MICROSTRUCTURAL STUDIES ZE41 RARE EARTH ALLOY USING SEM

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 6, June 2017, pp , Article ID: IJMET_08_06_076 Available online at aeme/ijm MET/issues.as asp?jtype=ijm MET&VType=8&IType= =6 ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed MICROSTRUCTURAL STUDIES OF MAGNESIUM ZE41 RARE EARTH ALLOY USING SEM C Sailaja Associate Professor, Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad, Telangana, India N Anuradha Associate Professor, Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad, Telangana, India P Geeta Krishna Assistant Professor, Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad, Telangana, India B Ramgopal Reddy Associate Professor, Department of Mechanical Engineering, RVRR & JC college of Engineering, Guntur, Andhra Pradesh, India ABSTRACT Magnesium alloys are the lightest of all structural metals and has an excellent damping characteristics, high strength-to-weight ratio, good castability and excellent machinability. The magnesium ZE41 rare earth alloy has a potential application in automotive & aerospace sectors as a structural material. The ZE41 alloy consists of gadolinium (Gd) and Neodymium (Nd) as rare earth elements and it has 2% ductility and one slip system at 200 C. In the present study, an attempt was made to evaluate the microstructural features of magnesium ZE41 rare earth alloy in different states. The surface morphology of the ZE41 alloy is analyzed using Scanning electron microscope (SEM). The results indicates that the microstructure of ZE41 alloy consists of α-mg matrix which forms main body of the grain along with secondary phases, consisting of randomly distributed β-phase particles and eutectically distributed T-Phase at the grain boundaries were observed with a magnification of X100 and X2000 respectively. Key words: SEM, Magnesium ZE41 alloy, Microstructure and Rare Earth. 722

2 C Sailaja, N Anuradha, P Geeta Krishna and B Ramgopal Reddy Cite this Article: C Sailaja, N Anuradha, P Geeta Krishna and B Ramgopal Reddy. Microstructural Studies of Magnesium ZE41 Rare Earth Alloy using SEM. International Journal of Mechanical Engineering and Technology, 8(6), 2017, pp INTRODUCTION Reduction of weight in automobiles and aerospace components are one of the most effective ways of improving the resistance of a vehicle to rolling, climbing and acceleration is directly dependent on its mass. consequently, research activities in aerospace and automobile industry has been increased in replacing heavy material to light weight materials such as magnesium based alloys, aluminium based alloys etc. magnesium alloys are lighter than aluminium alloys therefore, expected to find increased applications in automobile and aerospace sectors. although magnesium alloys have a variety of excellent properties, including a high strengthto-weight ratio, low density, dimensional stability and castability, the high corrosion susceptibility of magnesium alloys, particularly galvanic corrosion, retards their wider application in industry. there are various kinds of alloys available commercially and those are categorized into gravity-casting alloys and die-casting alloys. die casting alloys does not exhibit the adequate combination of castability, creep performance, corrosion resistance, ambient strength and reasonable cost to meet the requirement for manufacturing. magnesium ZE41 alloy is most commonly used for gravity casting which has limited creep resistance and corrosion properties due to the rare earth element present in it. The present work deals with the microstructural studies using scanning electron microscope (SEM) on magnesium ZE41 rare earth alloy. 2. EXPERIMENTAL DETAILS 2.1. Material Specifications Before any study carried out on a material its chemical composition must be known. The alloy which was used in this study was cast 20mm thick blocks of ZE41 rare earth alloy. Chemical analysis of the ZE41 rare earth alloy was carried out using atomic emission spectroscope and are reported in the table 1. Chemical Analysis (%) Table 1 Chemical analysis of ZE41 Rare Earth alloy Nd Ce Mn Fe Ni Zr Zn Cu La Pr Mg Observed values Rem Specified Min values Max Rare earth elements present in this alloy are Gadolinium (Gd) and Neodymium (Nd) and they account for % (wt) Equipment To study the surface interaction of the ZE41 alloy Scanning electron microscope of Hitachi S- 3400N were used. This kind of microscope is widely used in laboratory to investigate the microstructures of the metals and non metals. 723 com

