In the last few years, there is a demand for developing new technologies in order to increase scrap reuse potential and CO
2
emission savings. In this paper, aluminum was recycled from chips obtained ...by machining without any remelting in order to reduce environmental pollution and to increase material yield during the process. This process is called solid-state recycling (SSR) or direct recycling. SSR process consists of chips cleaning, cold pre-compaction, and hot direct extrusion followed by equal channel angular pressing (ECAP) at different temperatures. Influence of direct extrusion temperature, ECAP temperature, and number of ECAP passes on electrical conductivity and microhardness of the recycled EN AW 6082 aluminum chips was investigated. Microhardness and electrical conductivity of the recycled samples were comparable with commercially produced EN AW 6082. Experiments were planned utilizing design of experiments approach. Both adaptive neuro-fuzzy interference system (ANFIS) and regression models were developed and compared to describe the influence of input SSR process parameters on electrical conductivity and microhardness. Density and metallographic analysis of the recycled samples were also performed.
In the present study, aluminium AA-6061 alloy turning chips recycled using solid-state recycling technique through cold compaction followed by hot extrusion. The effect of the extrusion ratio (ER) ...and extrusion temperature (ET) on the microstructure evolution, the physical properties and the mechanical properties of the produced samples were studied. Moreover, the results were compared with those of the as-received samples extruded under the same conditions (reference samples extruded under ER = 5.2 and different ET = 350, 450 and 500 °C). Approximately dense samples with reasonable tensile strength, elongation, and microhardness were obtained. The tensile properties (strength and elongation) of recycled samples increased with the increase of the ER and ET those improve the bonding between chips. The chip samples processed under ER of 12.8 and ET of 500 °C have superior mechanical properties compared to the reference samples. The fracture surfaces of the recycled samples consisted of a combination of micro-cracks and equiaxed dimples according to the degree of the bonding of the chips.
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.
► Contrast material is used to visualize metal flow in screw extrusion of aluminium. ► Frictional conditions and main paths of material flow are determined. ► The interaction and mixing between ...granulate is shown. ► An explanatory model on the extrusion pressure generating mechanism is presented.
Screw extrusion is a new continuous solid state processing method for aluminium. In this process, small pieces of aluminium are continuously inserted into a container wherein a rotating screw pushes the material forward. The material is heated, consolidated and extruded through a die in front of the end of the screw in one single continuous process. Understanding the material flow and the pressure generating mechanism is vital for optimizing screw, container and die designs, thereby increasing capacity, material quality and process stability. Full scale experiments using a prototype extruder were chosen as the means of investigation. In this paper, it is reported on the development of a novel contrast material technique to visualize material flow in the screw channels and the extrusion chamber. Extrusion of Ø 10mm aluminium profiles was performed using both single and double flight screws. The experimental technique provided a means for evaluating the frictional conditions between the aluminium and the surface of the extruder. Different feeding schemes were used to identify regions of high material flow rate together with dead metal zones in the screw channels and in the extrusion chamber. It is demonstrated how newly fed material interacts with and displaces material already present and how the screw pushes material into the extrusion chamber. The instantaneous extrusion velocity was measured and significant variations were detected for all feed rates. An explanatory model of the extrusion pressure generating mechanism in the extrusion chamber and the screw channel is presented linking the material flow and the consolidation process to the extrusion velocity variations.
The production of metal matrix composites (MMCs) through recycled materials is a cost-saving process. However, the improvement of the mechanical and physical properties is another challenge to be ...concerned. In this study, recycled aluminium 6061 (AA6061) chips reinforced with different volumetric fractions of boron carbide (B4C) were produced through hot equal channel angular processing (ECAP). Response surface methodology (RSM) was carried out to investigate the dependent response (compressive strength) with independent parameters such as different volumetric fractions (5-15%) of added contents of B4C and preheating temperature (450 – 550°C). Also, the number of passes were examined to check the effect on the mechanical and physical properties of the developed recycled AA6061/B4C composite. The results show that maximum compressive strength and hardness of recycled AA6061/B4C were 59.2 MPa and 69 HV respectively at 5% of B4C contents. Likewise, the density and number of pores increased, which were confirmed through scanning electron microscope (SEM) and atomic force microscopes (AFM) analysis. However, the number of passes enhanced the mechanical and physical properties of the recycled AA6061/B4C composite. Therefore, the maximum compressive strength and hardness achieved were 158 MPa and 74.95 HV for the 4th pass. Moreover, the physical properties of recycled AA6061/B4C composite become denser of 2.62 g/cm3 at the 1st pass and 2.67 g/cm3 for the 4th pass. Thus, it can be concluded that the B4C volumetric fraction and number of passes have a significant effect on recycled AA6061 chips.
