## 1 Introduction  
Metal foams are a relatively novel family of technical materials that mimic the structure of porous natural materials such as coral, bone and sponge [1]. Foam can be produced from a myriad of different metals such as steel, alloys of titanium, nickel, magnesium, copper, aluminum, etc. The latter of these materials is most commonly used in the foaming process due to its low melting point, good mechanical properties, high corrosion resistance, recyclability and low weight. Porous structures provide a unique combination of properties such as: low weight, high strength to weight ratios, great thermal, sound and vibration-insulating properties. These properties have led to the implementation of metal foams in naval, aerospace, biomedicine, chemical and many other industries [2; 3; 4]. The highest exploitation potential of metal foams can be found in the transportation industry, where they are used as passive safety elements due to their high energy absorption qualities [5; 6; 7]. One of the common ways of producing metal foams involves using metal powders and a foaming agent. Combustion of the foaming agent, most commonly titanium hydride (TiH\({}_{2}\)) or calcium carbonate (CaCO\({}_{3}\)), expels high amounts of gas into the base molten metal, which enables the formation of closed cell foams. The need for expensive metal powders and added costs associated with obtaining and implementing foaming agents in the production process leads to high production costs of metal foams [8]. According to the Aluminum Association, aluminum is one of the most recycled materials in use today. Approximately a third of today's newly produced aluminum originates from recycled aluminum alloys [9; 10]. Recycling aluminum alloys uses only 5%of the energy needed to separate pure aluminum from its ore. Aluminum recycling is not without its drawbacks, as it is estimated that up to 38% of the input material is lost during conventional recycling. These high loss rates are credited to burning and slag mixing during the recycling process itself [11]. Taking material loss and input costs into consideration, some authors have assessed the viability of using scrap aluminum alloys in the production of functional metal foams. Scrap metals produced by conventional machining methods, such as milling and turning, have great potential to be recycled into porous materials as this production route could significantly reduce manufacturing costs by bypassing the need for expensive metal powders. Most of the foams produced via the scrap metal route are closed cell foams using TiH\({}_{2}\) as a foaming agent. In papers written by [PERSON] et al. [12] and [PERSON] et al. [13], aluminum A380 (EN-AC46500) closed cell foams were produced by recycling discarded milling chips. In their papers, discarded milling chips were first mixed with TiH\({}_{2}\) powder, then cold and, eventually, hot extruded to produce a foaming precursor. The precursors were then foamed in a furnace to produce closed cell aluminum foams. [PERSON] et al. [14] used titanium hydride and aluminum oxide as foaming agents to produce AA 6063 aluminum metal foams from scrap metal. Their research showed that the porosity of the foam increases with an increase in TiH\({}_{2}\), while adding aluminum oxide into the mixture has a beneficial effect on the expansion of the foam. [PERSON] et al. [15] made foams using scrap from four different aluminum alloys and TiH\({}_{2}\) and calcium carbonate, CaCO\({}_{3}\) as foaming agents. Their research showed that foams produced using TiH\({}_{2}\) had a lower relative density and were more homogeneous than foams produced with CaCO\({}_{3}\). Their findings also showed that alloy type has a significant influence on the production of foams. [PERSON] et al. [16] measured the electrical resistance of aluminum foam produced from scrap material. Their research showed that porous materials have a higher electrical resistivity than dense forms of the same alloy.