AU2021101683A4 - A process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route - Google Patents

Abstract

The present disclosure relates to a process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route, wherein the aluminum composites (AMCs) are fabricated for various weight percentage selected from 3.5%, 7.0%, 10.5%, 14.0 % and 17.5 % using Al-Mg-Si alloy matrix and the composition in wt% of alloy matrix are 1.0%Mg, 0.6%Si, 0.19%Cr, 0.27%Cu, 0.20 %Fe, 0.15% Mn, 0.15% Ti and Al (balanced). The surface morphology and elemental composition of fabricated composite material were characterized by Scanning Electron Microscope (SEM) and energy dispersive x-ray spectroscopy (EDS) respectively. The boron carbide (B4C) powder is mechanically milled with alloy powder using a ball milling unit for about 2 hours in toluene solution. 20 100 102 Dryingboroncarbide(34C)particlesat400degreeCelsiusforlhour I Fabricatingaluminumcompositesuponhotpressingboroncarbidepowderandalloymatrixusing 104 powder metallurgyroute Figure 1 1' .. .. 0 5 10 15 _ll Scale 7430 cts Cw 0000 Wt% 22.17 37.74 10.99 7.27 4.89 4.60 2.6 4.72 0A7 4.08 0.58 0.04 Figure 2

Description

102 Dryingboroncarbide(34C)particlesat400degreeCelsiusforlhour

I Fabricatingaluminumcompositesuponhotpressingboroncarbidepowderandalloymatrixusing 104 powder metallurgyroute

Figure 1

1' .. ..

0 5 10 15 _ll Scale 7430 cts Cw 0000

Wt% 22.17 37.74 10.99 7.27 4.89 4.60 2.6 4.72 0A7 4.08 0.58 0.04

Figure 2

A process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route

FIELD OF THE INVENTION

The present disclosure relates to a process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route.

BACKGROUND OF THE INVENTION

Recently, more than 1,600 materials have been fabricated in the field of engineering, out of which, more than 200 are listed in the categories of Metal Matrix Composites (MMCs). The MMCs have replaced various alloys used in the automotive and defense industries owing to their attractive properties at very low cost. The Aluminum Matrix Composites (AMCs) are a unique choice for replacing metals and alloys due to their wide range of applications in the automotive industries. The AMCs have unique properties such as superior strength, improved wear resistance and higher strength-to-weight ratio makes them a celebrity. The properties of AMCs depend on reinforcements, volume fraction, interfacial bonding, size of reinforcement, and uniform distribution in the composites. The majority of the AMCs are composed of common reinforcements such as SiC, A1203, TiB2, and MoSi2. However, B4C can be a promising candidate in aluminum composites due to its fascinating properties such as high hardness (>30 GPa), high elastic modulus (~445 GPa), low density (-2.52 g/cm3), a low wear coefficient (-2x10-14 m2/N), high melting point (2500 OC) good chemical stability. These promising properties of AMCs have a wide range of the applications such as wear-resistant parts, lightweight armors, automotive parts, and neutron radiation absorbent. Recently, research groups have used SiC and A1203 as automotive brake rotor materials. However, limited work has been done on B4C based automotive brake rotor materials. The B4C has effective efficient better interfacial bonding and higher hardness along with light density as compare to SiC and A1203.

