 7). It was found that there was no definitive difference between the top regions and the bottom regions. After taking a representative sample of images from each level of reinforcement, the average and standard deviations were found (Table I).

The table shows that the volume percentages are slightly higher than the weight percentages. This phenomenon is explainable due to the densities of the materials being different. Since the B₄C particulates are slightly less dense, the volume percentage will be increased. The standard deviation of the 5% B₄C composite was much larger than the others due to its highly segregated particulates.

Using the software does leave room for error. The software works by calculating the area of a chosen band of color wavelengths. In these samples, it was hard to single out one phase from the other because the colors were similar between the B₄C and the silicon phase.

Conclusions

1. 1. The 10% B₄C aluminum composite had the most homogenous dispersion of particulates.
2. 2. The 5% B₄C aluminum composite suffered from the most segregation of the particulates.
3. 3. The average volume percentage of the samples was slightly higher than the weight percentages used in processing, but this is explainable due to density differences.