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Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation
Materials Today: Proceedings xxx (xxxx) xxx
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Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation G.K. Manjunath a,⇑, K. Udaya Bhat b, G.V. Preetham Kumar b a b
School of Mechanical Engineering, REVA University, Kattigenahalli, Yelahanka, Bengaluru 560064, Karnataka, India Deptartment of Metallurgical & Materials Engineering, National Institute of Technology Karnataka, Surathkal, Mangaluru 575025, India
a r t i c l e
i n f o
Article history: Received 15 November 2019 Received in revised form 24 January 2020 Accepted 25 January 2020 Available online xxxx Keywords: ECAP Grain refinement Hardness Wear rate Wear surface morphology
a b s t r a c t Equal channel angular extrusion/pressing (ECAE/P) is an effectual technique to raise the mechanical, physical properties and resistance to wear of the materials. In this research, Al-5Zn-2Mg alloy material was ECAPed in route BC at lowest temperature. Hardness of the test material was increased after ECAE/P due to microstructure refinement. To demonstrate the wear characteristics of the Al-5Zn-2Mg alloy material after ECAE/P, wear tests (in dry sliding condition) were conducted at 2 conditions (condition 1: 19.62 N load and 1 m/s sliding speed, condition 2: 39.24 N load and 2 m/s sliding speed). The wear rate and magnitude of coefficient of friction (m) were lessened after ECAE/P. Abrasive, adhesive and oxidation wear mechanisms are the predominant wear mechanisms noticed in the ECAE/P processed billets. Along with these mechanisms relocation of iron elements from the counter body (disc) to the test material was noticed. Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
1. Introduction Al-Zn-Mg alloys are adopted in aircraft and structural applications. The presence of MgZn2 particles in these alloys imparts high strength which makes it worthwhile to use for numerous applications. Indeed, wear is an important property also influences life cycle of the products particularly in engineering applications. Wear resistance can be improved by several methods like coatings, heat treatment, alloying and severe plastic deformation (SPD) methods. Amongst them, SPD method is a promising technique to improve wear resistance via grain refinement. Equal channel angular extrusion/pressing (ECAE/P) is a promising SPD method to develop ultrafine grained (UFG) materials. Numerous literatures were stated to examine the importance of ECAP processing on Al-Zn-Mg alloys. Majority of the literature is on the wrought Al-Zn-Mg alloys. But, very few literatures were reported to examine the importance of the SPD and other metal forming processes on cast alloys composed of only aluminium, zinc and magnesium. Furthermore, most of the investigations on ECAP ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (G.K. Manjunath), [email protected] (K. Udaya Bhat), [email protected] (G.V. Preetham Kumar).
have been focused on microstructural characterization [1]. Few results were available on effect of ECAP and other SPD processes on wear behaviour of the materials [2]. But, consequence of ECAE/P on wear behaviour of Al-Zn-Mg alloy materials was not gained much attention. This draws attention in studying the wear behaviour of Al-Zn-Mg alloy materials. This research deals with the study of wear performance of Al-5Zn-2Mg alloy. The alloy composition studied in the present work closely matches the composition of the Al 7075 alloy. This alloy has various applications in the development of lightweight structures such as road tankers, transportable bridge girders, military vehicles and railway wagons. Also, this alloy is increasingly being used to manufacture hulls of ships. This alloy is a key engineering material for the application in the automotive and the aerospace parts due to their high strength, high toughness and low density.
2. Experimental procedure The Al-Zn-Mg alloy material containing 5%Zn, 2%Mg and remaining consists of Al was prepared by die casting, was used in this research. The composition of the material shown here are in weight %. The material was prepared in the form of circular billets of 25 mm diameter and 100 mm long. The alloy was prepared
https://doi.org/10.1016/j.matpr.2020.01.480 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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Fig. 1. Micrograph of the alloy material (a) initial as-cast condition and (b) after four ECAP passes.
Fig. 2. Hardness of the alloy material at various states. Fig. 4. Coefficient friction of the alloy material at various states.
