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Microstructural and Hardness evolution of AZ80 alloy after ECAP and post-ECAP processes
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 5 (2018) 17763–17768
www.materialstoday.com/proceedings
ICMPC_2018
Microstructural and Hardness evolution of AZ80 alloy after ECAP and post-ECAP processes Gajanan M Naik1*, Gopal D Gote1, Narendranath S1 1
Department of Mechanical Engineering, National Institute of Technology, Karnataka, Surathkal, India
Abstract This research paper investigates the microstructure evolution and hardness variation of wrought AZ80 magnesium alloy after each ECAP passes. The strengthening effect of AZ80 alloy was examined after post-ECAP aging treatment. Alloys were severely deformed through equal channel angular press at 533K using route Bc with a die channel angle (ϕ) 1100 and corner angle (ψ) 300. Subsequently, the microstructural characterization was studied using optical microscope (OM) and scanning electron microscope (SEM). Further, post-ECAP aging treatment at 523K for 6h and 12h was performed and microhardness of the specimens was measured. It was found that the grain refinement through thermo-mechanical processing of ECAP and Post-ECAP treatment significantly improves the microhardness of the Mg alloy, which directly influences the properties of wrought AZ80 magnesium alloy. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: ECAP; AZ80; Microhardness; grain size.
1. Introduction In the last decade, the ultra-fine grain structure is achieved by severe plastic deformation (SPD) technique in order to obtain higher strength and ductility for structural applications [1, 3]. The above properties were achieved by grain refinement through SPD. There are several types of SPD methods to generate UFG structures such as equalchannel angle pressing (ECAP), high-pressure torsion (HPT), accumulated roll-bonding (ARB), multi-directional forging (MDF), repetitive corrugation and straightening (RCS), twist extrusion (TE) [2,4]. * Corresponding author. Tel.: +91-776-000-6193 E-mail address: [email protected]
2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.
17764
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
Out of all SPD techniques, equal channel angular press (ECAP) is a promising and capable technique to achieve micro/Nano-grain structure in a bulk material which improves the material properties. Also, this variation of materials properties depends on ECAP processing routes and post ECAP treatment. T. Tański et al. [5] have studied the grain refinement and strengthening of aluminum-based alloys (Al–Mg) through ECAP and post-ECAP. It was revealed that heat treatment before and after ECAP, significantly affect and improves mechanical properties of aluminum alloys. It was also demonstrated that the ECAP causes grain refinement which directly influences on properties of Al-Mg alloys and an increase of strength and ductility was achieved. Magnesium alloys are difficult to deform and low strength engineering material because of less slip system of Mg alloys [7]. An efficient way to increase the magnesium alloy properties of i.e AZ80 alloys is through grain refinement using equal channel angular pressing. The authors noticed inadequate work was done on the AZ80 wrought alloy. Therefore the present work presents the microstructure and micro-hardness of ECAP processed and post-ECAP treated AZ80 magnesium alloy. 2. Experimental work A commercial wrought AZ80 billet was homogenized and solution treated at 400 °C for 15 h and then furnace cooled. Circular rod of 16mm diameter and 80 mm length were machined and processed through ECAP die which is having a channel angle of 1100 and corner angle of 300 shown in Fig 1 (a) also the route BC and working temperature of 533K (Tdeformation= 0.4Tm), Molybdenum disulfide (MoS2) lubricant is applied on samples and pressed at the rate of 1mm/sec during experimentation. The ECAP processed AZ80 sample have shown in Fig 1 (b), after two passes (2P) and four ECAP passes (4P) samples were prepared for microstructural characterization. Post-ECAP treatment was carried out at 523K for 6h and 12h. Samples for OM and SEM investigation were polished by mechanical polishing and further etched in a solution of 4.2g picric acid, 10ml acetic acid, 10ml distilled water and 70ml ethanol for 3-5s. Microstructures and elements distributions were observed and analyzed by Optical microscopy (BIOVIS material plus), Scanning Electron Microscopy (Model: JEO JSM–638OLA from JEOL, USA) operated at 30kV; Magnification range-3,00,000X and micro-hardness (Model: MVH–S–AUTO from OMNI TECH, PUNE, INDIA) of 100gm load was applied for dwell of 13 s.[8]