Furthermore, the B4C hard phase properties are useful for pushing the seizure on the higher load at constant sliding. The AMCs have been fabricated by using various sophisticated techniques such as stir casting, investment casting, powder metallurgy, and friction stir. AMC is fabricated by vacuum pressure casting and found 0.85 % porosity and a small amount of shrinkages in the casting samples. Among them, the powder metallurgy technique (P/M) is the most efficient technique in producing of AMCs components owning to excellent interfacial bonding between ceramic carbides and matrix alloy. Furthermore, the powder metallurgy technique provides a uniform dispersion of particles in the AMCs. Thus, the P/M is an outstanding and effective technique than the rest alternative. The hot-pressed composite shows better relative density than SPS & Pressureless fabricated techniques while the micro-hardness of SPS samples showed significant improvement than the remaining techniques in one of the solutions. The finer-grained boron carbide aluminum composites have lower wear rates than coarse-grained Al matrix on tool-steel disk and were also found that as an increase of boron carbide in the composite, the micro-hardness of the composites increases and wear rate decreases to matrix alloy. The bending strength of SiC/Al composites decreases with the increase of reinforced volume fraction due to improper sintering and acts as a defect in AMCs. Furthermore, the dry sliding wears properties like the coefficient of friction and wear rate varied with increasing load and sliding distance. Further, the aluminum, boron composite showed better wear performance than matrix alloy at an applied load of 20 N. It was observed that the aging and solution heat treatment of the B4C/6061 composite also played a significant role to diminish the wear volume and friction at a constant load of 30 N. Subsequently, the highest wear resistance for 6% B4C/6061 at 49.05 N. The small quantity ofB4C the introduced with B4C/Mg composites exhibit better wear performance at lower load. The highest wear resistance of composite (AMCs) than base material and prepared by the frication stir pressing with three passes in comparison. An effect of sliding distance with respect to a weight loss of composite is that the weight loss increased with the increasing of sliding distance and applied load, and the weight loss decreased with increasing of the reinforcement ratio. The wear and friction behavior of aluminum composite, which was at attached formation of transfer layer on the composite surface during sliding. As we know, the boron carbide-based AMCs show better wear-resistant with less density. However, limited research has been studied on boron carbide aluminum-based composite material for the brake drum/ brake rotors in motorcycles or even in passenger cars.

However, development of materials having high tribological, mechanical strength and corrosion resistance property is of much interest for applications in automobile, defense, and marine industries. Therefore, there exist a need to develop the process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route.

SUMMARY OF THE INVENTION

The present disclosure seeks to provide a process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route. Aluminum composites having different ceramics reinforced particles (3.5 ,7.0,10.5,14.0 and 17.5 wt%) were fabricated to study the dry sliding wear behavior with respect to automobile brake pad material. The surface morphology and elemental composition of fabricated composite material were characterized by Scanning Electron Microscope (SEM) and energy dispersive x-ray spectroscopy (EDS) respectively. Dry sliding wear tests were conducted with respect to i.e. applied loads, sliding distances and reinforcements for the performance analysis of prepared AMCs. Additionally, a technique was employed to improve the corrosion resistance as well as hardness of the composite.

The present disclosure seeks to provide a process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route. The process comprises; drying boron carbide (B4C) particles at 400degree Celsius for 1 hour; and fabricating aluminum composites upon hot pressing boron carbide powder and alloy matrix using powder metallurgy route.

An objective of the present disclosure is to fabricate aluminium, boron carbide (B4C) based aluminium matrix composites (AMCs) using Powder Metallurgy (P/M) route.

Another object of the present disclosure is to drying up the boron carbide (B4C) particles at 400 degree Celsius for 1 hour and hot pressing boron carbide powder and alloy matrix using powder metallurgy route.

Another object of the present disclosure is to mill theB4C powder mechanically with alloy powder using ball milling unit (Retsch: PM-400, HEBM) for about 2 hours in toluene solution. Yet another abject of the present disclosure is to create a sample which is used as Keller's reagent by subjecting the matrix alloy and aluminium composites to coarse for fine grinding with the help of silicon particle grinding paper up to 2000 grade and followed by cleaning with acetone, ethanol and DI water.

To further clarify advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings. BRIEF DESCRIPTION OF FIGURES

Figure 1 illustrates a flow chart of a process for fabricating aluminum, boron carbide based aluminum matrix composites using powder metallurgy route in accordance with an embodiment of the present disclosure;

Figure 2 illustrates scanning electron micrographs (SEM) & EDS spectrums of brake pad materials used as a counter material for wear study in accordance with an embodiment of the present disclosure;

Figure 3 illustrates Scanning electron micrographs of B4C reinforcements & Al-Mg-Si matrix alloy corresponding to the EDS spectrum in accordance with an embodiment of the present disclosure;

Figure 4 illustrates the morphology of boron carbide particles dispersion in the aluminum alloy matrix by the Scanning Electron Micrographs (SEM) respectively in accordance with an embodiment of the present disclosure;

Figure 5 illustrates the relative density of AMCs and matrix alloy in accordance with an embodiment of the present disclosure;

Figure 6 illustrates Micro-Hardness as function of B4C content in accordance with an embodiment of the present disclosure;

