Casting of recycled aluminum, Al + Cu + Mg alloy formation and lamination process of an electric current conductor

This research presents a methodology for the recycling process via casting, in which aluminum cans and primary (commercial) aluminum are transformed into a laminated tape, with the possibility of industrial application. This research was classied as bibliographic, exploratory, and experimental, since it used qualitative techniques to evaluate alternative materials. Its objective was to incorporate materials of different properties that could favor the making of a tape to be laminated. In the rst casting, a recycled aluminum ingot was formed only with aluminum from beverage cans and had a material yield of 51%. In a second casting, commercial aluminum was added to the recycled aluminum ingot. After the casting process with the two cast materials, the ingot had a yield of 90%. A third casting was conducted together with the aluminum that was already formed by the ingot (50% recycled and 50% commercial). The purpose of this ingot was to incorporate other materials that could provide some characteristics, such as malleability and conductivity. The third casting was made from the second ingot, and incorporated copper and magnesium. For the design of the laminated tape, a cast was made to receive the molten aluminum from the third casting. The aluminum was cast into this mold and three tapes were produced, one with a thickness of 2 mm, another with a thickness of 3 mm and the last with a thickness of 4 mm. With these tapes, the objective was to laminate them in order to reduce their thickness to values close to 0.5 mm. The casting process of aluminum cans with the addition of commercial aluminum, plus the incorporation of copper and magnesium, demonstrated facilities for thickness reduction in the process of making laminated tapes.


Introduction
Recycling is an economically and environmentally sound process. Its objective is to make use of waste that would be disposed of in land lls or in improper places, thus contaminating the environment (ABDEL-SHAFY; MANSOUR, 2018). With recycling, the volume of these wastes is reduced, as well as the amount of raw material used in certain processes (SHAMSUDIN et al., 2016).
With each ton of recycled aluminum, the extraction of 4 tons of bauxite is avoided. This saves up to 95% in energy production, which corresponds to approximately 700 kg of crude oil (ŠKŮRKOVÁ; INGALDI, 2014). When mentioning the term recycling, aluminum is the rst to come to mind because it is a material that can be recycled countless times without losing its characteristics (BDEIR; ALSAFFAR, 2008). Some of the bene ts of aluminum recycling go beyond the reduction of energy and the use of raw materials. Aluminum recycling involves social issues, since recycling is a source of income for many families of waste pickers, therefore, keeping people with a low level of education in the labor market. Thus, resources are generated for application in local economies, developing the market at local and national levels (FIGUEIREDO, 2009). According to Ghisellini and Ulgiati (2020), in Italy, recycling has become the preferred practice in most organizations involved throughout the supply chain, from post-consumer waste collection to secondary raw material recovery, recycling and production.
Aluminum recycling in Brazil has been growing in recent years. In 2002, the index was 87%, reaching 96% in 2005. According to the Brazilian Aluminum Association -ABAL (2018), almost all aluminum cans from beverages sold in 2017 returned to the production cycle, reaching an index of 97.3%. Of the 303,900 tons of cans distributed in the Brazilian market in 2017; 295.8 thousand tons were recycled. What separates aluminum from other waste is that it can be recycled without loss of physical / chemical properties. This makes it an excellent choice, especially for carbonated beverage packaging (e.g. soda and beer). The recycling process has one of its biggest advantages in saving energy, since it uses only 5% of the energy needed to produce the primary metal from ore