Fig. 1. a) Equal Channel Angular Press Die
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
17765
Fig. 1. b) ECAP processed sample
3. Results and Discussion 3.1. Microstructure evolution The microstructure of the ECAPed sample was investigated by both the optical microscope and scanning electron microscope to reveal the average grain size and possible presence of undissolved secondary phase particles. The presence of secondary β-Mg17Al12 phases in an as-received wrought AZ80 Mg alloy was shown in Fig 2 (a-f). The ultra-fine microstructure was formed by fully recrystallized equiaxed grains with the average grain size of ~ 12 µm during ECAP 4th pass. Indeed, evolution of grain refinement by ECAP processing primarily by dynamic recrystallization (DRX) [9,10]. The solution treatment after ECAP process (post-ECAP) resulted in the full dissolution of the secondary phases, which was typically present in the as-received alloy. Figure 2 shows the microstructure of wrought AZ80 magnesium alloys of as-received, homogenized, ECAPed and post-ECAPed samples. The microstructure clearly shown the grain size reduction and spreading of β-second phases, this can be clearly observed and presented in the micrographs (Fig 2). The microstructure along the flow direction of the sample after second passes and fourth passes of ECAP yields ~32µm to ~12µm respectively. It is readily apparent from this study that there are eutectic phases precipitates and typically distributed along the grain boundaries after post-ECAP annealing treatment of wrought AZ80 Mg alloy. Tianping Zhu, et al.[6] was observed the existence of irregular eutectic phases during annealing treatment for AZ91 magnesium alloys during his study. Also, the ECAP die configuration induces a shear strain of ~0.74 per pass, so second and fourth pass correspond to a total strain of ~1.4 and ~2.9 respectively.
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Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
Fig. 2. Microstructure of wrought AZ80 alloy a) As-received b) As-received SEM image c) Homogenized at 4000C for 15h d) 2P-ECAP e) 4PECAP f) 2P-ECAP- 12h at 523K
3.2. Hardness evolution The average micro-hardness results for as-received, Homogenized, ECAP processed and post-treated samples are illustrated in Fig 3. Hardness evolution occurring during the ECAP and post-ECAP samples of wrought AZ80 Mg alloys have shown significant improvement. Initially the average micro-hardness of the as-received AZ80 material is obtained to be 65 HV further the micro-hardness of homogenized sample was increased to 67 Hv. As the ECAP pass increases, microhardness also increased to 76 HV for ECAP 2-pass and 87 HV for ECAP 4-passes and also, the increased microhardness was observed even after solution treatment at 523K for 2P and 4P ECAP processed samples with respect to 6h and 12h aging (Fig 3). This Increase in hardness due to the effect of strain hardening and uniform distribution of secondary phases during ECAP and post ECAP treatment [10], distribution of secondary phases during ECAP and solution treatment was evidently shown in Fig 2. Therefore, from the study it is observed that the micro-hardness of the wrought AZ80 alloy increases with the increase of ECAP passes and aging time A. Dhal et al [3] was observed the similar trend during ECAP and post-ECAP study on aluminum alloys.
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
17767
Micro-Hardness
Micro-Hardness (Hv)
95 90 85 80 75 70 65 60 As-Received 0P
2P
2P-6h 2P-12h
4P
4P-6h 4P-12h
ECAP Passes Fig. 3. Variations of microhardness after ECAP and post-ECAP
4. Conclusions The ECAP and post-ECAP processing experiments were carried out on AZ80 wrought magnesium alloy to enhance the micro-hardness of the alloy by achieving ultra-fine structure and post-heat treatment. Based on the obtained results from the present study, some important conclusions were drawn as follows. 1. Microstructural observations demonstrated that there is a significant grain refinement through the ECAP process, an average grain size of ~ 12µm was achieved after 4 ECAP passes. Additionally, fine grained microstructures showed a significantly increased micro-hardness. 2. The post-ECAP annealing at 523 K for 6 h and 12h, precipitates eutectic phases along the grain boundary which contributes improved micro-hardness. Acknowledgment The authors are very grateful to the DRDO-NRB, Government of India, grant number: NRB/4003/PG/366. Mr.Anjan B N and Mr. Praveen for their support during the experimentation.
