Statistical Analysis of the Combined ECAP and Heat Treatment for Recycling Aluminum Chips Without Remelting

The main aim of this paper is to present an environmentally friendly method for aluminum recycling. Development of new recycling technologies in order to increase scrap reuse potential and CO2 emission savings are of the main importance for aluminum circular economy. In this paper, aluminum chips waste was recycled without any remelting phase in order to increase energy and material savings. The presented process is usually called solid state recycling or direct recycling. Solid state recycling process consists of chips cleaning, cold pre-compaction and hot direct extrusion followed by a combination of equal channel angular pressing (ECAP) and heat treatment. Influence of holding time during solid solution treatment and both artificial aging time and temperature on mechanical properties of the recycled EN AW 6082 aluminum chips were investigated. A comprehensive number of the experiments were performed utilizing design of experiments approach and response surface methodology. Regression models were developed for describe the influence of heat treatment parameters for presented solid state recycling process on mechanical properties of the recycled samples. Utilizing novel procedure high quality recycled samples were obtained with mechanical properties comparable with commercially produced EN AW 6082 aluminum alloy in T6 temper condition. Metallographic analysis of the recycled samples was also performed

Enhanced Mechanical Properties of Aluminium Alloy EN AW 6082 Recycled without Remelting

Main aim of this research was to investigate unconventional method for aluminium recycling. Recycling process presented in this research was performed in solid state and therefore is called solid state recycling (SSR) or direct recycling. Main aim of direct recycling approach is to reduce greenhouse gasses emission compared with primary aluminium production and conventional recycling. Other advantages are higher scrap material yield during recycling and energy savings. In this paper, SSR process consisted of aluminium chips hot extrusion and afterwards severe plastic deformation process at room and elevated temperatures. Mechanical properties of the solid state recycled samples obtained by presented process were comparable with samples obtained by conventional manufacturing. Furthermore, it was shown that additional plastic deformation after hot extrusion significantly improved mechanical properties of the recycled samples compared with those recycled only by hot extrusion. Analysis of both microstructure and density analysis was also performed

ANALYSIS OF PRODUCTION METHOD AND STABILIZING AGENT ON STRUCTURE OF ALUMINUM METAL FOAMS

Aluminum alloy foams are a form of porous metal whose structure resembles the shape of natural materials such as coral, bone, sponge, etc. Due to their structure, these materials retain good mechanical properties of the base material while being significantly lighter than non-porous metal. Metal foams can be used as energy and vibration absorbers, heat exchangers, insulators, and filters. The main disadvantage of this type of material is its high production cost. To reduce production costs, aluminum alloy chips are used as base material. Foams are made of A360 and AA 7075 aluminum alloys. To produce a porous structure, CaCO3 is used as a foaming agent while Zn and CaO were added as stabilizing agents. The main goal of the paper was to investigate the difference in the shape of pores and relative density after foaming with different stabilizing agents