3 Microstructural Studies of Magnesium ZE41 Rare Earth Alloy using SEM Figure 1 Scanning Electron Microscope (Hitachi S-3400N) Accelerated electrons in an SEM carry significant amounts of kinetic energy, and this energy is dissipatedd as a variety of signals producedd by electron-sample interactions when the incident electrons are decelerated in the solid sample. These signals include secondary electrons (that produce SEM images), backscattered electrons (BSE),( diffracted backscattered electrons (EBSD that are used to determine crystal structures and orientations of minerals), photons (characteristic X-rays that are used for elemental analysis and continuum X-rays), visible light (cathodoluminescence CL), and heat. Secondary electrons and backscattered electrons are commonly used for imagingg samples: secondary electrons are most valuable for showing morphology and topography on sampless and backscattered electrons are most valuable for illustrating contrasts in composition in multiphasee samples (i.e. for rapid phase discrimination). X-ray generation is produced by inelastic collisions of the incident electrons with electrons in discrete orbital s (shells) of atoms in the sample. As the excited electrons return to lower energy states, they yield X-rays thatt are of a fixed wavelength (that is related to the difference in energy levels of electrons in different shells for a given element). Thus, characteristic X-rays are produced for each element in a mineral that is "excited"" by the electron beam. SEM analysis is considered to be "non-destructive"; that is, x-rays generated by electron interactions do not lead to volume loss of the sample, so it is possible to analyze the same materials repeatedly Experimental Procedure Magnesium ZE41 Rare Earth alloy (Specification: ASTM B80) specimens of size 15mm X 15mm X 1mm were cut using CNCC wire cut EDM machine for Scanning Electron Microscope (SEM). Specimens were examined using Hitachi S-3400N SEM-EDX which is incorporated for elemental analysis. Most images were acquired using an accelerating voltage of 20 KeV and a working distance of approximate ely 6.2mm-7.double sided conductive carbon tape, thus mm. All specimens were grounded to the SEM Stub of diameter 50mm using ensuring electrical conductionn though the carbon tape. 3. RESULTS AND DISCUSSION The optical micrograph shown in the figure 2 is taken from a ZE41 rare alloy plate shows an equiaxed grain structure of α-mg typical of a casting. 724

4 C Sailaja, N Anuradha, P Geeta Krishna and B Ramgopal Reddy Figure 2 Optical Micrograph of ZE41 Rare Earth Alloy Figure 3 Shows typical SEM micrographs of the surface of ZE41 (Fig. 3 a, b and c) and there were large regions of attack within the centree of the grains (dark regions), and some attack around the grain boundaries. This is seen clearly in the SEM micrograph (Fig. 3a). The dark regions in the centre of the grains have the appearance of deep craters, along with fine pitting covering the remainderr of the surface within the grains. A phase thought to be T-phase (Mg7Zn3RE) is clearly visible at the grain boundaries. Some larger intermetallic particles were also observed within the grains. The same microstructural features were observed in the SEM (Fig. 3 b) with the grain boundary T-phase appearing as a white network. (a) (b) (c) Figure 3 SEM Micrograph of ZE41 surface (a) WD: 6.8mm (b) WD: 7.1mmm (c) WD: 7.2mm 725

5 Microstructural Studies of Magnesium ZE41 Rare Earth Alloy using SEM The zones rich in Zr (interaction zones), are identified by Scanning electron microscopy, were clearly visible in the centers of the grains when imaged in SEM (Fig. 4 a, b and c). A dispersion of the T-phase (Mg7Zn3RE) at the grain boundaries, and larger, darker cloudy regions associated with Zr-rich areas in the grains are clearly visible. The grain boundaries are well defined, seen as clouds in the ZE41 alloy, whereas the grain boundaries were defined by the semi-continuous network of T-phase. The SEM image also revealed a light coloured zone within most of the grains. Particles were clearly present within these zones and they were rich in Zr with some Zn but contained very little Mg. (a) (b) (c) Figure 4 SEM Micrograph of a polished surfaces SEM micrographs taken at 2 hours and 3 hours respectively of immersion in M NaCl is shown in Fig. 6; (a) and (b). Images are with corrosion product removed. After 2 hour immersion, only some grain boundary attack was present, but initial pitting around the Zr Zn particles in the Zr-rich zone within the grains is evident. After 3 h, there was a greater degree of grain boundary attack, with the pitting inside the Zr-rich zone more advanced. 726