thanks to
Also
References [1] S. Zhao, C. Meng, F. Mao, and W. Hu, Influence of severe plastic deformation on dynamic strain aging of ultrafine grained Al – Mg alloys’, Acta Materialia, vol. 76, pp. 54–67, 2014. [2] W. Chengpeng, L. Fuguo, C. Bo, Y. Zhanwei, and L. Hongya, ‘Severe Plastic Deformation Techniques for Bulk Ul- trafine-grained Materials’, Rare Metal Materials and Engineering, vol. 41, no. 6, pp. 941–946, 2012. [3] A. Dhal, S. K. Panigrahi, and M. S. Shunmugam, ‘Insight into the microstructural evolution during cryo-severe plastic deformation and postdeformation annealing of aluminum and its alloys’, J. Alloys Compd., vol. 726, pp. 1205–1219, 2017. [4] S. A. Alsubaie, Y. Huang, and T. G. Langdon, ‘Hardness evolution of AZ80 magnesium alloy processed by HPT at different temperatures’, j. mater res technol . vol. 6, no. 4, pp. 378–384, 2017. [5] T. Ta, P. Snopi, W. Pakie, W. Borek, K. Prusik, and S. Rusz, ‘Structure and properties of AlMg alloy after combination of ECAP and postECAP ageing’, archives of civil and mechanical engineering, vol. 6, 2015.
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Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
[6] T. Zhu, Z. W. Chen, and W. Gao, ‘Dissolution of Eutectic b -Mg 17 Al 12 Phase in Magnesium AZ91 Cast Alloy at Temperatures Close to Eutectic Temperature’, Journal of Materials Engineering and Performance, vol. 19, no. August, pp. 860–867, 2010. [7] M. Avvari, S. Narendranath, and M. Able, ‘Microstructure evolution in AZ61 alloy processed by equal channel angular pressing’, Journal of Materials Engineering and Performance, vol. 8, no. 6, pp. 1–9, 2016. [8] K. R. Gopi and H. S. Nayaka, ‘ Microstructure and mechanical properties of magnesium alloy processed by equal channel angular pressing ( ECAP )’, Mater. Today Proc., vol. 4, no. 9, pp. 10288–10292, 2017. [9] P. Minárik, J. Veselý, R. Král, and J. Bohlen, ‘Exceptional mechanical properties of ultra- fi ne grain Mg-4Y-3RE alloy processed by ECAP’, Materials Science & Engineering, vol. 708, no. September, pp. 193–198, 2017. [10] K. R. G. H. Shivananda and N. Sandeep, ‘Microstructural Evolution and Strengthening of AM90 Magnesium Alloy Processed by ECAP’, Arab. J. Sci. Eng., vol. 42, no. 11, pp. 4635–4647, 2017.
ScienceDirect Materials Today: Proceedings 5 (2018) 17763–17768
www.materialstoday.com/proceedings
ICMPC_2018
Microstructural and Hardness evolution of AZ80 alloy after ECAP and post-ECAP processes Gajanan M Naik1*, Gopal D Gote1, Narendranath S1 1
Department of Mechanical Engineering, National Institute of Technology, Karnataka, Surathkal, India
Abstract This research paper investigates the microstructure evolution and hardness variation of wrought AZ80 magnesium alloy after each ECAP passes. The strengthening effect of AZ80 alloy was examined after post-ECAP aging treatment. Alloys were severely deformed through equal channel angular press at 533K using route Bc with a die channel angle (ϕ) 1100 and corner angle (ψ) 300. Subsequently, the microstructural characterization was studied using optical microscope (OM) and scanning electron microscope (SEM). Further, post-ECAP aging treatment at 523K for 6h and 12h was performed and microhardness of the specimens was measured. It was found that the grain refinement through thermo-mechanical processing of ECAP and Post-ECAP treatment significantly improves the microhardness of the Mg alloy, which directly influences the properties of wrought AZ80 magnesium alloy. © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization. Keywords: ECAP; AZ80; Microhardness; grain size.
1. Introduction In the last decade, the ultra-fine grain structure is achieved by severe plastic deformation (SPD) technique in order to obtain higher strength and ductility for structural applications [1, 3]. The above properties were achieved by grain refinement through SPD. There are several types of SPD methods to generate UFG structures such as equalchannel angle pressing (ECAP), high-pressure torsion (HPT), accumulated roll-bonding (ARB), multi-directional forging (MDF), repetitive corrugation and straightening (RCS), twist extrusion (TE) [2,4]. * Corresponding author. Tel.: +91-776-000-6193 E-mail address: [email protected]
2214-7853 © 2018 Elsevier Ltd. All rights reserved. Selection and/or Peer-review under responsibility of Materials Processing and characterization.
