Microstructure and Phase Analysis of Al-Based Metal Matrix Composite

International Journal of Advanced Engineering

Manuscript received: January 3, 2021; Revised: February 3, 2021; Accepted: February 6, 2021

Corresponding Author : Anu Shrestha

Author’s affiliation: Dept. of Mechanical Engineering, IoE, Purwanchal Campus, Dharan, Nepal Email: [email protected]

Copyright © ICT-AES

Microstructure and Phase Analysis of Al-Based Metal Matrix Composite

Department of Mechanical Engineering, Institute of Engineering, Purwanchal Campus, Dharan, Nepal [email protected]

Abstract

In this paper, microstructure and phase analyses were used to determine the characteristics of coating layers which was Al-based metal matrix composite in -situ. For this work high power laser (2kWFiber laser) was used to scan preplaced powder. The microstructure and phase analysis were carried out by using electron scanning microscope (SEM) with EDX (Energy Dispersive X-ray) spectrography / Energy Dispersive spectroscopy (EDS) and XRD (x-ray diffraction) to evaluate the micrograph of location and distribution of elements, dispersive of particles, holes, and cracks in coating layer.

Keywords: Laser cladding, MMC, SEM, EDX/EDS and XRD.

1.

Introduction

The material selection of any product depends upon the properties of materials. Now-a-days, surface modification technology is widely used to produce composite materials. After making composite materials the evaluation of surfaces was done by Microstructure and phase analysis of Metal Matrix Composite (MMC) which was formed by laser cladding. The microstructure and phase analysis of materials play vital role to detect elemental distributions, defects and phases of the subtract material [1].

A scanning electron microscope (SEM)) was used for surface morphology, composition of the sample and Energy Dispersive Spectroscopy/Energy Dispersive X-ray (EDS or EDX) analysis was used for elemental identification and quantitative compositional analysis (characteristics of material structures). XRD pattern was used for phase identification of the sample [2].

2. Methods of Preparation of Samples

2.1 Cutting of Sample

Whenever, we cut the sample, we consider the micro-cutting. The subtract material of Al was cut by band saw of size 30 x 30 x 15 mm and before cladding the substrate, we clean with acetone in an ultrasonic bath and dried in a hot air.

2.2 Pre-placing powder mixture on the substrate material

In this process, Cuo, Al and sio2 powders were mixed with acetone and preplaced on the substrate material by

K-coater machine. The thickness of pre-placed powder were 250µm ,400µm and 500µm.

.

2.3 Cladding

The laser cladding is a laser surfacing technique that involves the deposition of materials with supreme properties on substrate. Cladding was done by re-melting preplaced powder with high power 2kW fiber laser and formed Al base metal matrix composite (MMC) [3].

2.4 Mounting

Ultrasonic cleaning was done on the samples before mounting. The samples were cold mounted for protecting their edges and easy handling for small samples during grinding and polishing. In this process, the samples were placed in the molds and the mounting powder of synthetic resin(epoxy) was filled and hardening chemical was poured in the molds. The embedded samples were formed after exothermic reaction between the molding powder and hardening chemical in the molds. After half an hour, the mounted samples were taken from the molds by pressing in the press machine [4].

2.5 Grinding

The samples were ground to produce fine surface on grinder/polishing machine. Initially rough grinding was performed to remove irregular surfaces and fine grinding was done to produce flat and smooth surface. After grinding, the samples were re-ground on Grinder and Polishing machine by using abrasive papers of SiC, grit sizes of 250 µm,350 µm and 650 µm respectively.

2.6 Polishing

This process was used to remove the damaged introduced by previous operations. Polishing was carried out on Grinder/polishing machine. During diamond polishing, fine grains of diamond and lubricant were applied on polishing cloth and the samples were pressed with minimum force on the rotating polishing cloth which was mounted on the rotary table of the grinder/polishing machine [5]

2.7 Chemical Etching

The samples were polished and ultrasonically cleaned and etched by Keller’s reagent (2.5ml HNO3: 1.5ml

HCl: 1ml HF: 95% ml water) to remove Al parts and highlight reinforcement. The samples were immersed in Keller’s reagent for one minute and washed with distilled water and dried under the hot air. The samples were observed by using an optical microscope with 100X magnification to decide if the polishing was enough or not.

Grain boundaries, different brightness and shape of grains were observed on the sample. The microstructure and phase analysis were carried out by using electron scanning microscope (SEM) with EDX (Energy Dispersive X-ray) spectrograph /Energy Dispersive spectroscopy (EDS) and XRD (x-ray diffraction) to evaluate the micrograph of location and distribution of elements, dispersive of particles, holes, cracks in coating layer.

3.

Microstructure Analysis

The samples were polished and ultrasonically cleaned and etched by Keller’s reagent (2.5ml HNO3: 1.5ml HCl :1ml HF: 95% ml water) to remove Al parts and highlight reinforcement particles. Fig.1(a) shows the microstructure of cross section of coating surfaces produced with the laser power1000W, scanning speed 1500 mm/min, hatching distance 1 mm, focal distance (Z) = -325 mm, laser gas pressure 0.5 bar, angle of nozzle –00 and powder with cellulose acetate 5% respectively.