6 C Sailaja, N Anuradha, P Geeta Krishna and B Ramgopal Reddy (a) (b) Figure 5 SEM Micrograph of ZE41 after immersing in M NaCl and removed at (a) 2hours and (b) 3 hours 4. CONCLUSIONS This paper discusses microstructural studies of a newly developed magnesium ZE41 rare earth alloy. The microstructur ral features ZE41 which was obtained usingg Scanning Electron Microscopy consists of grain boundary precipitates containing Zn and Ce, α-mg grains possibly containing fine β-precipitates, and Zr-rich intermetallic particles often observed within a Zr-rich interaction zone. Galvanic corrosion on ZE41 rare earth alloy altered the microstructure by changing the distribution of the grain boundary T-phase (Mg7Zr3RE), ZE41 alloy specimens after immersion in M NaCl consisted of grain boundary attack propagating in the form of corrosion filaments, with no observed pitting in the centre of the grains. The sequence of corrosion initiation and propagation involved corrosion filaments initiating at the grain boundaries, and corrosion filaments following along grain boundary paths. These filaments progress into the α-mg grain until they meet the Zr-rich regions. REFERENCES [1] P. Volovitch, J.E. Masse, A. Fabre, L. Barrallier, W. Saikaly. Microstructure and Corrosion Resistance of Magnesium Alloy ZE41 with Laser Surface Cladding by Al Si Powder. Surface Coatings & Technology, 202, 2008, pp [2] W.C. Neil, M. Forsyth, P.C. Howlett, C.R. Hutchinson, B..R.W. Hinton, Corrosion of Heat Treated Magnesium Alloy ZE41, Corrosion Science, 53, 2011, pp [3] W.C. Neil, M. Forsyth, P.C. Howlett, C.R. Hutchinson,, B.R.W. Hinton. Corrosion of Magnesium Alloy ZE41 The Role of Microstructural Features, Corrosion Science, 51, 2009, pp [4] Walid Khalfaoui, Eric Valerio, Jean-Eric Masse, Michel Autric. Excimer Laser Treatment of ZE41 Magnesium Alloy for Corrosion Resistance and Micro Hardness Improvement. Optics and Laser In Engineering, Elsevier, 48 (9), 2010, pp [5] Kelvii Wei Guo. A Review of Magnesium/Magnesium Alloys Corrosion and its Protection. Recent Patents on Corrosion Science, 2, 2010, pp [6] Nandini Dinodi, A. Nityananda Shetty. Electrochemical Investigation ns on the Corrosion Behaviour of Magnesium Alloy ZE41 in a Combined Medium of Chloride and Sulphate. Journal of Magnesium and alloy, 1, 2013, pp

7 Microstructural Studies of Magnesium ZE41 Rare Earth Alloy using SEM [7] Anthony Gallaccio, William T. Ebihara. Corrosion Susceptibilities of Magnesium Alloys AZ91, EZ33 and ZE41. Technical Report ARSCD-TR-83007, US Army Armament Research and Development Command, [8] Abdel Salam Hamdy and H. M. Hussien. Deposition, Characterization and Electrochemical Properties of Permanganate-Based Coating Treatments over ZE41 Mg-Zn Rare Earth Alloy. International Journal of Electrochemical Science, 8, 2013, pp [9] Mruthunjaya M, K.I.Parashivamurthy and Devappa, Microstructural Characterization and Hot Erosion Behavior of CRC - NICR Coated Steel using HVOF Technique. International Journal of Mechanical Engineering and Technology, 7(3), 2016, pp [10] R. Bhuvaneswari, M. Jagadeesh, E. Ezhilarasi, A. Thangadurai and P. Magudeaswaran, Microstructural Study on High Performance Concrete Made with M Sand. International Journal of Civil Engineering and Technology, 8(3), 2017, pp com