EFFECT OF EXTRUSION RATIO OF RECYCLING ALUMINIUM AA6061 CHIPS BY THE HOT EXTRUSION
PROCESS
Syaiful Nizam Ab Rahim1*, Mohd Zaniel Mahadzir1, Nik Ahmad Faris Nik Abdullah1, Mohd Amri Lajis2
1Department of Mechanical Engineering, Politeknik Sultan Abdul Halim Mu’adzam Shah (POLIMAS), Bandar Darulaman, 06000 Jitra, Kedah, Malaysia
2Sustainable Manufacturing and Recycling Technology, Advanced Manufacturing and Materials Center (SMART-AMMC), Universiti Tun Hussein Onn Malaysia, 86400 Parit Raja, Batu Pahat, Johor, Malaysia
*Corresponding Author: [email protected]
Accepted: 1 December 2019 | Published: 30 December 2019
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Abstract: This research investigated the effects of hot extrusion parameters in direct recycling aluminium alloy chips (AA6061) focusing on automotive and light tools application. The experiments have been carried out using 250T hot extrusion machine. Due to the substantially increased demands of aluminium, it is required for improvement of its mechanical properties by using a suitable approach combination of recycling aluminium chips. The extrusion process was also affected by the strength of the material, which is a combination of optimum extrusion ratio, preheat temperature and preheat time. The most principle parameter of processing wrought alloys is temperature and extrusion ratio. Tensile test results showed that, material extruded at 550°C exhibited higher mechanical properties, compared to that extruded at 450°C at ER 12 and ER 6. The result shown for UTS as- received is 328 MPa, ASM Theory AA6061-T4 is 240 MPa and best recycling chips providing UTS is 189 MPa (before the heat treatment process). The tensile of the chip will increase to tensile as-received after the heat treatment process. Hot extrusion parameter showed that temperature gave more significant effect in responses rather than preheating time hence the higher Extrusion Ratio (ER) give a better results on Ultimate Tensile Strenght .
Keywords: Sustainable direct recycling, Metal recycling, Hot extrusion, Aluminum recycling _________________________________________________________________________
1. Introduction
Extrusion is defined as the process of shaping material, such as aluminum, by forcing it to flow through a shaped opening in a die. Aluminum extrusion is a technique used to transform aluminum alloy into objects with a definitive cross-sectional profile for a wide range of uses.
The extrusion process capitalizes on the built-in advantages in aluminium and increases their use and applications. Repeating the experiment to achieve desired optimized extrusion process condition will be expensive and time-consuming (Misiolek W. Z. et.al., 2012). For improving recyclability of aluminium there are some areas should be focused for instance ram speed (Vr), preheat temperature (T) and preheat time (t) in the recycling of aluminium.
Yet, research for modelling of hot extrusion parameter process not really established especially for optimization method. Extrusion ratio is another parameter that was considered which is influenced by using a higher or lower ratio for optimizing the extruded aluminium (Gattmah, J.et.al., 2017). By using though the flat-face die, an ER of lower than 4 did not
guarantee sufficient chip bonding. While at the higher extrusion ratio (ER > 10), the extruded profiles were found to gain superior strength and ductility (Chiba at el., 2015). It is also stated that at high extrusion ratio, excessive strain, high compressive pressure and high shear forces can be imposed on the extruded profiles to successfully break the oxide layers surrounding the chip surfaces.
2. Literature Review
Extrusion is commonly classified as a hot-working process. Hot working is defined as deformation under conditions of temperature and strain rate such that recovery processes take place simultaneously with deformation. Temperature is one of the most important parameters in extrusion (Tekkaya et. al., 2012). The flow stress is reduced if the temperature is increased and deformation is, therefore, easier, but at the same time, the maximum extrusion speed is reduced because localized temperature can lead to the incipient melting temperature. The changes during extrusion depend on the billet temperature, the heat transfer from the billet to the container, and the heat developed by deformation and friction. Rahim S.N. et al., (2016) showed the major extrusion parameters include the die design representing redundant work (additional material shearing) and friction forces within the die, the extrusion ratio R, ram speed, and extrusion temperature. With the application of computers in both the design and manufacturing of extrusion dies, it has been possible to use very small bearing lengths. The scope is to optimize bearing lengths for each shape with respect to the alloy to be extruded and the life of the die. Through research, new alloys or derivatives of existing alloys with improved extrudability and higher mechanical properties continue to be developed. The future task in billet making is to make more purity billets through continuously developing degassing, grain refining and filtration systems. The result is promising in terms of energy savings and production of the highest quality engineered aluminium profiles. It shown that multi-layer compaction technique allows preparation of chip-based billets with higher density. The 7.5% higher billet density achieved by multi-layer compaction with four layers in comparison to single-layer compaction did not change the mechanical properties of the profiles extruded through the flat-face die with R = 34. Furthermore that higher ram speed or extrusion ratio for the ECAP die led to a slight decrease of strength and ductility for the extrudates due to higher deformation temperature (Haase, M. et.al., 2015). On the other hand, using the higher extrusion ratio seems to produce a good consolidation for both kinds of pressed chips. The ultimate tensile strength (UTS) of the extruded materials obtained from the cold and hot pressed chips extruded with a 25:1 extrusion ratio. Figure 1 shown types of Extrusion Ratio (ER).