17764
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
Out of all SPD techniques, equal channel angular press (ECAP) is a promising and capable technique to achieve micro/Nano-grain structure in a bulk material which improves the material properties. Also, this variation of materials properties depends on ECAP processing routes and post ECAP treatment. T. Tański et al. [5] have studied the grain refinement and strengthening of aluminum-based alloys (Al–Mg) through ECAP and post-ECAP. It was revealed that heat treatment before and after ECAP, significantly affect and improves mechanical properties of aluminum alloys. It was also demonstrated that the ECAP causes grain refinement which directly influences on properties of Al-Mg alloys and an increase of strength and ductility was achieved. Magnesium alloys are difficult to deform and low strength engineering material because of less slip system of Mg alloys [7]. An efficient way to increase the magnesium alloy properties of i.e AZ80 alloys is through grain refinement using equal channel angular pressing. The authors noticed inadequate work was done on the AZ80 wrought alloy. Therefore the present work presents the microstructure and micro-hardness of ECAP processed and post-ECAP treated AZ80 magnesium alloy. 2. Experimental work A commercial wrought AZ80 billet was homogenized and solution treated at 400 °C for 15 h and then furnace cooled. Circular rod of 16mm diameter and 80 mm length were machined and processed through ECAP die which is having a channel angle of 1100 and corner angle of 300 shown in Fig 1 (a) also the route BC and working temperature of 533K (Tdeformation= 0.4Tm), Molybdenum disulfide (MoS2) lubricant is applied on samples and pressed at the rate of 1mm/sec during experimentation. The ECAP processed AZ80 sample have shown in Fig 1 (b), after two passes (2P) and four ECAP passes (4P) samples were prepared for microstructural characterization. Post-ECAP treatment was carried out at 523K for 6h and 12h. Samples for OM and SEM investigation were polished by mechanical polishing and further etched in a solution of 4.2g picric acid, 10ml acetic acid, 10ml distilled water and 70ml ethanol for 3-5s. Microstructures and elements distributions were observed and analyzed by Optical microscopy (BIOVIS material plus), Scanning Electron Microscopy (Model: JEO JSM–638OLA from JEOL, USA) operated at 30kV; Magnification range-3,00,000X and micro-hardness (Model: MVH–S–AUTO from OMNI TECH, PUNE, INDIA) of 100gm load was applied for dwell of 13 s.[8]
Fig. 1. a) Equal Channel Angular Press Die
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
17765
Fig. 1. b) ECAP processed sample
3. Results and Discussion 3.1. Microstructure evolution The microstructure of the ECAPed sample was investigated by both the optical microscope and scanning electron microscope to reveal the average grain size and possible presence of undissolved secondary phase particles. The presence of secondary β-Mg17Al12 phases in an as-received wrought AZ80 Mg alloy was shown in Fig 2 (a-f). The ultra-fine microstructure was formed by fully recrystallized equiaxed grains with the average grain size of ~ 12 µm during ECAP 4th pass. Indeed, evolution of grain refinement by ECAP processing primarily by dynamic recrystallization (DRX) [9,10]. The solution treatment after ECAP process (post-ECAP) resulted in the full dissolution of the secondary phases, which was typically present in the as-received alloy. Figure 2 shows the microstructure of wrought AZ80 magnesium alloys of as-received, homogenized, ECAPed and post-ECAPed samples. The microstructure clearly shown the grain size reduction and spreading of β-second phases, this can be clearly observed and presented in the micrographs (Fig 2). The microstructure along the flow direction of the sample after second passes and fourth passes of ECAP yields ~32µm to ~12µm respectively. It is readily apparent from this study that there are eutectic phases precipitates and typically distributed along the grain boundaries after post-ECAP annealing treatment of wrought AZ80 Mg alloy. Tianping Zhu, et al.[6] was observed the existence of irregular eutectic phases during annealing treatment for AZ91 magnesium alloys during his study. Also, the ECAP die configuration induces a shear strain of ~0.74 per pass, so second and fourth pass correspond to a total strain of ~1.4 and ~2.9 respectively.
17766
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
Fig. 2. Microstructure of wrought AZ80 alloy a) As-received b) As-received SEM image c) Homogenized at 4000C for 15h d) 2P-ECAP e) 4PECAP f) 2P-ECAP- 12h at 523K
3.2. Hardness evolution The average micro-hardness results for as-received, Homogenized, ECAP processed and post-treated samples are illustrated in Fig 3. Hardness evolution occurring during the ECAP and post-ECAP samples of wrought AZ80 Mg alloys have shown significant improvement. Initially the average micro-hardness of the as-received AZ80 material is obtained to be 65 HV further the micro-hardness of homogenized sample was increased to 67 Hv. As the ECAP pass increases, microhardness also increased to 76 HV for ECAP 2-pass and 87 HV for ECAP 4-passes and also, the increased microhardness was observed even after solution treatment at 523K for 2P and 4P ECAP processed samples with respect to 6h and 12h aging (Fig 3). This Increase in hardness due to the effect of strain hardening and uniform distribution of secondary phases during ECAP and post ECAP treatment [10], distribution of secondary phases during ECAP and solution treatment was evidently shown in Fig 2. Therefore, from the study it is observed that the micro-hardness of the wrought AZ80 alloy increases with the increase of ECAP passes and aging time A. Dhal et al [3] was observed the similar trend during ECAP and post-ECAP study on aluminum alloys.
