Recycling of Aluminum Scrap by Severe Plastic Deformation

Abstract

The production of primary aluminum is an energy costly process. With the global warming being of concern, the secondary aluminum stream is becoming an even more important component of aluminum production and is attractive due to its economic and environmental benefits. Recycling of aluminum by new solid state recycling techniques instead of conventional remelting and subsequent refining processing can result in significant energy savings. Severe Plastic Deformation (SPD) techniques have been applied for consolidating nano particles into fully dense materials with good mechanical properties. However, solid state recycling of scraps by SPD is only in the beginning. In the present study, degreasing of aluminum chips from the machine workshop was investigated by a thermal method and chemical treatment. Thereafter, the decoated chips were recycled by Cyclic Extrusion Compression (CEC) at deformation temperatures between 400 and 500 °C. The microstructure and mechanical properties of the recycled aluminum scrap processed by SPD were subsequently investigated. The results show that SPD technology provides a promising alternative for recycling of aluminum scrap. Thermal degreasing of aluminum scrap resulted in more oxidization of aluminum scrap particles. Visible interfaces between chips were observed even at a low magnification.

Review of measures for improved energy efficiency in production-related processes in the aluminium industry – From electrolysis to recycling

“…Recycling through hot extrusion is based on the compaction of (small) aluminium scrap into billets followed by conventional hot extrusion [69][70][71][72]. To ensure proper bonding between the scrap pieces, contact between pure aluminium surfaces must be achieved through the breaking of the oxide layers covering the scrap pieces [69,71]. This is accomplished by affecting the scrap with plastic deformation and compressive stresses during the extrusion process [69].…”

“…Plastic strain can be created by pressing the chips through a special die with channels intersected at an angle after the actual extrusion [73], as shown in Figure 11. One example is the extrusion process called Cyclic Extrusion Compression, which operates at 500 °C with five passes through the die [71]. This process has been shown to provide enough plastic deformation to consolidate the scrap particles [71].…”

“…One example is the extrusion process called Cyclic Extrusion Compression, which operates at 500 °C with five passes through the die [71]. This process has been shown to provide enough plastic deformation to consolidate the scrap particles [71]. Another issue which must be dealt with is contaminants, which require additional processes [70][71][72].…”

“…Compared to traditional remelting of scrap, recovery through hot extrusion has a lower energy usage as well as a higher recovery efficiency [70][71][72]. This means that both the production costs and solid waste generation are reduced [70].…”

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

“…A finer grain size increases the strength and the fracture toughness of the material [11]. SPD processes commonly used for SSR are: Equal channel angular pressing (ECAP) [12,13], cyclic extrusion compression (CEC) [14], and high pressure torsion (HPT) [15]. Lately, new and promising methods for SSR are arising such as friction stir extrusion (FSE) [16] and friction stir consolidation (FSC) [17].…”