Recycling Aluminum Cans
The Brazilian city of Pindamonhangaba -SP stands out for its Industrial recycling of aluminum. In 2003, it was elected by the Brazilian Aluminum Association the national capital of aluminum recycling. Brazil's two largest aluminum recyclers are located in this city: Alcan (now Novelis) installed in 1970 and Latasa in 1996, which acquired the old Aleris Recycling Plant. Together, they process approximately 70% of all scrap recovered in the country (ABAL, 2017).
Compared to the primary aluminum production process, aluminum recycling has a 95% reduction in electricity consumption (ŠKŮRKOVÁ;INGALDI, 2014). Recycling activities play a role in conserving natural resources and reducing pollution. If waste is pre-treated and properly classi ed, recycled aluminum can be reused for almost all industrial applications (JERINA et al., 2018). Aluminum alloy recycling has grown in interest and applications in recent years and has become an economical, environmentally friendly and reliable way to produce aluminum parts (MANDATSY MOUNGOMO et al., 2016). In addition, Mansurov et al. (2018) state that the relatively low value of casting technology provides a greater share of the demand for aluminum alloys. This is besides aluminum's corrosion resistance properties and excellent recyclability.
According to Jerina et al. (2018), the quality of recycled material depends on several factors, including material purity, coating types and size. The control of impurities has a major in uence on the mechanical properties of recycled alloys. Similarly, Mansurov et al. (2018) mention that recycling causes individual and combined addition of impurity elements, such as Si, Fe, Cu, Zn, Pb, Sn, Ni and Mn, in the alloy casting properties (DAGWA; ADAMA, 2018). Another relevant factor, especially during the smelting process, is that scrap from urban recycling is generally oxidized. Jerina et al. (2018) state that the oxide content of large pieces of aluminum can reach 2% by weight. During the melting process, Al 2 O 3 oats to the surface and forms a second phase known as slag. In the process of melting aluminum scrap, about 10% of the material is lost because aluminum is mixed with slag and 10% of the metal is oxidized (GRONOSTAJSKI et al., 2000).
Iron is the most commonly found impurity element in aluminum recycling because it is very di cult to remove and gradually builds up through repeated recycling (BASAK; HARI BABU, 2016). Together with aluminum and other alloying elements such as manganese, copper, magnesium and silicon, iron produces intermediate phases, which are detrimental to the mechanical properties of the nal product during solidi cation. According to Ashtari et al. (2012), iron is one of the most problematic impurities in aluminum castings. According to Zhang et al. (2012), the addition of a suitable neutralizer such as Mn, Cr, Be, Co, Mo, Ni, V, W, Cu, Sr or other rare earth elements such as Y, Nd, La and Ce could control the deleterious effect of Fe in aluminum alloys (ZÁVODSKÁ et al., 2018).
The process of re-melting discarded cans has a prominence in the aluminum cycle production chain in Brazil (VERRAN et al., 2005). The can is composed of body, seal and lid, each of which is made up of different alloy compositions. The can body is made from ASTM 3004 aluminum alloy, the lid is made from ASTM 5182 alloy and the seal is made from ASTM 5082 aluminum (DAGWA; ADAMA, 2018).

Aluminum Alloys
The 3xxx series aluminum features corrosion resistance, good conformability and moderate mechanical strength. This alloy presents a higher manganese content, which is added to increase the corrosion resistance and ductility in aluminum (SCHLESINGER, 2013). In turn, 5xxx series alloys have a high magnesium content of up to 5.6%, which provides greater hardness, mechanical strength and corrosion resistance, as well as improved machinability and weld properties (BDEIR; ALSAFFAR, 2008). According to Davis (2001), the chemical compositions of the 3xxx and 5xxx series aluminum are described in Table 1.
The mechanical properties of the alloys used in aluminum cans are presented in Table 2.
The American Society for Testing Materials (ASTM) standard, which is used as a reference for can manufacturing, de nes the aluminum can in three different parts: body (alloy 3004); lid (alloy 5182) and seal (alloy 5082) as shown in Table 3.
In studies on aluminum can casting, Verran and Kurzawa (2008) performed tests with the addition of scorifying ux in order to optimize aluminum can casting and reduce slag formation in the process. Figure 1 represents the e ciency of the casting with the addition of scorifying ux and temperature evolution. It can be seen that e ciency stabilized with the addition of 10% by weight of scorifying ux and a temperature of 750°C. The addition of percentages greater than 10% by weight did not result in representative e ciency increases. Another factor to consider was the in uence of melting temperature, which resulted in a reduction in energy consumption and oxidation losses. Additions greater than 10% by weight improved the e ciency of the melt. However, there was a need to increase the temperature to 850 ºC. In addition, Verran and Kurzawa (2008) highlight the use of an induction electric furnace for casting, which has a better yield (71.61% average) when compared to combustion (oil / air) and gas furnaces, 55% and 60% respectively. Analysis of the chemical composition of the molten material is shown in Table 4.
There was a variation of Mg of 54.5% between maximum and minimum values. According to Kumar et al. (2018) magnesium, when subjected to high temperatures, undergoes variations in casting processes when in contact with oxygen, unless care is taken to protect the surface against oxidation. This protection occurs by the use of inert gas injection such as argon on the casting surface. Similarly, iron has a 72.5% variation between highs and lows. Contaminant elements such as Ti, Pb and Cr were found in small quantities in the recycled aluminum.