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
17767
Micro-Hardness
Micro-Hardness (Hv)
95 90 85 80 75 70 65 60 As-Received 0P
2P
2P-6h 2P-12h
4P
4P-6h 4P-12h
ECAP Passes Fig. 3. Variations of microhardness after ECAP and post-ECAP
4. Conclusions The ECAP and post-ECAP processing experiments were carried out on AZ80 wrought magnesium alloy to enhance the micro-hardness of the alloy by achieving ultra-fine structure and post-heat treatment. Based on the obtained results from the present study, some important conclusions were drawn as follows. 1. Microstructural observations demonstrated that there is a significant grain refinement through the ECAP process, an average grain size of ~ 12µm was achieved after 4 ECAP passes. Additionally, fine grained microstructures showed a significantly increased micro-hardness. 2. The post-ECAP annealing at 523 K for 6 h and 12h, precipitates eutectic phases along the grain boundary which contributes improved micro-hardness. Acknowledgment The authors are very grateful to the DRDO-NRB, Government of India, grant number: NRB/4003/PG/366. Mr.Anjan B N and Mr. Praveen for their support during the experimentation.
thanks to
Also
References [1] S. Zhao, C. Meng, F. Mao, and W. Hu, Influence of severe plastic deformation on dynamic strain aging of ultrafine grained Al – Mg alloys’, Acta Materialia, vol. 76, pp. 54–67, 2014. [2] W. Chengpeng, L. Fuguo, C. Bo, Y. Zhanwei, and L. Hongya, ‘Severe Plastic Deformation Techniques for Bulk Ul- trafine-grained Materials’, Rare Metal Materials and Engineering, vol. 41, no. 6, pp. 941–946, 2012. [3] A. Dhal, S. K. Panigrahi, and M. S. Shunmugam, ‘Insight into the microstructural evolution during cryo-severe plastic deformation and postdeformation annealing of aluminum and its alloys’, J. Alloys Compd., vol. 726, pp. 1205–1219, 2017. [4] S. A. Alsubaie, Y. Huang, and T. G. Langdon, ‘Hardness evolution of AZ80 magnesium alloy processed by HPT at different temperatures’, j. mater res technol . vol. 6, no. 4, pp. 378–384, 2017. [5] T. Ta, P. Snopi, W. Pakie, W. Borek, K. Prusik, and S. Rusz, ‘Structure and properties of AlMg alloy after combination of ECAP and postECAP ageing’, archives of civil and mechanical engineering, vol. 6, 2015.
17768
Gajanan M Naik et al./ Materials Today: Proceedings 5 (2018) 17763–17768
[6] T. Zhu, Z. W. Chen, and W. Gao, ‘Dissolution of Eutectic b -Mg 17 Al 12 Phase in Magnesium AZ91 Cast Alloy at Temperatures Close to Eutectic Temperature’, Journal of Materials Engineering and Performance, vol. 19, no. August, pp. 860–867, 2010. [7] M. Avvari, S. Narendranath, and M. Able, ‘Microstructure evolution in AZ61 alloy processed by equal channel angular pressing’, Journal of Materials Engineering and Performance, vol. 8, no. 6, pp. 1–9, 2016. [8] K. R. Gopi and H. S. Nayaka, ‘ Microstructure and mechanical properties of magnesium alloy processed by equal channel angular pressing ( ECAP )’, Mater. Today Proc., vol. 4, no. 9, pp. 10288–10292, 2017. [9] P. Minárik, J. Veselý, R. Král, and J. Bohlen, ‘Exceptional mechanical properties of ultra- fi ne grain Mg-4Y-3RE alloy processed by ECAP’, Materials Science & Engineering, vol. 708, no. September, pp. 193–198, 2017. [10] K. R. G. H. Shivananda and N. Sandeep, ‘Microstructural Evolution and Strengthening of AM90 Magnesium Alloy Processed by ECAP’, Arab. J. Sci. Eng., vol. 42, no. 11, pp. 4635–4647, 2017.