Fig. 3. Wear rate of the alloy material at various states.
by melting the commercially pure aluminium, high purity zinc and high purity magnesium in a silicon carbide crucible [3]. Melting was carried out in electric resistance furnace. The melt was poured into a metal die which was preheated to 250 °C. The heat treatment of the material comprised of homogenization at 480 °C for
1200 min. Followed by the heat treatment, the alloy material was machined to 15.9 mm diameter and 80 mm long. The machined billets were pressed (ECAP processed) at pressing speed of 0.5 mm/s in a die having channels of 16 mm diameter and intersecting at 120°. With this angle, in each pass, a strain of 0.667 is imposed on the sample. The pressing was carried out in 40 T universal testing machine. Billets were pressed upto four passes using route BC at lowest temperature at which pressing was possible. To evade friction during pressing, material and die surfaces were applied with molybdenum disulphide. A separate heating arrangement was used for heating the die assembly to the required processing temperature. Die blocks were heated by using heating coils. Holes were drilled in the dies to insert the heating coils. These coils were controlled by a separate temperature controller. The ECAP die setup could be observed in our previous work [4]. Micrograph study of the as-cast, heat treated and pressed material was carried out in scanning electron microscope (SEM). The procedure for sample preparation for microstructure characterization is discussed in our previous study [5]. Microhardness of the material was determined by Vickers method by employing a mass of 50 gm for 15 sec and the hardness of the material was correlated to the wear performance of the material. Pin-on-disc test setup was employed to study the wear behaviour of the material at ambient temperature. For wear test experiments as-cast, heat treated and pressed billets were machined to 10 mm diameter and 28 mm length pins. Wear test were conducted at two test conditions. One test at 19.62 N load & 1 m/s sliding speed, and other one at 39.24 N load & 2 m/s sliding speed. Each of these tests
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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In this research, the billets were tried to press at least temperature [1]. Pressing was unproductive (failed) in the 1st pass at ambient temperature, 100 °C and 125 °C. At 150 °C, processing was productive (successful) and the material was deformed upto 4 passes in route BC.
Magnitude of the hardness of the alloy material in different conditions is depicted in Fig. 2. In as-cast and heat treated condition, the hardness of the billet measured is 90 Hv and 105 Hv, respectively. ECAP in route BC led to increase the 168 Hv in 1st pass, 192 Hv in the 2nd pass, 188 Hv in the 3rd pass and 200 Hv in the 4th pass, respectively. A little decrease in the magnitude of the hardness of the billet is noticed after third pass. The attributes for drop in the magnitude of the hardness after third pass is provided in our previous work [4]. After four passes, magnitude of the hardness was increased by 122%, from as-cast condition; which is accredited to the formation of large number of small sized subgrains and development of large quantity of dislocations between these sub-grains [9].
3.1. Microstructure and hardness
3.2. Wear behaviour
The micrograph of the alloy material in the initial as-cast and four ECAP pass sample is described in Fig. 1. The structure in ascast form is formed of dendrites in the a-Al matrix [6] with MgZn2 intermetallics in the inter-dendrites [7] as depicted in Fig. 1(a). In this state, dendrites approximately equal to 200 mm in size were perceived. After heat treatment cycle, large size grains nearly equal to 180 mm were perceived. ECAP in route BC led to form dislocation and shear bands in each pass. Due to relative movement of these dislocations and shear bands during processing, formation of sub-grains takes place which led to reduce in the grain size of the billet [8]. ECAP in route BC led to reduce the grain to 25 mm in 1st pass, 15 mm in 2nd pass, 6 mm in 3rd pass and 3 mm in 4th pass, respectively. Microstructure of the material after four passes is depicted in Fig. 1(b).
Fig. 3 depicts the magnitude of the wear rate (in 10 3 mm3/m) of the alloy material in various states. Effect of wear parameters and ECAP processing on the resistance to wear of the alloy material could be identified. As the first, less wear resistance was reported in as-cast material. The second finding is that, marginal improvement in resistance to wear of the alloy material was reported afterwards heat treatment cycle (homogenization) compared to as-cast material. The third finding is that, resistance to wear of the alloy material raised with the application of ECAP. The fourth finding is that, resistance to wear of the alloy material was improved with subsequent ECAP passes. The fifth finding is that, samples pressed upto four passes exhibited highest wear resistance. The sixth finding is that, resistance to wear of the alloy material dropped with raise in the applied load. Seventh finding is that, admirable wear
was taken place at a sliding distance of 1000 mm at 120 mm diameter track. To investigate the wear mechanisms and study the worn surfaces of as-cast, heat treated and pressed billets were examined in SEM equipped with EDS.
