International Journal of Engineering & Technology IJET-IJENS Vol:15 No:04 43

Transcription

1 International Journal of Engineering & Technology IJET-IJENS Vol:15 No:04 43 Direct Recycling of Aluminium 6061 ChipThrough Cold Compression B.L.Chan *,M.A. Lajis Sustainable Manufacturing and Recycling Technology (SMART), Advanced Manufacturing and Materials Center (AMMC), UniversitiTun Hussein Onn Malaysia (UTHM), Parit Raja, BatuPahat, Johor, Malaysia *corresponding author: Abstract--Aluminium is globally used in many different ways, from beverages cans to a large aircraft. This is due to aluminium s remarkable mechanical properties as the same time having a low density. The high usage of aluminium in the everyday life, encourage higher production of aluminium where high energy consumption manufacturing process such as melting bauxite for primary material or melting recycled aluminium conventionally for secondary aluminium. So by directing recycling the aluminium chip through cold compression will reduce the energy consumption during the manufacturing process. In this process the aluminium chipwere compressed at maximum of 45 tons force with a set amount of holding time. The compressed specimens were then strengthening through sintering. Through sintering, the Ultimate tensile strength (UTS) of the specimen increased but at the same time micro-hardness and the density is sacrifice. On the other hand, the Elongation to failure (ETF) reduced due to the high compression force which exceeded the optimum. Further deformation process which involved shearing would be recommended to further improve the overall properties. Index Term-- aluminium chip Solid state recycling, Cold compression, INTRODUCTION Reycling of aluminium scrap has been widely practiced in many countries to reduce the wastage of natural resources (Gronostajski, J.Z. et al., 1997, Guley, V. et al., 2010, Misiolek W.Z. et al., 2012).The aluminium scarps are required to undergo the remelting process during the recycling process when conventional method has been implemented. However, due to the high temperature needed to completely remelt the aluminium scraps, there is a high consumption of energy with high operating cost (Gronostajski, J.Z. et al., 2000). Therefore, direct recycling or solid state recycling is introduced and able to recycle the aluminium scraps without undergoing the remelting process. So the usage of energy and the loss of material are reduced during the recycling process (Tekkaya, A.E. et al., 2009) Currently there are a few direct recycling techniques being developed, namely hot extrusion, powder metallurgy, hot forging and cold compression. Here, the focus will be in the uses of cold compression in direct recycling. Cold compression technique has not been researched much before in particularly on mechanical properties, as well as in the microstructure of the compressed sample. Hence, to further research on this technique both the data on mechanical properties will be invertrated. METHODOLOGY Pre-compression process Chips cleaning are a crucial process as oil, moisture and other oxides may be present in the chips. If these impurities were present in the chips, this may lead to problem Fig. 1. Overall methodology during sintering process which in turn results in strength loss (Samuel, 2003). So the chips were cleaned using ethanol in an ultrasonic bath. The cleaned chips were then oven dried at 60 C for one hour to remove any moisture in the chips during the cleaning process.