Figure 7 illustrates the variation of wear rates in B4C/Al-Mg-Si composites with respect to sliding distance up to 2.5 km at constant load of 20 N in accordance with an embodiment of the present disclosure;

Figure 8 illustrates the effect of wear rates of AMCs which are examined with the variation of applied load under a fixed sliding distance (2.5 km) in accordance with an embodiment of the present disclosure;

Figure 9illustrates Scanning electron micrographs (SEM) showing of worn out surface of B4C/Al-Mg-Si composites with particulate B4C Particles in accordance with the embodiment of the present disclosure;

Figure 10 illustrates friction coefficient of AMCs under variable applied loads of 20N, N and 50N up to a fixed sliding distance (2.5 km) in accordance with an embodiment of the present disclosure

Figure 11 illustrates SEM micrographs of wear debris from worn-out surfaces of Matrix alloy & aluminum composites(AMCs) and EDS of composite debris generated in accordance with an embodiment of the present disclosure;

Figure 12 illustrates electrochemical potentiodynamic polarization curves (Tafel plots) and electrochemical impedance spectroscopy (Nyquist plots) curves of Al-Mg-Si and B4C/Al Mg-Si composites in accordance with an embodiment of the present disclosure;

Figure 13 illustrates the electrochemical potentiodynamic polarization curves (Tafel plots) of the 3.5% B4C/Al-Mg-Si before solution heat treatment and after solution heat treatment, Nyquist plots of the composite before and after solution heat treatment, Variation of Vickers micro hardness after solution heat treatment, and The effect of intermixing respectively in accordance with an embodiment of the present disclosure;

Figure 14 illustrates schematic of Synthetic Process and pin-on-disk dry sliding wear setup in accordance with an embodiment of the present disclosure;

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein. DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

Figure 1 illustrates a flow chart of a process for fabricating aluminum, boron carbide based aluminum matrix composites using powder metallurgy route in accordance with an embodiment of the present disclosure. At the step 102 the process 100 includes, drying boron carbide (B4C) particles at 400degree Celsius for 1 hou. The particle size of the matrix alloy powder and B4Cparticles powder were 20 m and 34 m, respectively. Initially, B4C particles powder was dried up at 400 °C for1 hour. Therefore, theB4C particles powder mechanically milling with alloy powder using ball milling unit (Retsch: PM-400, HEBM) for about 2 hours in toluene solution.

At the step 104 the process 100 includes, fabricating aluminum composites upon hot pressing boron carbide powder and alloy matrix using powder metallurgy route. The aluminum composites (AMCs) % x B4C/Al-Mg-Si composites where x = 3.5%, 7.0%, 10.5%, 14.0 % and 17.5 % were prepared using Al-Mg-Si alloy matrix. The composition in wt% of alloy matrix was used 1.O0%Mg, 0.6%Si, 0.19%Cr, 0.27%Cu, 0.20 %Fe, 0.15% Mn, 0.15% Ti and Al (balanced). The fabricated AMCs reinforced with B4C contents were fabricated by powder metallurgy (P/M) route. Figure 2 illustrates scanning electron micrographs (SEM) &EDS spectrums of brake pad materials used as a counter material for wear study in accordance with an embodiment of the present disclosure. For the counter material analysis, an automobile brake pad material was used as a disc material for the wear study. The brake pad material was consisting of following ingredients (a) Phenolic resin (b) Filler materials (BaSO4) and remaining amount of (c) Metallic chips (e.g. Brass), etc. The figure 2A shows the surface topography of brake pad material which is a composite material of various reinforcements and is characterized by Scanning Electron Microscope (SEM). It is revealed that the figure consists of different color ingredients such as a gray strip (brass chips), the blackish traces show the presence of phenolic resin and some amount of fillers. They are evenly spread on the pad. The figure 2B clearly depicted the following number of elements are (Ba, 0, Fe, Si, Ca, S, K, Cu, Zn, Al, Mg and Mn) confirmed by EDS on the surface of brake material and also tabulated of each element in wt. %. The brake material was properly polished using silicon carbide grit paper up to 1200 and then subsequently cleaned by the wet cotton of ethanol before conducting the wear tests. All the wear tests were carried out at temperature of 28+1 OC and relative humidity of 22±5%.