3. Results and discussion
Fig. 5. Worn surfaces and EDS report of the material after wear test at 19.62 N load & 1 m/s sliding speed (a) as-cast and (b) after heat treatment cycle.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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resistance was exhibited by ECAPed material even after raise in the applied load in contrast to as-cast and heat treated material. The eight finding is that, irrespective of the applied load samples pressed upto four passes exhibited highest wear resistance. This is accredited to the smallest grain size measured, highest hardness formed and development of large amount of high density of dislocations after four passes [10]. Fig. 4 depicts the magnitude of the ‘m’ (coefficient of friction) of the alloy material in various states. The ‘m’ of the material is calculated by using the relationship, Ff = m.N, where, m is the coefficient
of friction, Ff is the frictional force, and N is the applied load. The effect of wear parameters and ECAP on the magnitude of ‘m’ of the alloy material could be identified. As the first, magnitude of m is higher in as-cast material. The second finding is that, marginal drop in the magnitude of m of the alloy material was reported after heat treatment cycle (homogenization) compared to as-cast material. The third finding is that, magnitude of m of the alloy material decreased with the application of ECAP. The fourth finding is that, magnitude of m of the alloy material was dropped with subsequent ECAP passes. The fifth finding is that, samples pressed upto four
Fig. 6. Worn surfaces and EDS report of the material after wear test at 19.62 N load & 1 m/s sliding speed (a) 1 pass, (b) 2 pass (c) 3 pass and (d) 4 pass.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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Fig. 7. Worn surfaces and EDS report of the material after wear test at 39.24 N load & 2 m/s sliding speed (a) as-cast and (b) after heat treatment cycle.
passes exhibited lowest magnitude of m. The sixth finding is that, magnitude of m of the alloy material raised with raise in the applied load. The seventh finding is that, magnitude of m of the ECAPed alloy material reduced even after raise in the applied load in contrast to as-cast and heat treated material. The eight finding is that, irrespective of the applied load samples pressed upto four passes exhibited lowest magnitude of m. This is accredited to the highest refined microstructure produced after four ECAP passes. Fig. 5 depicts the worn surfaces and EDS report (wear test at 19.62 N load & 1 m/s sliding speed) of the as-cast and heat treated alloy material. Typical abrasive wear was observed in the worn faces of initial as-cast state and heat treated alloy material. The surfaces are damaged with the formation of crates and microgrooves. Also, oxidation effect was not detected in the EDS report. Fig. 6 depicts the worn surfaces and EDS report (wear test at 19.62 N load & 1 m/s sliding speed) of the alloy material after ECAP. In this case, the nature of wear is a combination of both abrasive and adhesive. In one pass sample, abrasive wear is dominant than the adhesive wear. This could be identified in Fig. 6(a). With subsequent passes, adhesive wear becomes dominant. This could be identified in Fig. 6(d). The change in the nature of wear from abrasive to adhesive afterwards ECAP is accredited to the refined microstructure during ECAP. EDS results indicate that the composition of the wear debris is composed of Al, Fe and O. The existence of Fe in debris was accredited to the relocation of Fe elements from the counter body (disc) to the test material [11]. The presence of O indicates the oxidation effect [12]. The formation of oxides in the debris is attributed the hardness increase after ECAP. Fig. 7 depicts the worn surfaces and EDS report (wear test at 39.24 N load & 2 m/s sliding speed) of the initial as-cast state and heat treated alloy material. The surfaces are severely damaged
indicating the clear nature of abrasive wear. The material from the test specimen is detached due to higher applied load at increased sliding speed. Also, grooves scratches are also identified. Also, oxidation effect was not observed in the EDS report of these samples. Fig. 8 depicts the worn surfaces and EDS report (wear test at 39.24 N load & 2 m/s sliding speed) of the material after ECAP. As compared to initial as-cast state and heat treated alloy material; surfaces were less damaged in ECAPed material indicating the existence of abrasive wear. This could be accredited to the hardness increase after ECAP. Interestingly, no adhesive effect was observed (as compared to wear effect observed in ECAPed material, wear test at 19.62 N load and 1 m/s sliding speed). Also, the composition of wear debris measured in the EDS analysis indicates the presence O in negligible quantity, suggesting the absence of oxidation effect. Interestingly, Fe quantity measured in the EDS analysis of wear debris is also in negligible quantity, suggesting the absence of Fe in pin surface. This is attributed to the rise in the sliding speed parameter of wear test. 4. Conclusions In this research, wear behaviour of Al-5Zn-2Mg alloy was subjected to ECAP was studied. Through the observed results the following conclusions are framed. The wear resistance of the material was improved and magnitude of m of was decreased after ECAP. This is accredited to the rise in the hardness due to microstructure refinement. The wear mechanism observed in unECAPed material was abrasive in nature. In ECAPed material abrasive, adhesive and oxidation mechanisms were reported.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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Fig. 8. Worn surfaces and EDS report of the material after wear test at 39.24 N load & 2 m/s sliding speed (a) 1 pass (b) 2 pass (c) 3 pass and (d) 4 pass.