Modelling and optimization of aluminum waste recycling process in solid state

Tema ove disertacije je istraživanje procesa recikliranja aluminijskog otpada u čvrstom agregatnom stanju. Taj pristup u ekonomskom i ekološkom smislu je povoljniji od konvencionalnog recikliranja zbog manjeg utroška energije, ispuštanja stakleničkih plinova u atmosferu i većeg stupnja iskorištenja materijala. U ovoj disertaciji, pisanoj prema Skandinavskom modelu, može se dobiti cjelovita slika o proizvodnji kvalitetnih uzoraka recikliranih bez pretaljivanja metala. U većem dijelu istraživanja korištena je metodologija planiranja pokusa s ciljem dobivanja matematičkih modela koji služe kao značajan, postojan i nepristran alat u opisivanju inovativnog procesa. U prvom istraživanju proučavano je recikliranje procesom istosmjernog istiskivanja u toplom stanju te je zaključeno da je temperatura istiskivanja najutjecajniji parametar na kvalitetu recikliranih uzoraka. U sljedeća dva istraživanja, u kombinaciji s istiskivanjem, korišten je proces intenzivne plastične deformacije što je dovelo do značajnog poboljšanja kvalitete recikliranih uzoraka. U četvrtom istraživanju proučavan je utjecaj toplinske obrade u kombinaciji s procesom intenzivne plastične deformacije. Time su dobiveni kvalitetni reciklirani uzorci što su pokazala ispitivanja mehaničkih i fizikalnih svojstava, kao i metalografska analiza. U finalnom istraživanju, pokazano je da su korozijska svojstva uzoraka recikliranih u čvrstom stanju bolja, dok je životni vijek pod dinamičkim opterećenjem sličan u odnosu na konvencionalno proizvedene uzorke.The topic of this dissertation is to investigate the process of recycling aluminium waste in solid state. That approach in both economic and environmental terms is more appropriate than conventional recycling process due to the reduced energy consumption, greenhouse gasses emissions and higher material yield. In this doctoral dissertation, written according to the Scandinavian model, can be given a complete picture of the production of quality samples recycled without metal remelting. In most part of the research it was used design of experiments methodology with aim to derive mathematical models which should serve as a significant, robust and impartial tool in describing an innovative process. In first research solid state recycling using hot direct extrusion was investigated with conclusion that extrusion temperature was most influence parameter on recycled samples quality. In next two researches in combination with direct hot extrusion, severe plastic deformation process was used leading to significant increase of the recycled samples quality. In fourth research, influence of the heat treatment in combination with severe plastic deformation process was investigated thus producing quality recycled samples which was confirmed with mechanical and physical properties determination as well as metallographic analysis. In the final research, it was showed that corrosion properties of the samples recycled in solid state are better, while fatigue life was similar to that of conventionally produced samples

Modelling and optimization of aluminum waste recycling process in solid state

Tema ove disertacije je istraživanje procesa recikliranja aluminijskog otpada u čvrstom agregatnom stanju. Taj pristup u ekonomskom i ekološkom smislu je povoljniji od konvencionalnog recikliranja zbog manjeg utroška energije, ispuštanja stakleničkih plinova u atmosferu i većeg stupnja iskorištenja materijala. U ovoj disertaciji, pisanoj prema Skandinavskom modelu, može se dobiti cjelovita slika o proizvodnji kvalitetnih uzoraka recikliranih bez pretaljivanja metala. U većem dijelu istraživanja korištena je metodologija planiranja pokusa s ciljem dobivanja matematičkih modela koji služe kao značajan, postojan i nepristran alat u opisivanju inovativnog procesa. U prvom istraživanju proučavano je recikliranje procesom istosmjernog istiskivanja u toplom stanju te je zaključeno da je temperatura istiskivanja najutjecajniji parametar na kvalitetu recikliranih uzoraka. U sljedeća dva istraživanja, u kombinaciji s istiskivanjem, korišten je proces intenzivne plastične deformacije što je dovelo do značajnog poboljšanja kvalitete recikliranih uzoraka. U četvrtom istraživanju proučavan je utjecaj toplinske obrade u kombinaciji s procesom intenzivne plastične deformacije. Time su dobiveni kvalitetni reciklirani uzorci što su pokazala ispitivanja mehaničkih i fizikalnih svojstava, kao i metalografska analiza. U finalnom istraživanju, pokazano je da su korozijska svojstva uzoraka recikliranih u čvrstom stanju bolja, dok je životni vijek pod dinamičkim opterećenjem sličan u odnosu na konvencionalno proizvedene uzorke.The topic of this dissertation is to investigate the process of recycling aluminium waste in solid state. That approach in both economic and environmental terms is more appropriate than conventional recycling process due to the reduced energy consumption, greenhouse gasses emissions and higher material yield. In this doctoral dissertation, written according to the Scandinavian model, can be given a complete picture of the production of quality samples recycled without metal remelting. In most part of the research it was used design of experiments methodology with aim to derive mathematical models which should serve as a significant, robust and impartial tool in describing an innovative process. In first research solid state recycling using hot direct extrusion was investigated with conclusion that extrusion temperature was most influence parameter on recycled samples quality. In next two researches in combination with direct hot extrusion, severe plastic deformation process was used leading to significant increase of the recycled samples quality. In fourth research, influence of the heat treatment in combination with severe plastic deformation process was investigated thus producing quality recycled samples which was confirmed with mechanical and physical properties determination as well as metallographic analysis. In the final research, it was showed that corrosion properties of the samples recycled in solid state are better, while fatigue life was similar to that of conventionally produced samples