Figure 1 : Illustration of extrusion die ER 12 and ER 6
3. Methodology
Software Design Expert 8 will be used to perform Response Surface Method (RSM). The experimental design of the research work consisted of two phases. During the first phase, experimentation is performed in the full factorial design where three main parameters that are preheat time, preheat temperature and extrusion ratio was applied. For the second phase, the experimental runs were designed based on the Miscellaneous. These models can be obtained using DOE, followed by analysis of variance (ANOVA) and regression analysis (RA) (Rahim S. N. et.al., 2017). The first step to a successful experimental planning is to choose a range of studied process parameters and literature review. Personal experience is also a helping hand in this issue. It was decided to vary the process parameters, namely, constant ram speed, preheating time and extrusion temperature in the range from 1 mm/s, 1 to 3 hours, and temperature between 450°C to 550°C, respectively. The DOE was realized using the miscellaneous RSM. In the experimental research, Miscellaneous is very often used because it offers optimization possibility and reduction of the number of experiments (Kamaruzaman et.al., 2016). Two factorial miscellaneous experiments demand eight (8) experiments (each factor on 3 levels) and 3 central experiments, which makes a total of 11 experiments (N= k2+
k + cp, where k is the number of factors and cp is the number of central point replications).
Software package Design-Expert was used to generate 11 experimental points.
Table 1 : Comparison on UTS and EtF (ER12 & ER6)
Std Run Run
No
Preheat Temp. (° C)
Preheat Time (h)
Ultimate Tensile Strength (MPa)
Elongation to failure (%)
ER12 ER6 ER12 ER6
1 3 450 1 146.06 141.16 22.26 14.49
2 2 500 1 169.58 138.67 25.05 11.36
3 10 550 1 169.74 160.51 16.57 9.07
4 1 450 2 159.93 136.51 19.61 11.51
5 5 500 2 171.46 159.87 29.37 19.57
6 4 550 2 185.45 165.51 17.46 11.97
CP 7 500 2 150.58 132.44 22.56 12.69
CP 11 500 2 160.25 140.69 21.88 12.02
7 9 450 3 163.5 167.82 24.6 17.39
8 8 500 3 175.72 162.09 28.54 20.63
9 6 550 3 189.2 170.85 18.31 9.07
The aluminum chips of medium type were compacted to billets inside a thick-walled steel tube with an inner diameter of 30 mm. Table 1 shows the result of tensile. The relationship between maximum stresses in relation to temperature for both tested materials is shown in Figure 2. It can be seen that increasing maximum stress leads to the enhancement of preheat temperature, which is a typical behavior of the direct extrusion process. Consequently, the higher preheat temperature is applied the higher deformation is induced, which in turn results in increasing maximum stress. Furthermore, the 7.5% higher billet density achieved by multi- layer compaction with four layers in comparison to single-layer compaction did not change the mechanical properties of the profiles extruded through the flat-face die with R=6.
Furthermore, the bonding between individual chips is weak as it will be seen from the microstructure investigation. However, this value of average density is higher as compared
with the work of other researchers; especially when the compaction process is conducted at room temperature. Preheating duration times were influenced a better homogeneity of the billet structure made a better consolidation during extrusion processes. At high extrusion temperature, good diffusion bonds and very low porosity of extruded composites could be obtained (Rahim et al., 2017). The billet temperature is approximately the same as the container temperature. Effect of chip type of the mechanical properties the profiles extruded almost the same strength with a slightly higher ductility in case of medium chip. A solid state recycling process utilizing compression and extrusion at room or moderate temperature can result in significant energy savings.
The results revealed that the effects of extrusion preheat time and preheat temperatures were predominant only at high temperatures. Tensile test results of the extrusion of a 10 x 6 mm flat face die at a constant billet temperature of 450°C and profile exiting speeds of 1 mm/s is given. The best parameters are shown in preheat temperature within 3 hours and the heating temperature is 550°C to 189.20 MPa, which is 73.15% closed to the as-received. While the lowest parameter is shown in a state of preheat time within 2 hours and the temperature is 450°C to 146.06 MPa, which is 64.31% less than the theoretical value. The results on the effect of preheat temperature clearly give the significant impact to the extrusion process by proving that at constant ram speed, value of UTS surged up to 146.06-189.20 MPa by increasing the preheat temperature from 450°C to 550°C and preheat time from 1 hour to 3 hours. The preheat time and preheat temperature must be well controlled, because over condition or insufficient may not cause the coarsening, spheroidization and decreasing precipitate (Den Bakker A.J. et al., 2014). The welding of the aluminium chips consolidates much better at higher temperatures.