2 Ultimate Tensile Strength, UTS (MPa) Ultimate Tensile Strength, UTS (MPa) International Journal of Engineering & Technology IJET-IJENS Vol:15 No:04 44 Cold Compression Process Pepelnjak (2012) stated that the compression force of 300 kn has been proved to be insufficient as the compressed specimens experience low density as well as low integrity. So a higher compression force would be enforced to ensure higher density and higher integrity in the compressed sample. During the process of cold compression, the sample will be compressed 4 times instead of the traditional single layer compression which will allow a higher density on the compressed sample (Misiolek, 2012). Holding time which are rarely applied on cold compression can be found used in some research methodology will be research deeper with holding time of 1, 5 and 10 minutes. Post-compression process Through cold compression the compressed sample will have high density and high integrity but the quality of the bond between the chips would still remain as an issue due to lack of large shear deformation (Kuzman, 2012). By finding an alternative post-process, sintering which are used in powder metallurgy would strengthen the compressed powder. By applying the same principle on compressed chips higher strength as well as better bonding between chips would be obtain. The over view of the study is shown in figure 1. RESULTS AND DISCUSSION The compressed specimen with the lowest UTS is 2.77 MPa as shown in figure 2, where the specimen undergoes a compression of 45 tons with a holding time of 5 minutes and without sintering. On the other hand, the compressed specimen with the highest UTS is MPa which is more than 5 times higher than the lowest UTS of the compressed specimen is shown in figure 3. This specimen was compressed at a holding time of 1 minute and compression force of 35 tons with the highest sintering temperature of. From the graph, the UTS of the compressed specimens are directly proportional to the sintering temperature, where the increase in the sintering temperature will result in higher UTS. This may be due to the reduction of the porosity which enhances the strength of the compressed specimens. Fig. 2. Ultimate tensile strength for different sintering temperature at different holding time [F = 45.0 tons] Fig. 3. Ultimate tensile strength for different sintering temperature at different holding time [F = 35.0 tons] The highest value of ETF of the compressed specimen is only 3.98%, where the specimen was subjected to the lowest force of 35 tons and a holding time of one minute without sintering process. Whereas, the lowest ETF goes down to the specimen that was sintered at after compressed at 45 tons for ten minutes, which yielded the ETF of 1.23%. The ETF of the compressed specimens are inversely proportional to the compression force during the compression process.

3 Elongation to failure, ETF (mm) Elongation to failure, ETF (mm) International Journal of Engineering & Technology IJET-IJENS Vol:15 No:04 45 Though compression force maybe one of the key factor in improving the mechanical properties, but in this case the compression force bring a decreasing influence on the ETF as the compression force has go beyond the optimum at 650 MPa (Fogagnolo, J.B. et al., 2003) tons 40 tons 45 tons Fig. 4. Elongation to failure for different compression force at different holding time [No sintering] tons 40 tons 45 tons Fig. 5. Elongation to failure for different compression force at different holding time [T= ] The hardness of the specimen shows a different outcome compare to both the tensile and elongation to failure. From all the three graphs below, there is a same trend being shown where the specimen that do not undergo sintering having a higher micro-hardness and the specimen that undergoes sintering at and will have a comparative lower micro-hardness. On average the microhardness of specimen without sintering is roughly three times higher than the specimens that have been sintered. The highest value is HV where the specimen was not sintered as shown in figure 6. On the other hand, micro-hardness of HV is the lowest, where the specimen was sintered at. The sintering of the specimen will make the specimen brittle thus making the specimen vulnerable to compression load form a sharp object.

4 Density (g/m3) Hardness (HV) Hardness (HV) International Journal of Engineering & Technology IJET-IJENS Vol:15 No: Fig. 6. Micro-hardness for different sintering temperature at different holding time [F = 40.0 tons] Fig. 7. Micro-hardness for different sintering temperature at different holding time [F = 45.0 tons] Coming to the density of the specimen, the results shows that higher density specimens are found in figure 8, when the specimens were not sintered, where the highest density is 2.66 g/m 3. As for the lowest density is 26% lower than the highest density with a density of 2.11 g/m 3 where sintering process taken place as shown in figure 9. So the sintering process does not only have decreasing effect on the micro-hardness but the density as well Force (Tons) From these results, recycling aluminium chips through cold compression does not bring about good recycled specimens in term of mechanical properties as well as in physical properties. Where there is a lack of chip bonding, even after sintering process, as there is a lack of shear deformation on the chips. These results bring forth a more complete view on the reason behind the lacking of the bonding of chips. Fig. 8. Density for different sintering temperature at different compression force [T = 1.0 min]