Fe was identified in the composition of the wear debris stick to the sample surface. Findings from the current research could be adopted for better design of aerospace and structural equipments.
CRediT authorship contribution statement G.K. Manjunath: Conceptualization, Methodology, Investigation, Formal analysis, Writing - original draft. K. Udaya Bhat: Validation, Resources, Data curation, Writing - review & editing,
Supervision, Project administration. G.V. Preetham Kumar: Visualization, Supervision, Funding acquisition. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] R.Z. Valiev, T.G. Langdon, Prog. Mater. Sci. 51 (2006) 881–981.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
G.K. Manjunath et al. / Materials Today: Proceedings xxx (xxxx) xxx [2] N. Gao, C.T. Wang, R.J.K. Wood, T.G. Langdon, J. Mater. Sci. 47 (2012) 4779– 4797. [3] G.K. Manjunath, G.V. Preetham Kumar, K. Udaya Bhat, Trans. Indian Inst. Met. 70 (2017) 833–842. [4] G.K. Manjunath, G.V. Preetham Kumar, K. Udaya Bhat, P. Huilgol, J. Mater. Eng. Perform. 27 (2018) 5644–5655. [5] G.K. Manjunath, K. Udaya Bhat, G.V. Preetham Kumar, Metallogr. Microstruct. Anal. 7 (2018) 77–87. [6] O. Alvarez, C. Gonzalez, G. Aramburo, R. Herrera, J.A. Juarez-islas 402 (2005) 320–324.
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[7] S. Zhang, W. Hu, R. Berghammer, G. Gottstein, Acta Mater. 58 (2010) 6695– 6705. [8] M. Furukawa, Z. Horita, T.G. Langdon, Mater. Sci. Eng. A 332 (2002) 97–109. [9] K.R. Cardoso, D.N. Travessa, W.J. Botta, A.M.J. Jr, Mater. Sci. Eng. A 528 (2011) 5804–5811. [10] M.I.A.E. Aal, H. Seop, Mater. Des 53 (2014) 373–382. [11] M.I.A.E. Aal, N.E. Mahallawy, F.A. Shehata, M.A.E. Hameed, E.Y. Yoon, H.S. Kim, Mater. Sci. Eng. A 527 (2010) 3726–3732. [12] M. Chegini, M. Hossein, Mater. Charact. 140 (2018) 147–161.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation G.K. Manjunath a,⇑, K. Udaya Bhat b, G.V. Preetham Kumar b a b
School of Mechanical Engineering, REVA University, Kattigenahalli, Yelahanka, Bengaluru 560064, Karnataka, India Deptartment of Metallurgical & Materials Engineering, National Institute of Technology Karnataka, Surathkal, Mangaluru 575025, India
a r t i c l e
i n f o
Article history: Received 15 November 2019 Received in revised form 24 January 2020 Accepted 25 January 2020 Available online xxxx Keywords: ECAP Grain refinement Hardness Wear rate Wear surface morphology
a b s t r a c t Equal channel angular extrusion/pressing (ECAE/P) is an effectual technique to raise the mechanical, physical properties and resistance to wear of the materials. In this research, Al-5Zn-2Mg alloy material was ECAPed in route BC at lowest temperature. Hardness of the test material was increased after ECAE/P due to microstructure refinement. To demonstrate the wear characteristics of the Al-5Zn-2Mg alloy material after ECAE/P, wear tests (in dry sliding condition) were conducted at 2 conditions (condition 1: 19.62 N load and 1 m/s sliding speed, condition 2: 39.24 N load and 2 m/s sliding speed). The wear rate and magnitude of coefficient of friction (m) were lessened after ECAE/P. Abrasive, adhesive and oxidation wear mechanisms are the predominant wear mechanisms noticed in the ECAE/P processed billets. Along with these mechanisms relocation of iron elements from the counter body (disc) to the test material was noticed. Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
1. Introduction Al-Zn-Mg alloys are adopted in aircraft and structural applications. The presence of MgZn2 particles in these alloys imparts high strength which makes it worthwhile to use for numerous applications. Indeed, wear is an important property also influences life cycle of the products particularly in engineering applications. Wear resistance can be improved by several methods like coatings, heat treatment, alloying and severe plastic deformation (SPD) methods. Amongst them, SPD method is a promising technique to improve wear resistance via grain refinement. Equal channel angular extrusion/pressing (ECAE/P) is a promising SPD method to develop ultrafine grained (UFG) materials. Numerous literatures were stated to examine the importance of ECAP processing on Al-Zn-Mg alloys. Majority of the literature is on the wrought Al-Zn-Mg alloys. But, very few literatures were reported to examine the importance of the SPD and other metal forming processes on cast alloys composed of only aluminium, zinc and magnesium. Furthermore, most of the investigations on ECAP ⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (G.K. Manjunath), [email protected] (K. Udaya Bhat), [email protected] (G.V. Preetham Kumar).