Figure 2 : Graph comparison Extrusion Ratio (ER) on Ultimate Tensile Strenght and Elongation
Figure 2 shows, the low elongation occurred in a preheat time of 1 hour, which is 9.07% to 14.49% of the as-received elongation using the extrusion ratio 6. Meanwhile, medium elongation occurred at a temperature of 500°C preheated 2 hours by 11.51% to 19.57% of the as-received value of 16% elongation. Prolongation of the best results occurred in the preheat time of 3 hours, which contributed 11.36% to 20.36% over the average of 16% of the original value. The ductility of the profiles extruded with the preheat time of 3 hours and at temperature of 550°C, which is 55.07% higher than the ductility of the profiles temperature 450°C that extruded through the flat-face die. The ductility of the profiles extruded at an hour is lower elongation at 9.07%. The ductility of the profiles extruded from chips at 3 hours and 450°C is even higher than the profiles extruded from as-received. According to Shokuhfar A.
et al., (2014), the quality of the product is controlled by extrusion factor, die design, extrusion ratio, billet temperature, lubrication for hot extrusion case and extrusion speed. The quality of the chip-based finish parts strongly depends on the bonding quality between the individual chips. The minimum result occurred at preheat time of 1 hour at a temperature of 450˚C with a low extrusion ratio of 6, elongation is 9.07 % respectively. The experimental results showed the deformation and fracture mechanisms at elevated temperature for the recycled specimen were different from those of the as-received specimen, although the difference in grain size was minor between the recycled specimen and the as-received specimen (Rahim S.N. et.al., 2016). The temperature and time must be well controlled, because insufficient condition may not cause the coarsening and decreasing precipitate among chips consolidation (Zhang T. et.
el., 2011).
4. Conclusion
Die performance revealed that extrusion die 12 gave more extrudability compared with extrusion die 6 where the tensile strength extruded using ER12 embarked 20-30% better than the tensile extruded using ER6.The properties of Aluminium alloy prepared with an increasing extrusion ratio, the yield strength, tensile and yield ratio increases. The corrosion resistance of specimens fabricated by solid-state can be improved by decreasing the grain size. The yield strength and ultimate tensile strength of as-extruded specimens are improved with rising extrusion ratio.
References
Misiolek W. Z., Haase M., Ben Khalifa N., Tekkaya A. E., Kleiner M. (2012), “High Quality Extrudates From Aluminum Chips By New Billet Compaction And Deformation Routes,” CIRP Ann. - Manuf. Technol., Vol. 61, No. 1, Pp. 239–242, Jan. 2012.
Gattmah, J., Ozturk, F., & Orhan, S. (2017). Effects of Process Parameters on Hot Extrusion of Hollow Tube. Arabian Journal for Science and Engineering.
https://doi.org/10.1007/s13369-017-2434-1
Chiba, R., & Yoshimura, M. (2015). Solid-state recycling of aluminium alloy swarf into c- channel by hot extrusion. Journal of Manufacturing Processes, 17, 1–8.
https://doi.org/10.1016/j.jmapro.2014.10.002
Tekkaya, A. E., Güley, V., Haase, M., & Jäger, A. (2012). Hot Extrusion of Aluminum Chips, 1559–1573.
Rahim S.N., Lajis M.A., Ariffin S. (2016) “Effect Of Extrusion Speed And Temperature On Hot Extrusion Process Of 6061 Aluminum Alloy Chip,” vol. 11, no. 4, pp. 2272–2277, 2016.
Haase, M., & Tekkaya, A. E. (2015). Cold extrusion of hot extruded aluminum chips. Journal
of Materials Processing Technology, 217, 356–367. https://doi.org/10.1016/j.jmatprotec.
Rahim, S. N. A., & Lajis, M. A. (2017). Mechanical Properties and Surface Integrity of Recycling Aluminum 6061 by Hot Extrusion Process, Materials Science Forum 894, 21- 24
Kamaruzaman, A. F., Zain, A. M., & Yusof, N. M. (2016). Optimization of Machining Parameters for Minimization of Roundness Error in Deep Hole Drilling using Minimum Quantity Lubricant, 1024.
Rahim, S. N. A., & Lajis, M. A. (2017). Effects on Mechanical Properties of Solid State Recycled Aluminium 6061 by Extrusion Material Processing, 730, 317–320.
https://doi.org/10.4028/www.scientific.net/KEM.730.317
Den Bakker A.J., Werkhoven R. J., Sillekens W. H., and Katgerman L. (2014), “The origin of weld seam defects related to metal flow in the hot extrusion of aluminium alloys EN AW-6060 and EN AW-6082,” J. Mater. Process. Technol., vol. 214, no. 11, pp. 2349–
2358, Nov. 2014.
Shokuhfar A. and Nejadseyfi O. (2014), “A comparison of the effects of severe plastic deformation and heat treatment on the tensile properties and impact toughness of aluminum alloy 6061,” Mater. Sci. Eng. A, vol. 594, pp. 140–148, Jan. 2014.
Rahim S.N., Lajis M.A., Ariffin S. (2016) “Effect Of Extrusion Speed And Temperature On Hot Extrusion Process Of 6061 Aluminum Alloy Chip,” vol. 11, no. 4, pp. 2272–2277, 2016.
Zhang T, Ji Z., Wu S. (2011), Effect of extrusion ratio on mechanical and corrosion properties of AZ31B alloys prepared by a solid recycling process, Materials and Design 32 (2011) 2742–2748
