Effect of B₄C amount on the microhardness of AA7075/B₄C composite metal foam.

Abstract

In this study, the polymer replication method was applied to obtain metal foam from composite powders produced by the mechanical alloying by adding different amounts of B₄C (5, 10, 15 wt.%) to the AA7075 aluminum alloy matrix. The corresponding AA7075 aluminum alloy and B₄C powder ratios were mechanically mixed in a planetary ball mill for 300 min for the composite powder preparation. Afterward, the composite metal foam was produced from mechanically alloyed composite powders, with polyvinyl alcohol (PVA) as a binder, polycarboxylic acid as a dispersant, distilled water, and a polyurethane sponge template with a linear cell number of 25 PPI (Pores Per Inch). The effect of the amount of reinforcement on the microhardness of the composite metal foam was then analyzed. DTA/TG/DSC analyzes were performed on aluminum composite powders and polyurethane foam to determine the sintering temperature suitable for the composite foam and the combustion temperature of the polyurethane foam. Thermal treatment was carried out to strengthen the foams produced. To this end, the model material was removed from the structure, and then sintering was carried out at 650 °C for 3 hours. The characterization and morphological analysis of the foams produced was carried out using the XRD and SEM/EDS methods. It was observed that apart from α-Al and B₄C phases, secondary and tertiary Al₃BC, AlB₂, AlB₁₂C₂, and A_l3B₄₈C₂ phases were formed as a result of the sintering process. The results of the EDS analysis showed the presence of elements O, except for elements Al, Zn, and Mg belonging to an AA7075 alloy and elements B and C belonging to the reinforcing element. Densities of composite metal foams produced with a solids content of 60% were measured between 0.12–0.15 g/cm³, and their porosity values were calculated between 90.4–95.5%. The study's findings allow stating that the increase in hardness was directly proportional to the rise in the amount of the reinforcing agent. The highest hardness was 28 HV in composite metallic foam with an additive of 15% B₄C by weight.