Enormous amount of scrap is generated on the shopfloor during manufacturing. Energy needed to melt increasing quantities of scrap will be ever increasing, and so will be the loss of metal during ...melting. Hence, conversion of scrap directly into marketable products by solid state processing methods is economical due to a lower energy requirement and a greater yield compared to the melting route. This makes the process more environmentally friendly. However, not all materials can be recycled in a solid state, with equal ease. One therefore needs to quantitatively assess the recyclability of a given kind of scrap. In the present work, a procedure to assess the recyclability of finely divided ferrous metallic scrap generated on the shopfloor is demonstrated. Recyclability includes material and the process used for recycling. For instance, a given material might be more recyclable using one process compared to the other. In the present study, the potential of powder technology (powder metallurgy (PM) and metal injection molding (MIM) based processes are compared for solid-state conversion of scrap directly into usable products. Grinding sludge collected in the shopfloor was pulverized and used as raw material. Properties of sintered parts were found to be significantly better due to in-situ reduction and densification during sintering. A quantitative measure of recyclability, namely, the Recyclability Index (RI) was defined to compare the manufacturability of different products. Recycled ferrous parts manufactured by PM route are found to have a greater RI (superior recyclability) than those manufactured by the MIM route. Complex reduction and sintering mechanisms in MIM parts, particularly, the kinetics of diffusion and volumetric shrinkage, limit suitability of MIM for recycling. In contrast, few industrial parts were developed and manufactured by conventional PM based approach to demonstrate the suitability of this novel recycling process especially for manufacture of porous parts.
The direct production of aluminum from bauxite ores is known to be a very energetic-intensive operation compared to other metallurgical processes. Due to energy issues and the rapid increase in ...aluminum demand, new kinds of aluminum production processes are required. Aluminum waste recycling, which has an advantage of lowering the cost of electric power consumption, is considered to be an alternative route for material manufacturing. In this work, the way of reusing aluminum EN-AC 44000 alloy scraps by hot extrusion was presented. Metal chips of different sizes and morphology were cold compacted into billet form and then hot extruded. Mechanical properties investigations combined with microstructure observations were performed. Mechanical anisotropy behavior of material was evaluated on the base of tensile test experiments performed on samples machined at 0°, 45°, and 90°, respectively, to the extrusion direction. It was found that the initial size of the chips has an influence on the mechanical properties of the received profiles. Samples produced from fine chips revealed higher tensile strength in comparison to larger chips, which can be attributed to a refined microstructure containing fine, hard Si particles and Fe-rich intermetallic phases. Finally, it was found that anisotropic behavior of chip-based profiles is similar to conventionally cast and extruded materials which prove good bonding quality between chips.
A method for recycling AZ91D magnesium alloy chips by solid-state recycling was studied. The experiments were carried out adopting the cold-press pressure and hot extrusion. The results indicate that ...recycled specimens of AZ91D magnesium alloy present better mechanical properties and consist of fine grains due to dynamic recrystallization. The mechanisms of dynamic recrystallization depend on plastic deformation process and change with the deformation temperature. At 300-350 °C, the deformation mechanisms are associated with the operation of basal slip and twinning, and the “necklace” structures are formed. At 350-400 °C, the cross slip results in the formation of new grains and grain refinement. At above 400 °C, the dynamic recrystallization mechanisms are controlled by dislocation climb, and recrystallized grains are homogeneous. The tensile strength of recycled specimens increases with the increase of the strain rate. When the strain rate is overhigh, the cracks and fractures in the surface appear and affect the tensile strength of recycled specimens.
AZ31B magnesium alloy chips of different size were recycled by hot extruding. Mechanical properties and microstructure of the recycled specimens and reference specimen were investigated. Amounts of ...oxide in recycled materials were estimated. Almost all the recycled specimens exhibit higher strength than reference specimens, this is mainly attributed to grain refinement strengthening whereas particle-dispersion strengthening has few effect. The strength of recycled specimen increases with increasing of total surface area of chips because of different grain size. Recycled specimens show inferior ductility than reference specimens and recycled specimens with medium surface area of chips possess highest elongation. Grain size, oxide amount and density of billet have an effect on the elongation of recycled materials.
PDF