have been focused on microstructural characterization [1]. Few results were available on effect of ECAP and other SPD processes on wear behaviour of the materials [2]. But, consequence of ECAE/P on wear behaviour of Al-Zn-Mg alloy materials was not gained much attention. This draws attention in studying the wear behaviour of Al-Zn-Mg alloy materials. This research deals with the study of wear performance of Al-5Zn-2Mg alloy. The alloy composition studied in the present work closely matches the composition of the Al 7075 alloy. This alloy has various applications in the development of lightweight structures such as road tankers, transportable bridge girders, military vehicles and railway wagons. Also, this alloy is increasingly being used to manufacture hulls of ships. This alloy is a key engineering material for the application in the automotive and the aerospace parts due to their high strength, high toughness and low density.
2. Experimental procedure The Al-Zn-Mg alloy material containing 5%Zn, 2%Mg and remaining consists of Al was prepared by die casting, was used in this research. The composition of the material shown here are in weight %. The material was prepared in the form of circular billets of 25 mm diameter and 100 mm long. The alloy was prepared
https://doi.org/10.1016/j.matpr.2020.01.480 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the International Mechanical Engineering Congress 2019: Materials Science.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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Fig. 1. Micrograph of the alloy material (a) initial as-cast condition and (b) after four ECAP passes.
Fig. 2. Hardness of the alloy material at various states. Fig. 4. Coefficient friction of the alloy material at various states.
Fig. 3. Wear rate of the alloy material at various states.
by melting the commercially pure aluminium, high purity zinc and high purity magnesium in a silicon carbide crucible [3]. Melting was carried out in electric resistance furnace. The melt was poured into a metal die which was preheated to 250 °C. The heat treatment of the material comprised of homogenization at 480 °C for
1200 min. Followed by the heat treatment, the alloy material was machined to 15.9 mm diameter and 80 mm long. The machined billets were pressed (ECAP processed) at pressing speed of 0.5 mm/s in a die having channels of 16 mm diameter and intersecting at 120°. With this angle, in each pass, a strain of 0.667 is imposed on the sample. The pressing was carried out in 40 T universal testing machine. Billets were pressed upto four passes using route BC at lowest temperature at which pressing was possible. To evade friction during pressing, material and die surfaces were applied with molybdenum disulphide. A separate heating arrangement was used for heating the die assembly to the required processing temperature. Die blocks were heated by using heating coils. Holes were drilled in the dies to insert the heating coils. These coils were controlled by a separate temperature controller. The ECAP die setup could be observed in our previous work [4]. Micrograph study of the as-cast, heat treated and pressed material was carried out in scanning electron microscope (SEM). The procedure for sample preparation for microstructure characterization is discussed in our previous study [5]. Microhardness of the material was determined by Vickers method by employing a mass of 50 gm for 15 sec and the hardness of the material was correlated to the wear performance of the material. Pin-on-disc test setup was employed to study the wear behaviour of the material at ambient temperature. For wear test experiments as-cast, heat treated and pressed billets were machined to 10 mm diameter and 28 mm length pins. Wear test were conducted at two test conditions. One test at 19.62 N load & 1 m/s sliding speed, and other one at 39.24 N load & 2 m/s sliding speed. Each of these tests
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
G.K. Manjunath et al. / Materials Today: Proceedings xxx (xxxx) xxx
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In this research, the billets were tried to press at least temperature [1]. Pressing was unproductive (failed) in the 1st pass at ambient temperature, 100 °C and 125 °C. At 150 °C, processing was productive (successful) and the material was deformed upto 4 passes in route BC.