Figure 3 illustrates Scanning electron micrographs of B4C reinforcements & Al-Mg-Si matrix alloy corresponding to the EDS spectrum in accordance with an embodiment of the present disclosure. The EDS analysis confirms the element present in ceramic particles and also in the matrix alloy which were embedded in the matrix alloy.

Figure 4 illustrates the morphology of boron carbide particles dispersion in the aluminum alloy matrix respectively in accordance with an embodiment of the present disclosure. The percentage of dispersion in figures A B C D & E are (a) 3.5% B4C/Al-Mg-Si (b) 7.0% B4C/Al

Mg-Si (c) 10.5% B4C/Al-Mg-Si (d) 14.0% B4C/Al-Mg-Si (d) 17.5% B4C/Al-Mg-Si respectively. The obtained morphology by the Scanning Electron Micrographs (SEM) is the evidence for the uniformly distributed and properly embedded reinforced (B4C) particles in Al Mg-Si matrix alloy. There is no void appeared at the interface of particles in the AMCs. The micrographs showing that the B4C ceramic particles were uniformly distributed in the AMCs. This can be attributed to centrifugal effect which generates uniformly among the particles during the milling process and afterwards, also proper sintering process ensures them to inter particle bonding. Consequently, it would help to control the microstructure and their mechanical properties. The ceramic reinforced particles are marked and show good bonding between matrix and reinforcement. The samples containing clusters of particles at high reinforced composite also contain some porosity level. Which were attributed to the addition of B4C and it can be attributed to mismatching of shape and size of ceramic reinforced and matrix alloy particles as reported.

Figure 5 illustrates the relative density of AMCs and matrix alloy in accordance with an embodiment of the present disclosure. The mass fraction of B4C content and matrix alloy can be correlated with the weight fraction and densities of composite, matrix and particle content. The theoretical density of the aluminum composites can be calculated from the rule of mixture. While the actual density was measured by Archimedes's principle as per ASTM standard B962-15 using equations.

Relative density = Theoretical density/Experimental density Porosity = 1-Relative density

It is observed that the theoretical density increases with increases of B4C content. The corresponding values of the relative density of AMCs and matrix alloy are tabulated in the table below:

Table - Mechanical properties of AMCs

Reinforcement Experimental Theoretical Relative density Hardness

(wt.%) density, (g/cm 3) density, (g/cm 3) (%) (HV) 0 2.7003 2.6046 0.96456 45.0+2.0 3.5 2.6936 2.5655 0.95244 63.0 2.1 7.0 2.6877 2.545 0.94691 64.0 2.2 10.5 2.6818 2.5245 0.94135 73.0+ 2.1 14.0 2.6761 2.502 0.93494 82.1+2.2 17.5 2.6681 2.4327 0.91177 98.0+2.2

However, the experimental density follows the same trend which meant that the AMCs show some porosity level which increases with an increase ofB4C content in aluminum matrix. The increasing porosity level in aluminum composites is due to intrinsic characteristic of B4C particles which is harder compare to the matrix phase and developed some amount of clustering of particles in high content of reinforcement into composite which is incompressible and would resist during compaction. As a result, firstly the contact area between the particles increases in the composite. Secondly, the thermal coefficient of aluminum (24.Ox10-6 /oC) and B4C (6x10-6 /oC) are different which is result in the behavior of AMCs rapidly changes per oC temperature with respect to ceramics reinforced during sintering process. Therefore, it is expected to enhance the dislocations near to ceramics interface.

Figure 6 illustrates Micro-Hardness as function of B4C content in accordance with an embodiment of the present disclosure. The micro-hardness is calculated with the average of five readings on Vickers hardness testing machine. It is clearly observed that the micro-hardness of AMCs increases with the increasing B4C particles. The hardness of 17.5 weight % B4C and 3.5 weight % B4C in AMCs are calculated as 98 HV and 63 HV respectively, which are 54.15% and 28.76% higher as compared to the Al-Mg-Si alloy matrix (45 HV). The higher hardness of composites is attributed to the following factors: (a) the presence of intrinsic hard phase of boron carbide (B4C); (b) generation of disorders in composite structure due to the incorporation of reinforcement (B4C); (c) dispersion strengthening effect due to uniform distribution of B4C particles; (d) good bonding between reinforcement and matrix alloy.

