Effect of biochar reinforcement on the mechanical and corrosion behavior of closed-cell aluminum foams

Aluminum foam, a lightweight, energy-absorbing material with excellent thermal and mechanical properties, could be used in aerospace, automotive, and structural industries. To improve properties such as strength, wear resistance, and corrosion resistance, biochar, a sustainable resource derived from biomass pyrolysis, could be used as reinforcement. This paper reports the first use of Conocarpus biochar to reinforce closed-cell aluminum foams via the liquid metallurgy route. The aluminum foam samples were produced with different weight percentages of biochar (1 wt.%, 2 wt.%, 3 wt.%, and 4 wt.%), with fixed percentages of optimized composition from our previous study, 3% CaCO₃, 1%Al₂O₃ (AF02). This study examined mechanical and electrochemical characterization, morphology, density assessment, microhardness, and specific wear rate. In this paper, it was observed that the average pore size gradually increases when biochar is added to aluminum foam; it goes from 2.077 mm in AFB01 to 2.649 mm in AFB04 (4% biochar), a 27.5% increase. However, incorporating 4% biochar produces foam cell collapse, leading to elongated pores and collapsed struts. XRD studies show the proper distribution and intermetallic compound formation in biochar-reinforced aluminum foam. When biochar is added to aluminum foam, samples AFB01 to AFB03 have a lower relative density and higher porosity. The porosity escalates from 78.9% (AF02) to 86.74% (AFB03), whereas the relative density reduces from 21.1% (AF02) to 13.26% (AFB03). The compressive strength of foam significantly deteriorates when the concentration of biochar increases from 1 to 3%. In comparison to the base sample AF02, compressive offset stress decreases by up to 43.4% (AFB03), plateau stress decreases by 66.7% (AFB03), and energy absorption decreases by 68.8% (AFB03). The incorporation of biochar notably enhances the corrosion resistance of aluminum foam composites. Specifically, AFB01 (1% biochar) demonstrates an 88.8% improvement, while AFB03 (3% biochar) exhibits a 72.2% enhancement compared to the base sample, AF02. Conversely, the specific wear rate of AFB03 shows a deterioration of 39.7% relative to AF02. In terms of microhardness, AFB01 displays a slight increase of 5.88%, whereas AFB02 and AFB03 exhibit negligible variation when compared to AF02.