Magnitude of the hardness of the alloy material in different conditions is depicted in Fig. 2. In as-cast and heat treated condition, the hardness of the billet measured is 90 Hv and 105 Hv, respectively. ECAP in route BC led to increase the 168 Hv in 1st pass, 192 Hv in the 2nd pass, 188 Hv in the 3rd pass and 200 Hv in the 4th pass, respectively. A little decrease in the magnitude of the hardness of the billet is noticed after third pass. The attributes for drop in the magnitude of the hardness after third pass is provided in our previous work [4]. After four passes, magnitude of the hardness was increased by 122%, from as-cast condition; which is accredited to the formation of large number of small sized subgrains and development of large quantity of dislocations between these sub-grains [9].
3.1. Microstructure and hardness
3.2. Wear behaviour
The micrograph of the alloy material in the initial as-cast and four ECAP pass sample is described in Fig. 1. The structure in ascast form is formed of dendrites in the a-Al matrix [6] with MgZn2 intermetallics in the inter-dendrites [7] as depicted in Fig. 1(a). In this state, dendrites approximately equal to 200 mm in size were perceived. After heat treatment cycle, large size grains nearly equal to 180 mm were perceived. ECAP in route BC led to form dislocation and shear bands in each pass. Due to relative movement of these dislocations and shear bands during processing, formation of sub-grains takes place which led to reduce in the grain size of the billet [8]. ECAP in route BC led to reduce the grain to 25 mm in 1st pass, 15 mm in 2nd pass, 6 mm in 3rd pass and 3 mm in 4th pass, respectively. Microstructure of the material after four passes is depicted in Fig. 1(b).
Fig. 3 depicts the magnitude of the wear rate (in 10 3 mm3/m) of the alloy material in various states. Effect of wear parameters and ECAP processing on the resistance to wear of the alloy material could be identified. As the first, less wear resistance was reported in as-cast material. The second finding is that, marginal improvement in resistance to wear of the alloy material was reported afterwards heat treatment cycle (homogenization) compared to as-cast material. The third finding is that, resistance to wear of the alloy material raised with the application of ECAP. The fourth finding is that, resistance to wear of the alloy material was improved with subsequent ECAP passes. The fifth finding is that, samples pressed upto four passes exhibited highest wear resistance. The sixth finding is that, resistance to wear of the alloy material dropped with raise in the applied load. Seventh finding is that, admirable wear
was taken place at a sliding distance of 1000 mm at 120 mm diameter track. To investigate the wear mechanisms and study the worn surfaces of as-cast, heat treated and pressed billets were examined in SEM equipped with EDS.
3. Results and discussion
Fig. 5. Worn surfaces and EDS report of the material after wear test at 19.62 N load & 1 m/s sliding speed (a) as-cast and (b) after heat treatment cycle.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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resistance was exhibited by ECAPed material even after raise in the applied load in contrast to as-cast and heat treated material. The eight finding is that, irrespective of the applied load samples pressed upto four passes exhibited highest wear resistance. This is accredited to the smallest grain size measured, highest hardness formed and development of large amount of high density of dislocations after four passes [10]. Fig. 4 depicts the magnitude of the ‘m’ (coefficient of friction) of the alloy material in various states. The ‘m’ of the material is calculated by using the relationship, Ff = m.N, where, m is the coefficient
of friction, Ff is the frictional force, and N is the applied load. The effect of wear parameters and ECAP on the magnitude of ‘m’ of the alloy material could be identified. As the first, magnitude of m is higher in as-cast material. The second finding is that, marginal drop in the magnitude of m of the alloy material was reported after heat treatment cycle (homogenization) compared to as-cast material. The third finding is that, magnitude of m of the alloy material decreased with the application of ECAP. The fourth finding is that, magnitude of m of the alloy material was dropped with subsequent ECAP passes. The fifth finding is that, samples pressed upto four
Fig. 6. Worn surfaces and EDS report of the material after wear test at 19.62 N load & 1 m/s sliding speed (a) 1 pass, (b) 2 pass (c) 3 pass and (d) 4 pass.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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Fig. 7. Worn surfaces and EDS report of the material after wear test at 39.24 N load & 2 m/s sliding speed (a) as-cast and (b) after heat treatment cycle.
