Nano-deposition on 3-D open-cell aluminum foam materials for improved energy absorption capacity

Open cell aluminum (Al) foams have been used as energy absorbers for decades. Their energy absorption capacity can be enhanced by thickening the foam struts, or increasing the foam's relative density. However, the enhancement is compromised by the inherent characteristics of its stress-strain property relationship, whereby upon homogeneous strut thickening, an increase in the plateau stress without a reduction in densification strain cannot be achieved. In this work, to overcome this inherent barrier, nano-crystalline copper (Cu) was deposited onto the Al foam and novel 3-D Cu/Al, heterogeneously thickened, composite foam structured materials were fabricated and tested for the first time. A non-cyanide nano-crystalline copper electro-deposition system was setup for the coating of open-cell Al foam, and, the energy absorption capacity as a function of foam pore size and Cu coating thickness was investigated. A variety of characterization methods confirmed the nano-crystalline structure of the Cu deposition (38 nm). The energy absorption capacity of Al foams (with average strut thickness of 192 μm) reinforced with a 60 μm Cu coating was 3 times greater than that of plain foams. The compressive stress-strain response of the composite samples showed no significant reduction of the densification strain compared to the uncoated foams due to the small change in the foam strut thickness and pore size. A comparison between thin Cu-coated and uncoated Al foam samples with the same overall strut thickness (i.e., same effective volume density and porosity) showed that the nano-reinforced foams had superior energy absorption capacity over plain foams with the same overall thickness, (∼2 times greater).