Production of Closed-Cell Foams Out of Aluminum Chip Waste: Mathematical Modeling and Optimization

The main aim of this research is to mathematically describe the influence of the processing parameters of metal foam production from machining chip waste. Using this method, metal foams were produced without a remelting step, which should be both economically and environmentally effective. Firstly, expensive metal powders were replaced with waste in the form of machining chips. Secondly, machining chip waste was recycled without any significant material losses, which usually occurs during conventional recycling (using the melting process). To describe the innovative process and to relate metal foam properties to foaming temperature, the blowing agent weight percentage, and foam density (controlled by foaming height), response surface methodology, and the design of experiments were used. The quality of the produced metal foams was evaluated by determination of density, yield strength, compression strength, plateau stress, energy absorption, pore perimeter, and pore inhomogeneity for specimens obtained following the experimental plan. It was proven that pore inhomogeneity increased in the range from 1.41 to 4.81 mm with a higher temperature and the addition of a foaming agent. However, higher energy absorption and yield strength were obtained with a higher temperature but a lower percentage of TiH2. Despite the production from machining chips, pores were homogenous without significant cracks. These kinds of metal foams are comparable to commercial foams made of metal powders

Production of Closed-Cell Foams Out of Aluminum Chip Waste: Mathematical Modeling and Optimization

The main aim of this research is to mathematically describe the influence of the processing parameters of metal foam production from machining chip waste. Using this method, metal foams were produced without a remelting step, which should be both economically and environmentally effective. Firstly, expensive metal powders were replaced with waste in the form of machining chips. Secondly, machining chip waste was recycled without any significant material losses, which usually occurs during conventional recycling (using the melting process). To describe the innovative process and to relate metal foam properties to foaming temperature, the blowing agent weight percentage, and foam density (controlled by foaming height), response surface methodology, and the design of experiments were used. The quality of the produced metal foams was evaluated by determination of density, yield strength, compression strength, plateau stress, energy absorption, pore perimeter, and pore inhomogeneity for specimens obtained following the experimental plan. It was proven that pore inhomogeneity increased in the range from 1.41 to 4.81 mm with a higher temperature and the addition of a foaming agent. However, higher energy absorption and yield strength were obtained with a higher temperature but a lower percentage of TiH2. Despite the production from machining chips, pores were homogenous without significant cracks. These kinds of metal foams are comparable to commercial foams made of metal powders

Corrosion Behavior of Stainless Steel in Seawater in the Presence of Sulfide

The effect of temperature (from 288 to 308 K) and concentration of sulfide ions (up to 40 ppm) on the corrosion behavior of AISI 304L and AISI 316L stainless steels in seawater was studied with measurements of open-circuit potential, linear and potentiodynamic polarization, and electrochemical impedance spectroscopy. An increase in temperature and pollutant concentration negatively affects the corrosion stability of stainless steels at the open circuit (the resistance, compactness, and thickness of the surface layer decrease and the corrosion current increases), in the passive region (the passivation current increases, the depassivation potential decreases, and the passive potential region narrows), and in the transpassive potential region (the rate of metal dissolution increases). The occurrence of pitting corrosion on the surface of the samples was confirmed with optical microscopy and a non-contact 3D profilometer. A few large pits (depth 80–100 μm and width 100 μm) were formed on the surface of AISI 304L steel, while several smaller pits (depth 40–50 μm and width 50 μm) were formed on the surface of AISI 316L steel. With increasing temperature and sulfide ion concentration, the width, depth, and density of the pits increased on both steel samples. In the studied temperature and concentration range of sulfide ions, the AISI 316L steels exhibited higher corrosion resistance. Overall, the influence of sulfide ions on steel corrosion was more pronounced than the influence of temperature