BS in Materials Engineering
Materials Engineering Department
The analysis of die-cast 380 aluminum-boron carbide particulate metal matrix composites (MMC) was performed in order to see if the samples had the required tensile strength of 300 MPa. 10wt% B4C die-cast samples were produced and tested. Half were heat treated to the T6 condition and the others were left as cast. Using ASTM standard B 557M it was found that the average tensile strength for the as-cast samples was 130 MPa and the heat treated samples had a tensile strength of 93 MPa. These values were both lower than expected. The heat treated samples were not expected to have a lower tensile strength than the as-cast samples. Since hardness is related to tensile strength, microhardness values were obtained to see if there could be an explanation for the unpredicted tensile data. The non-heat treated samples had an average hardness of 114 HV while the heat treated samples had an average hardness of 123 HV. A two sample t-test failed to prove a significant difference in the microhardness values of the two separate treatments. With no conclusions being able to be drawn from the hardness data, metallographic samples of each treatment were produced to examine the microstructure of the material. Both samples showed that the B4C particles were not homogeneously distributed; there were highly concentrated regions of B4C particulates. In addition, both were highly porous. From this information, it was inferred that the weakness was due to fracture initiation at these regions. In order to gain the strength desired it will be necessary to have a more evenly dispersed reinforcement as well as reducing the porosity.