5 Density (g/m3) International Journal of Engineering & Technology IJET-IJENS Vol:15 No: Force (Tons) Fig. 9. Density for different sintering temperature at different compression force [T = 10.0 mins] CONCLUSION In this study of the direct recycling aluminium 6061 chips through cold compression, the following is the concluded result: i. The compression force only brings positive effect on the mechanical properties till the optimum pressure of 650 MPa. Compression force that exceeds the optimum will no longer bring any benefits in term of the mechanical properties like the UTS, hardness and the density. But on the other hand, cause the ETF to decrease. So keeping the compression on the optimum is enough to bring the best influence. ii. While the UTS of the specimen increase, the microhardness will be sacrifices. As the sintering process is implemented, the micro-hardness of the specimen greatly decreases. As a result, the micro-hardness of the specimens without sintering was roughly three times higher than the specimens that were sintered. At the same time, the density experience slight decrease as sintering process was implemented. Though the density of the compressed specimen reaches 2.66 g/cm 3 which are 98.52% of the density of the reference specimen but this specimen did not undergo sintering, due to the fact that the minimum compression force of 35 tons exert enough pressure to keep the compressed specimen at high density. iii. The decrease of both the micro-hardness and density were due to the heat that may expand the specimen during sintering. As the structure of the compressed specimens were not structurally stabile due to the interlocking of the chips, expanding during heating in sintering process will break the interlocking that help to increase the hardness of the compressed specimen. As the interlocking breaks, there are gaps that increase the overall volume which causes the density of the compressed specimen to reduce. iv. Overall, the specimens mechanical properties are still lacking comparing to the casted aluminium, where the specimens required to undergoes further deformation which may improve the bond of the chips. ACKNOWLEDGEMENT This research was supported by Malaysian Technical University (MTUN) and Fundamental Research Grants under Ministry of Education, Malaysia. Authors would like also to thank to the Sustainable Manufacturing and Recycling Technology (SMART) research cluster, Advanced Manufacturing and Materials Center (AMMC), UniversitiTun Hussein Onn (UTHM) for providing the facilities. REFERENCES [1] Fogagnolo, J. B., Ruiz-Navas, E. M., Simà 3 n, M. A. & Martinez, M. A. (2003). Recycling of aluminium alloy and aluminium matrix composite chips by pressing and hot extrusion. Journal of Materials Processing Technology [2] Gronostajski, J. Z., Kaczmar, J. W., Marciniak, H. &Matuszak, A. (1997). Direct recycling of aluminium chips into extruded products. Journal of Materials Processing Technology [3] Gronostajski, J., Marciniak, H. &Matuszak, A. (2000). New methods of aluminium and aluminium-alloy chips recycling. Journal of Materials Processing Technology, 106(1â 3), [4] Güley, V., Ben Khalifa, N. &Tekkaya, A. (2010). Direct recycling of 1050 aluminum alloy scrap material mixed with 6060 aluminum alloy chips by hot extrusion. International Journal of Material Forming, 3(0), Springer Paris [5] Kuzman, K., Kačmarčik, I., Pepelnjak, T., Plancak, M., &Vilotić, D. (2012). Experimental consolidation of aluminium chips by cold compression. Journal of Production Engineering, 15(2), [6] Misiolek, W. Z., Haase, M., Khalifa, N. B., Tekkaya, A. E. &Kleiner, M. (2012). High quality extrudates from aluminum chips by new billet compaction and deformation routes. CIRP Annals - Manufacturing Technology, 61(1), [7] Pepelnjak T., Kuzman K., Kačmarčik I., Plančak M.: Recycling of AlMgSi1 aluminium chips by cold compression, Metalurgija, 51(2012)4, pp , ISSN/ISBN: ISSN [8] Samuel, M. (2003). Reinforcement of recycled aluminum-alloy scrap with Saffil ceramic fibers. Journal of Materials Processing Technology, 142(2), [9] Tekkaya, A. E., Schikorra, M., Becker, D., Biermann, D., Hammer, N. & Pantke, K. (2009). Hot profile extrusion of AA aluminum chips. Journal of Materials Processing Technology, 209(7),