Aluminum recycling processes
According to Verran et al. (2004) in the small-scale aluminum can recycling process an induction electric furnace is used to melt the material. Then, the quality of the material collected and melted in the process is analyzed. The collected material at the beginning of the process is passed onto a conveyor belt. From there, the material is taken to a knife mill where the material is fragmented. The fragments move to an electromagnetic separator that removes ferrous materials that cannot be mixed with aluminum. Afterwards, the material passes through a hammer mill, where it is chopped into chips. Then, another magnetic separation also removes the residue of impurities. Next, the chips go through a vibrating screen that removes dirt, sand and other debris, and a pneumatic separator completes the process with air jets to remove paper, plastics and other contaminants. From there, the chips move on to the removal of inks and polymers that cover the material. This is conducted inside a rotary kiln, known as the oven kiln. Then, the chips are melted at 700 ºC, where the liquid material is poured into crucibles and transformed into ingots.

Alloy Elements
The addition of alloying elements adds characteristics to aluminum to provide the melt with properties of interest. Since the objective of this research is to produce a conductive laminated tape, it is relevant to add alloying elements such as copper, as its conductive properties are superior to aluminum. In addition, copper has better tensile strength and corrosion resistance, increased hardness, higher ductility and conformability (SHACKELFORD, 2008). Magnesium is another element that has properties that may favor the alloy composition to form the conductive tape. In addition to providing mechanical gains, magnesium allows the alloy to maintain a high level of corrosion resistance and weldability. However, magnesium is highly soluble at its melting point and it must be melted in an argon controlled atmosphere (ACHYUTH et al., 2019). Al-Mg alloys with contents ranging from 3-5% form alloys such as 5042, 5352, 5082 and 5182, which are used in the manufacture of beverage can lids (DAGWA; ADAMA, 2018).