passes exhibited lowest magnitude of m. The sixth finding is that, magnitude of m of the alloy material raised with raise in the applied load. The seventh finding is that, magnitude of m of the ECAPed alloy material reduced even after raise in the applied load in contrast to as-cast and heat treated material. The eight finding is that, irrespective of the applied load samples pressed upto four passes exhibited lowest magnitude of m. This is accredited to the highest refined microstructure produced after four ECAP passes. Fig. 5 depicts the worn surfaces and EDS report (wear test at 19.62 N load & 1 m/s sliding speed) of the as-cast and heat treated alloy material. Typical abrasive wear was observed in the worn faces of initial as-cast state and heat treated alloy material. The surfaces are damaged with the formation of crates and microgrooves. Also, oxidation effect was not detected in the EDS report. Fig. 6 depicts the worn surfaces and EDS report (wear test at 19.62 N load & 1 m/s sliding speed) of the alloy material after ECAP. In this case, the nature of wear is a combination of both abrasive and adhesive. In one pass sample, abrasive wear is dominant than the adhesive wear. This could be identified in Fig. 6(a). With subsequent passes, adhesive wear becomes dominant. This could be identified in Fig. 6(d). The change in the nature of wear from abrasive to adhesive afterwards ECAP is accredited to the refined microstructure during ECAP. EDS results indicate that the composition of the wear debris is composed of Al, Fe and O. The existence of Fe in debris was accredited to the relocation of Fe elements from the counter body (disc) to the test material [11]. The presence of O indicates the oxidation effect [12]. The formation of oxides in the debris is attributed the hardness increase after ECAP. Fig. 7 depicts the worn surfaces and EDS report (wear test at 39.24 N load & 2 m/s sliding speed) of the initial as-cast state and heat treated alloy material. The surfaces are severely damaged
indicating the clear nature of abrasive wear. The material from the test specimen is detached due to higher applied load at increased sliding speed. Also, grooves scratches are also identified. Also, oxidation effect was not observed in the EDS report of these samples. Fig. 8 depicts the worn surfaces and EDS report (wear test at 39.24 N load & 2 m/s sliding speed) of the material after ECAP. As compared to initial as-cast state and heat treated alloy material; surfaces were less damaged in ECAPed material indicating the existence of abrasive wear. This could be accredited to the hardness increase after ECAP. Interestingly, no adhesive effect was observed (as compared to wear effect observed in ECAPed material, wear test at 19.62 N load and 1 m/s sliding speed). Also, the composition of wear debris measured in the EDS analysis indicates the presence O in negligible quantity, suggesting the absence of oxidation effect. Interestingly, Fe quantity measured in the EDS analysis of wear debris is also in negligible quantity, suggesting the absence of Fe in pin surface. This is attributed to the rise in the sliding speed parameter of wear test. 4. Conclusions In this research, wear behaviour of Al-5Zn-2Mg alloy was subjected to ECAP was studied. Through the observed results the following conclusions are framed. The wear resistance of the material was improved and magnitude of m of was decreased after ECAP. This is accredited to the rise in the hardness due to microstructure refinement. The wear mechanism observed in unECAPed material was abrasive in nature. In ECAPed material abrasive, adhesive and oxidation mechanisms were reported.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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G.K. Manjunath et al. / Materials Today: Proceedings xxx (xxxx) xxx
Fig. 8. Worn surfaces and EDS report of the material after wear test at 39.24 N load & 2 m/s sliding speed (a) 1 pass (b) 2 pass (c) 3 pass and (d) 4 pass.
Fe was identified in the composition of the wear debris stick to the sample surface. Findings from the current research could be adopted for better design of aerospace and structural equipments.
CRediT authorship contribution statement G.K. Manjunath: Conceptualization, Methodology, Investigation, Formal analysis, Writing - original draft. K. Udaya Bhat: Validation, Resources, Data curation, Writing - review & editing,
Supervision, Project administration. G.V. Preetham Kumar: Visualization, Supervision, Funding acquisition. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References [1] R.Z. Valiev, T.G. Langdon, Prog. Mater. Sci. 51 (2006) 881–981.
Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480
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Please cite this article as: G. K. Manjunath, K. Udaya Bhat and G. V. Preetham Kumar, Dry sliding wear behaviour of Al-5Zn-2Mg alloy processed by severe plastic deformation, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.01.480