Figure 7 illustrates the variation of wear rates in B4C/Al-Mg-Si composites with respect to sliding distance up to 2.5 km at constant load of 20 N in accordance with an embodiment of the present disclosure. The wear rates are in (mm3/m) and percentages ofB4C content are 3.5%, 7 %, 10.5%, 14 % and 17.5 %. Wear rates of matrix alloy and AMCs are studied with respect to sliding distance at a constant load (20N) and variable loads. The experiments were conducted up to the total sliding of 2500 m (2.5 Km) under a constant applied load of 20 N in the first slot. It is observed that the wear rates for all the AMCs increase with increasing sliding distance. It is also important to note that the wear rates decrease with increasing of wt.% of B4C content under a constant load. The deceasing wear rate of composites can be attributed to Archard law i.e. the hardness of the samples is directly proportional to the B4C contents. Hence, wear rate of the composites is inversely proportional to the hardness. Additionally, the increased wear rates of composites with increasing sliding distance is due to the following facts: (a) the wear debris generated during sliding of AMCs on counter materials acts as third body which affects the friction force and wear rates; (b) the contact time between surfaces of AMCs and counter materials increases under fixed load and velocity; (iii) activated thermal deformations is also a key factor in this regard. It has been observed that the wear rates of the matrix alloy show high value at a lower sliding distance and after that it decreases up to 2.5 km. This can be attributed to the fact that contact between two surfaces creates sharp asperities and motivate to plastic deformation at their points. During the course of time, they fill the valley of material and become smooth at long distance.

Figure 8 illustrates the effect of wear rates of AMCs which are examined with the variation of applied load under a fixed sliding distance (2.5 km) in accordance with an embodiment of the present disclosure. It was observed that the wear rates of AMCs increases with increasing applied load from 20 to 50 N. It was also notices that the wear rates increase with decreasing of wt.% of B4C content in all load condition. By contrast, high wear rate is observed in Al-matrix alloy and minimum wear rate of AMCs. The increasing wear rate with respect to load can be attributed to following two factors (a) AMCs and brake pad material (counter material) slide each other at higher load, both the surface reaches at higher temperature, the result would reduce protective layer (MML) and B4C reinforced helps for strengthening to soft alloy (b) due to higher temperature, the plastic deformation occurs therefore, drastically wear rate occurs which leads to the adhesion wear, B4C particles formed to B203 layer. It has found that the boron oxide layer delaminated at low velocity and higher load.

Figure 9 illustrates Scanning electron micrographs (SEM) showing of worn out surface of B4C/Al-Mg-Si composites with particulate B4C Particles in accordance with the embodiment of the present disclosure, Wherein the weight percentages of the B4C/Al-Mg-Si composites are 3.5, 7.0, 10.5, 14.0 and 17.5 % respectively. These are the evidence of morphology change to AMCs at higher load. This furrow can be explained on the basis of high load, when load was applied to the material, loads was uniformly distributing on the contacting surfaces and effective area. As a result, the surface morphology changes from blunt to smooth during sliding. It may be attributed due to the plastic deformation and Archard's law, the wear rate increase as the hardness of material decreased. It was also noticed that the irregular delamination regions generally occur with perpendicular direction to the sliding distance. The deform regions are occurring due to the removal of materials in the form of debris which has been discussed further in details. The matrix alloy was showing abrasive mode of wear as the number of furrows with deep ridges on the surface It is observed that the matrix alloy showing heavier damaged as compare to AMC under the same applied condition.

Figure 10 illustrates friction coefficient of AMCs under variable applied loads of 20N, N and 50N up to a fixed sliding distance (2.5 km) in accordance with an embodiment of the present disclosure. The graphs show that the sharply increase at the initial stage and reach to the maximum value and exhibit the steady state behavior. All the curves follow the same trend, the friction coefficients reaching maxima after the 250 m sliding distance. The variation of the friction coefficient is in the range of 0.22 to 0.42. Further, it was also found that the coefficients of friction of AMCs at steady state are relatively lower as compared to matrix alloy. The variations in the coefficient of the friction are attributed to the following reasons: In the initial stage, when two surfaces come together and start sliding, a friction force is generated. This prevents the motion which causes both surfaces to be blunt or fractured under applied load. However, with increasing sliding distance, these surfaces become smoother during continuous sliding and the coefficient of friction reaches to steady state condition. Our results are in accordance with the previous report result, where similar behavior of retardation of friction coefficients against brake pad materials (counter materials) was observed. This can be explained by the formation a boron oxide on the surface during dry sliding. Furthermore, the reduction of contact area due to the incorporation of B4C may be accountable to lower the friction coefficients during wear