Materials And Methods
This research used an experimental methodology and the recycled aluminum samples (beverage cans) were obtained through the Santa Cruz do Sul Waste Pickers Cooperative -RS -Brazil. To remove the moisture, the materials were inserted into a mu e furnace, with the temperature ranging between 150 and 200 ° C. The materials were melted without separation of the can components in an industrial Grion oven with the use of a steel crucible. The aluminum melting temperature was 750 ° C, based on Verran and Kurzawa (2008). The stages of the casting process that supported the methodology of this research are described in Fig. 2.
After the acquisition of the cans and their preparation for casting, the material was compacted and pressed. This allowed for better packing in order to provide better melting, since in a more compact load there is a lower surface / volume ratio, and consequently, a lower tendency for oxidation loss (slag formation).
The rst stage involved the casting of the aluminum cans and the formation of the 1st ingot. This was conducted by placing the cans in the oven manually, Fig. 3a. During the casting process, slag formed on the surface of the melt and was removed for every 5 kg of cans introduced into the oven, shown in Fig. 3b. At this stage of the research, 20 kg of recycled aluminum cans were used.
With the mixture nally homogenized, the melt was poured into the mold. For this step, the melt, while still in a liquid state, was poured in small quantities into the mold so that the mixture, when solidi ed, would not become too thick. Figure 4, 10.2 kg of melt was obtained from the total of 20 kg of cans, resulting in a 51% yield.
The second stage consisted of the commercial Aluminum Casting and incorporation of the 1st ingot to form the 2nd ingot. This step occurred through the casting of 10 kg of commercial aluminum classi ed as alloy 6063. When the material was in a liquid state, the ingots of the rst casting that came from the melting of the recycled cans were added. At the end of the homogenization of the mixtures, the material was again poured into a mold and converted into an ingot called the "50% / 50% ingot" (50% recycled cans and 50% commercial aluminum alloy). In this second casting, the mass yield was 90%.
From the aluminum ingot formed (Fig. 4) the objective was to create a 0.5 mm thick laminated tape. Since the ingot formed was 16 mm thick, it was necessary to produce a mold.
The third stage consisted of the incorporation of rice husk ash into the 2nd ingot and the formation of the 3rd ingot. In order to cast the 3rd ingot and start making the laminated tapes, it was initially necessary to cast the melt into a mold, which already had adequate spaces to receive the melt. Die casting has excellent dimensional accuracy and results in excellent mechanical properties. A at steel bar, SAE 1045, 30 cm long and 10 cm wide was used for its preparation. This bar was cut in half to use one piece as a lid and the other piece was milled with an 8 mm tool to form the channels through which molten aluminum and the rice husk ash, while still in liquid form, would be poured. This is presented in Fig. 5.
In the upper part of the two pieces of the mold, a cavity was made to prevent spillage of the aluminum from the third casting when it was poured (i.e. to direct material to the main channels). Regarding the pouring method, the gravity method was used. The three channels were made with 2 mm; 3 mm and 4 mm of depth. Thus, the specimens had their measurements described as shown in Table 5. For the out ow and exhaust of the gases, small diagonal cuts were made in the sides of the mold and interconnected the specimens. In addition, vertical outlet cuts were made at the base of the specimens for a directional exit at the bottom of the three channels.
Samples were taken for chemical analysis, micrograph, as well as density, impact and hardness testing to validate the mixture and verify properties.
The 4th Stage consisted of the incorporation of Copper and Magnesium in the 3rd ingot and thd formation of 2 mm, 3 mm and 4 mm specimens. After the formation of the 50% / 50% ingot, a third casting was necessary, since copper and magnesium were incorporated to the melt of the third ingot. This was done to discover which structure would have the best chemical composition for the tape. The third ingot was divided into 5 batches each being 800 g, as seen in Table 6 (1st sets of specimens). At the end of the 5 casting runs, 45 specimens could be selected and identi ed.
The furnace used for this experiment was a "well type" resistive furnace. The third ingot was introduced into the crucible and was given 20 minutes for temperature stabilization at 750 ° C. The mold was heated in a mu e resistive oven at a constant temperature of 350 ºC. The formation of the tapes occurred from the casting runs made from the 3rd ingot, which generated three specimens for each draining of the mold presented in Fig. 5. The starting point for the casting of each batch of samples of the experiment was the 800 g of aluminum that had already been incorporated into the rice husk ash in the 50% / 50% ingot.
A previous run was also carried out, which consisted of the aluminum casting of the rst ingot (50% commercial and 50% recycled), in order to verify how the formed aluminum alloy would behave. Figure 6 represents the casting of the aluminum formed by the rst ingot made in the mold. 800 g of aluminum was placed into the crucible inside the oven and when it reached a temperature of 750 ºC, 20 minutes were given to stabilize the melt.
Then it was poured into the mold, which was previously heated to 350 ºC. This is presented in Fig. 6.
After 5 minutes, the mold could be opened and the specimens were carefully removed to avoid fractures along the specimen (Fig. 7).
After each batch of samples obtained in the experimental sequence shown in Table 6, one sample was taken to conduct chemical analysis to identify the composition resulting from the proposed mixture in the experiment. This analysis was performed using the optical emission spectroscopy technique, performed by a CCD Plus -S5 Solar Optical Spectrometer.
It was determined that the manufactured mold achieved the objective of forming specimens closer to the nal thickness of the desired laminated tape (Fig. 8). In order to reduce the thickness of the specimens from 2 mm and 3 mm to 0.5 mm, it was necessary to perform the rolling process, in the order of, 4 x and 6 x respectively on the resulting thickness of the mold casting.
The 5th stage consisted of the rolling process of the specimens in the bench laminator and the formation of the laminated tapes. At this stage, after the selection of the specimens formed by those that presented a suitable structure to be laminated, lamination was carried out with the objective of reducing the thickness of the specimens formed and that were extracted from the mold.
The nal composition of the specimens after the addition of copper and magnesium can be seen in Table 7. At each run of molten material, 3 specimens were separated and the process was repeated 3 times in order to obtain the same specimen in triplicate, since each mold channel had a different thickness. The 6th step was conducted to con rm the thickness of the laminated tapes. At this time, the thickness of the laminated tapes was analyzed and only those with thicknesses less than 0.6 mm were selected. This value is very close to the thickness that was proposed at the beginning of the research, which was 0.5 mm. Some tapes, after being laminating 5 or 6 times, broke and could not be used as specimens. Only those that were unbroken, with more than 50% of their original size out of the mold, were counted as specimens.