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Figure 1. (a) Scanning Electron Microscope (SEM) micrograph of the transverse cross section of the coatings deposited at scan speed 1500mm/s, hatching distance 1 mm and laser power 1000W of B3 sample and (b) SEM picture of sample A15 showing different layers (A-Cladding layer and B-Interface layer).

In Figure 1(a), different dispersive particles were identified in the coating layer and a firm coating layer of thickness about 30 microns was captured in Figure 1(b). From the Figures 1, it is cleared that an effective layer coating was formed due to laser cladding processing and coating layer was made by some dispersive particles.

B A

Figure 2. Surface morphology of the top surface of the coated layer

Figure 3. Micrograph of line EDX spectroscopy in cross section of a coated sample A7 (A coating layer, B-interfacing zone, C-substrate material and X direction- shows the direction of line scanning; Y direction- shows the variation of elemental compositions)

Micro holes, micro- cracks were observed on the top surfaces of the coating layer. The surface morphology of top surface of the coating as capture by SEM in secondary electron beam mode has been shown in Figure 2. Hence, it is cleared that the produced coating layer is not smooth; having micro- cracks and holes/cavity which may be generated due to the escape of entrapped gases from the surface.

Line EDX (Energy Dispersive X-ray) spectroscopy was done at the cross section of the samples an ample micrograph has been identified and shown in figure 3 to distinguish the variation of elements of the coating layer.

Figure 4. Energy dispersion spectroscopy of sample A38

Figure 5. X-ray elemental mapping of Al, Cu, O of sample 38

From the line scanning of EDX spectroscopy (figure 3); it is clear that the elementals of coating layer was

Elements Weight% Atomic% O K 53.10 65.63 Al K 46.90 34.37 Si K 0.00 0.00 Cu K 0.00 0.00

reach in aluminum (Al) and oxygen (O). The elemental composition of the coating layer may be the reach in aluminum oxides. The copper (Cu) took place at the interface layer may enhance good bonding between coating and substrate.

Energy Dispersive Spectroscopy (EDS) elemental mapping for the top portion of the transverse cross section (in Figure 4) shows more elements Al and oxygen as a darker area. So it could be concluded that the reinforced Al2O3 phase are larger than other phases. Similarly, according to bulk EDS on interface zone of sample B3 shows

the distributions of different elements such as Al, Si, Cu and oxygen. SEM and EDS showed that it is the Al- MMC, because there is a large amount of Al. From the elemental mapping of EDS microscopy, it has been showing the probability of presence of aluminum oxide at the coating layer.

4.

Microstructure identification

Figure 6 shows the microstructure of the clad layer formed after the thermite reaction of mixture of CuO, Al and SiO2 powders. According to point EDS of the transverse cross section of sample A15, it was found that the

darker and lighter regions showed significant difference in Al and O composition. The sample A15was scanned in transverse direction and found distribution of elements varies in different regions in laser cladded surface.

Figure 6. (a) SEM micrograph of transverse cross section of the coating showing distinct phases and (b) Fiber like phases dispersed uniformly throughout the matrix

5.

Phase Composition

The phases in the composite Al2O3 have been able to fabricate in situ from different proportion(wt.%) mixture of Al,SiO2 and CuO alloy. The formation of



respect to laser process parameters and the proportions (Wt.%) of powders.

The hardness values growth of the composite material in respect to the matrix material was revealed as a result of hardness tests of the Al2O3 reinforced Al-MMCs. It was observed during metallographic examinations of

composite materials that the Al2O3 phase is distributed in the matrix. According to the X-ray qualitative phase

analysis of the composite material with Al2O3 reinforced aluminum alloy matrix reinforced with Al2O3 (Fig.7).

Other phases also were detected in the investigated composite material. Metallographic examinations on the light and scanning microscopes revealed the homogeneous distribution of the Al2O3 particles in the matrix material.

Figure7. Phase analysis of the sample

6.

Conclusion

Formation of Al-MMC coating withAl2O3 cladding on Al subtract material was performed by mixing Al,

CuO and SiO2 powders to investigate microstructure and phase analyses SEM picture of the sample showed the layer of the thickness of the cladding, interface layer and surface morphology of the top surface morphology of coated layer. Micrograph of line EDX showed the variation of elemental composition. X-ray showed the elemental mapping of Al,Cu,Si and O of the samples.SEM and EDS showed that it was the Al-MMC because there was a large amount of Al. From that it had been showing the probability of the presence of Al2O3. From

XRD pattern phase analysis was performed and found that the composite of Al2O3.Thus the phases in the

composite Al2O3 have been able to fabricate in in-situ from different proportion of Wt (%) mixture of Al, SiO2

and CuO alloy. From microstructure analysis and phase analysis the elemental distribution, properties of clad layer were successfully analyzed which is very important in research work.

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