Figurell illustrates the SEM micrographs of wear debris from worn-out surfaces of Matrix alloy & aluminum composites (AMCs) and EDS of composite debris generated in accordance with an embodiment of the present disclosure; It has been observed that the shape and size of the small and large flakes generated from Al-matrix alloy due to repeated loading condition. The size of the flakes is varying between 15 to 50 m. The whole surface appears smooth and irregular with small flakes which come out in a layer. It can be attributed due to plastic deformation at higher loading and also another possibility in such way, when AMC and brake pad material are sliding each other, any material may get removed from the grooves and gets collected at the tip of asperity. Thus leading to wedge formation and has reported. Further, the worn surface of the AMC (17.5 % B4C/Al-Mg-Si) shows smoother and fine furrow and also limited plastic deformation occurs as compare to matrix alloy at the same condition. Therefore, the smooth worn surfaces of composite showed better performance i.e. higher wear resistance. The high wear resistance of AMC may be attributed to the following reasons (i) Higher hardness with intrinsic property B4C as a load bearing capacity and (ii) formation MML between AMC and counter surface protects Surface. The morphology of worn debris of AMC has gradually been changed at the higher load with low Speed. Here, the formation of spherical debris may be possibly due to the adhesive and along with the reaction product as a lubricant layer between AMC and counter surface. The adhesive wear generally occurs when the pin and counter surface is in sliding contact with any lubricant layer. The contact was occurring on the asperity at the interface and shared by the relative movements. Therefore, the detachment of fragments comes out in the form of protective debris which brings out the separation of both the surface, but in reversely, some of the debris fracture occurs by a fatigue process during cyclic loading and unloading actions. The similar behavior has been found by EDS analysis. The debris shows the traces of pad constituents and higher percentage of Fe contents with high load.

Figure12 illustrates electrochemical potentiodynamic polarization curves (Tafel plots) and electrochemical impedance spectroscopy (Nyquist plots) curves of Al-Mg-Si and B4C/Al Mg-Si composites in accordance with an embodiment of the present disclosure. The B4C/Al Mg-Si composites are of 3.5%, 7.0% and 10.5%. The corrosion current density (Icorr) and corresponding corrosion potential (Ecorr) were derived as the intersection point of the lines obtained by extrapolation of the cathodic and the anodic branches of the Tafel plot.

Where, Pa and Pc are the Tafel slopes of the anodic and cathodic reactions. The calculated corrosion parameters are presented in the given Table.

Table: Electrochemical corrosion parameters of Al-Mg-Si and B4C/Al-Mg-Si composites. Composite Ecorr Icorr Be Ba Ret Rp (V) (nA/cm 2) (mV/dec) (mV/dec) (4) (t2.cm 2

) Al-Mg-Si -0.955 1.7 364.5 237.5 9.9 x 101 37.2x 106

3.5 %

B4C/Al-Mg-Si -0.869 6.2 288.8 177.1 1.8 x 10' 7.7 x 106 7.00% B4C/Al-Mg-Si -0.828 13.7 393.8 249.4 1.3 x 10' 4.8x 106 10.5% B4C/Al-Mg-Si -0.782 14.3 423.0 233.0 1.1 x 101 4.5 x 106