Results
The initial mass of 20 kg, acquired at the Santa Cruz do Sul Recycled Materials Collectors Cooperative -RS-Brazil, after slag removal, resulted in a 10.2 kg cast aluminum ingot. In percentage values, the yield obtained in the process was 51% over the initial mass. It is noteworthy that the casting process was carried out in an industrial furnace with a combustion process that uses lique ed petroleum gas (LPG). The research by Verran et al. (2005) obtained an average yield of 71.61% through the use of an induction furnace. In addition, a scorifying ow was used in the process, which improved the yield to values above 80% when 20% by weight of scorifying ow was added.
For the chemical analysis of the composition of the cast aluminum ingot sample, which was composed of 50% recycled aluminum and 50% commercial aluminum, the optical emission spectroscopy technique was used. The results of the analysis are shown in Table 8: Comparing the data from the chemical analysis of cast aluminum with the data in Table 3, which shows the chemical composition of the aluminum can components de ned by the ASTM standards, it is clear that the silicon levels are equivalent and the other elements presented lower values in relation to the data in Table 3. A relative similarity with the data obtained by Verran et al. (2004) described in Table 9 is evident.
The results show that the aluminum contained a very close chemical composition. It should be noted that Verran et al. (2004) used only recycled aluminum cans. The percentages of manganese are below the reference table in Table 3. As for the other elements that appear in the form of impurities, it can be stated that the values found are within the limits allowed in all standards that de ne chemical composition speci cations for workable aluminum alloys.
Molten aluminum from aluminum cans was considered as the basic research element for the manufacture of laminated tape. Alloy elements such as copper and magnesium were added to this aluminum, which resulted from the second casting. The research evaluates whether these elements add improvements in the conduction properties of electric current in laminated tape.
With the addition of alloying elements, copper and magnesium, to the 50% / 50% ingot, the casting was mixed and nine specimens were poured into the mold and a sample was taken for chemical analysis. This is presented in Table 10.
There is a proportional increase in the addition of copper to the melt (50% / 50% ingot), which was successful, representing 4.176% of the alloy. The next addition was made with the incorporation of 40 g of magnesium.
There was a slight contamination of impurities from the crucible wall, which resulted in an increase in zinc, with a value of 1.569% in the alloy.
Next, a new casting was made, an additional 30 g of copper and 80 g of magnesium were added. Due to the addition of magnesium, argon gas injection was used to control oxygen contact in the bath since magnesium is highly soluble when in contact with oxygen. After stabilization of the bath and homogenization of the alloy, the argon was turned off and the melt was poured back into the mold and heated at 350 ° C. With the addition of copper and magnesium, an improvement in uidity was noted and, as a result, the channels were completely lled. This left the specimens at the size determined by measuring of the mold channel. A new chemical analysis was performed with the samples resulting from the mixture provided in Table 1. These results are presented in Table 11: The percentages of copper and magnesium were 7% and 6.775% respectively. Magnesium did not reach the predicted percentage of 8% from Table 1 due to the degree of solubility and an increase in slag formation on the surface of the melt caused by magnesium oxidation. Copper behavior remained stable as in previous ows. The other elements remained practically the same in relation to the previous additions made.

Conclusion
Aluminum cans are a good choice for the collection and sale of recyclable materials because they are easy to collect and have a relatively high value. Of course, when it comes to recycling, impurities will always exist in the casting process, which will contribute to slag formation. Thus, researching casting methods or techniques that improve process performance is the rst challenge for researchers interested in the topic of metal recycling.
The process of casting recycled aluminum shows a wide possibility for reusing solid waste. In addition to providing income to support many families of waste pickers in urban centers, recycled aluminum can be used for various industrial applications.
The sustainability bias brings another important point when considering the recycling of materials, since the continued depletion of minerals from the earth's crust is a well-known fact. For this reason, this research is relevant. Recycling aluminum allows for the reuse of materials and reduces the need for underground mining.
One of the objectives of this research focused on the reuse of recycled materials. In addition, this work proposed a more appropriate destination for industrial waste, therefore offering possibilities for saving materials. However, it is important to improve the casting process of the melt ow in order to facilitate the extraction of specimens for several applications.
By conducting this research, casting recycled aluminum from beverage cans after the separation of the initial slag, proves to add great e ciency to the recycling process of this material. However, this is only possible when the aluminum is properly separated and used correctly, without di culties in the handling process. Therefore, casting recycled aluminum offers possibilities for other applications, simply by adapting matrices or molds to the product to be produced. There is a possibility to expand the methodologies and obtain new applications of aluminum casting, so that the use of clean technologies that promote greater sustainability can be advanced.
The addition of copper and magnesium to the molten aluminum for the ingot containing 50% recycled aluminum and 50% commercial aluminum has shown a great possibility for the casting of different materials with developed methodologies. This was demonstrated in this research through the production of a new alloy where 85% aluminum, 6.38% copper and 8.51% magnesium were obtained. This is presented in table 1.    Table 4 Analysis of the chemical composition of the aluminum can casting used by Verran and Kurzawa (2008).   Table 6 Experimental sequence of alloy formation of the 50% / 50% ingot.

Figure 2
Methodological sequence of the research steps during the casting process.

Figure 3
Manual placement of aluminum cans.

Figure 4
Slag removed from the melt.
Page 18/21 Mold made for pouring of the 3rd ingot Pouring process of molten aluminum into the mold Figure 8 Opening of the mold and removal of specimens from the 1st batch of samples from the 50% / 50% ingot experiment.