Compared to the unreinforced Al-Mg-Si, it is seen that B4C/Al-Mg-Si composites show high Icorr and low Rp, and the value of Icorr increases (while Rp decreases) with the increase of B4C Content in the composite conclusively, results show that corrosion resistance of B4C/Al Mg-Si composites decreases with the increase of B4C.The data of EIS (Nyquist plot) can be explained by Raddle+Warburg circuit model. The circuit includes a resistor due to solution resistance (Rs), a charge transfers resistor (Rct) due to the faradic charge transfer between metal and the solution (measure of metal corrosion), a Warburg element (W) that associates the diffusion process, and a constant phase element (CPE) which accounts for the electrical double layer at the liquid/metal interface. The diameter of the semicircle extrapolated in the Nyquist plot represents the charge transfer resistance, Rct in high frequency region on Z' axis (real axis). Larger the diameter of the semicircle more will be the corrosion resistance of the metal. The findings show that Rct decreases with increase of B4C content in the B4C/Al-Mg-Si composites, showing the reduction of corrosion resistance due to the incorporation of B4C. The data of EIS supports the data of potentiodynamic polarization measurements. The Reason of corrosion in B4C/Al-Mg-Si composites may be understood as follows. The presence of pores around the B4C particles increase the permeability of corrosive ions to interact with the Al matrix, that causes the enhanced charge transfer between the metal and electrolyte ions, showing the low Rct (smaller diameter semicircle) in the Nyquist plot. Thus, porosity generated due to the incorporation of B4C particles increases the corrosion reaction in the composite material. Furthermore, B4C/Al Mg-Si composites have two electrochemically dissimilar materials; galvanic corrosion may also be responsible to degrade the corrosion resistance of the composites. Evidence of structural defects (change in crystallite size and strain) in B4C/Al-Mg-Al composites are well supported by the XRD data.

Figure 13 illustrates the electrochemical potentiodynamic polarization curves (Tafel plots) of the 3.5% B4C/Al-Mg-Si before solution heat treatment and after solution heat treatment, Nyquist plots of the composite before and after solution heat treatment, Variation of Vickers micro hardness after solution heat treatment, and The effect of intermixing respectively in accordance with an embodiment of the present disclosure. Corrosion of B4C/Al-Mg-Si composites is a problematic issue that has to be overcome for the application of the composites as long-lasting materials in marine industries. To improve its corrosion resistance, a strategy of solution heat treatment (SHT) is employed. 3.5% B4C/Al-Mg-Si composite is used for the experiment. The solution heat treatment was carried out at 500°C for 120 minutes in a tubular furnace (heating rate 15oC/min) and subsequently cold water quenching was done to retain the solute atoms in the solid solution treatment. The Icorr of the composite is obtained, after SHT to be 2.5 nA/cm2 that is around half of that (Icorr = 6.2 nA/cm2) of the composite SHT, showing that SHT of the composite improves its corrosion resistance. The composite after SHT shows Rct of 2.5 x 105 Q that is higher than the Rct (1.8 x105 Q) of the as-received composite. The results of ElSare consistent with the results of potentiodynamic polarization measurements (Tafel plots).

To understand the mechanism of the improved corrosion and hardness, the optical microscopy images of the composite after SHT is also investigated. The prime reason behind the improved corrosion resistance can be explained on the basis of eutectic or paratactic phase. The system (3.5% B4C/Al-Mg-Si composite) does not show complete solid solubility, and the solute usually soluble at certain limit is known as solubility limit of the system. The solid solubility depends on temperature, and the temperature decreases with deceasing solid solubility along the solvus line. The solvus line is the boundaries between solid solubility and intermetallic precipitates. The solid solubility of all the alloying element usually intermixing in the Al-Mg-Si matrix at higher temperature ranging from370 to 500 oC.Thus,the solution heat treatment is the effective tool to improve the corrosion resistance of the B4C/Al-Mg-Si composites. The intermixing effect makes the surface more homogeneous with reduced defects, leading it less susceptible to corrosion. In addition to the improved corrosion resistance, the composite after SHT also exhibits the improved (around two times) hardness of 108.1 5.3HV. The possible mechanism of the improved hardness of the composite after SHT can be discussed as follows. Strain field around the B4C particles are caused by the differential thermal expansion of the particles and the matrix during the quenching in the SHT process. As such, the greater degree of supersaturating during SHT might be responsible for the enhanced hardness of the composite.

Figure 14 illustrates schematic of Synthetic Process and pin-on-disk dry sliding wear setup in accordance with an embodiment of the present disclosure. The aluminum composites (AMCs) % x B4C/Al-Mg-Si composites where x = 3.5%,7.0%,10.5%,14.0 % and 17.5 % were prepared using Al-Mg-Si alloy matrix. The composition in wt% of alloy matrix was used 1.0%Mg, 0.6%Si, 0.19%Cr, 0.27%Cu, 0.20 %Fe, 0.15% Mn, 0.15% Ti and Al (balanced). The fabricated AMCs reinforced with B4C contents were fabricated by powder metallurgy (P/M) route. The particle size of the matrix alloy powder and B4C particles powder were 20 m and 34 pLm, respectively. Initially, B4C particles powder was dried (at 400 °C for 1 hour). Therefore, the B4C particles powder mechanically milling with alloy powder using ball milling unit (Retsch: PM-400, HEBM) for about 2 hours in toluene solution. The matrix alloy and all aluminum composites (B4C/Al-Mg-Si composites) were subjected to coarse to fine grinding with the help of silicon particle grinding papers up-to 2000 grade followed by cleaning with acetone, ethanol and DI water. Therefore, the samples were used as Keller's reagent (95 ml water, 2.5 ml HNO3,

1.5 ml HCl, 1.0 ml HF) for investigating the microstructure surface morphology by using scanning electron microscope (SEM) of the Model: ZEISS EVO 18 with an inbuilt Energy Dispersive Spectroscopy (EDS) morphology and elemental analysis of B4C/AlMg-Si composites were examined before and after the dry sliding wear tests at room temperature. The densities of all the AMCs samples were determined by using Shimadzu analytical balance (AUX-220) with the solid gravity measurement kit (SMK-401). The measurements of Hardness tests were conducted by using Micro-Vickers hardness equipment (Model: Simandzu HMV 2.0) for 20 s of dwell time under applied load of 1000 gf. The wear tests were performed using pin-on-disc (Model: DUCOM TR-20 PHM-400) testing machine and schematic of pin-on-disk dry sliding wear set up. The disc material was considered as a brake pad material, and the AMCs cylindrical shape samples chosen with the dimension (10 mm diameter and 20 mm length). All the wear tests were carried out at a sliding speed of 0.61 m/s for sliding distance of 2500 m (2.5 km) under various loads (20 N, 35 N and 50 N).

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims (9)

WE CLAIM

1. A process for fabricating aluminum, boron carbide-based aluminum matrix composites using powder metallurgy route, the process comprises:

drying boron carbide (B4C) particles at 400degree Celsius for 1 hour; and fabricating aluminum composites upon hot pressing boron carbide powder and alloy matrix using powder metallurgy route;

2. The process as claimed in claim 1, wherein the aluminum composites (AMCs) are fabricated for various weight percentages selected from 3.5%, 7.0%, 10.5%, 14.0 % and 17.5

% using Al-Mg-Si alloy matrix.

3. The process as claimed in claim 1, wherein the composition in wt% of alloy matrix are 1.O0%Mg, 0.6%Si, 0.19%Cr, 0.27%Cu, 0.20 %Fe, 0.15% Mn, 0.15% Ti and Al (balanced).

4. The process as claimed in claim 1, wherein the boron carbide (B4C)powder is mechanically milled with alloy powder using a ball milling unit for about 2 hours in toluene solution.

5. The process as claimed in claim 4, wherein the ball-to-powder ratio of the ball milling unit is (6:1) and rotation speed is about 200 rpm under inert (Ar) environment during milling of boron carbide.

6. The process as claimed in claim 1, wherein investigating microstructure surface morphology of the aluminum composites comprises:

subjecting matrix alloy and all aluminum composites (B4C/Al-Mg-Si composites) to coarse to fine grinding with the help of silicon particle grinding papers up-to 2000 grade followed by cleaning with acetone ethanol and DI water; and using the samples as Keller's reagent (95 ml water, 2.5 ml HNO3, 1.5 ml HCl, 1.0 ml HF) for investigating the microstructure surface morphology by using scanning electron microscope (SEM) of the model.

7. The process as claimed in claim 1, wherein a solution heat treatment (SHT) is employed to improve corrosion resistance of the B4C/Al-Mg-Si composite, wherein the solution heat treatment is carried out at 500degree Celsius for 120 minutes in a tubular furnace (heating rate °C /min) and subsequently cold-water quenching is performed to retain the solute atoms in the solid solution treatment.

8. The process as claimed in claim 1, wherein a linear regression model is used to optimize the control factors of the boron carbide-based aluminum matrix composites, wherein control factors selected from a group of factors are sliding distance, applied load and reinforcements.

9. The process as claimed in claim 1, wherein hot pressing of boron carbide powder and alloy matrix is performed by a hot pressing unit (die pressing) by applying heat ranging from 900 °F (480 °C) to 2250 °F (1230 °C).