Tribological, Thermal and Corrosive behaviour of aluminium alloy 2219 reinforced by Si3N4 nanosized powder

The MMC technique is the most effective contrast method when compared with other techniques. By using the method of high energy stir casting, Aluminium alloy Al2219 is reinforced with various percentages of Si3N4 (0, 3, 6, and 9%) particles. X-ray diffraction along with Scanning electron microscope was performed to characterize the composite. The mechanical and thermal behaviours such as differential thermal analysis thermo gravimetric analysis/, tensile , wear and hardness behaviours were investigated. By using electro chemical potentiodynamic polarization test, the consequence of heat treatment on the corrosion behaviour of the composites when compared to its matrix in 3.5 % NaCl when at 600 rpm was also investigated. In this experimental study, the wear of the aluminium composites was signicantly decreased on addition of Si3N4 particles. The study also revealed that, since the inclusion of Si3N4 in the samples and compared to the base aluminium alloy, the mechanical properties of the composites, such as wear resistance , hardness and tensile strength increased by percentage. The surface morphology and Scanning electron microscope analysis of worn surfaces in the test pieces unfold that with the increase in reinforcement content, wear rate decreases.


Introduction
In the recent times, the technology space in aircraft, aerospace, and automotive industries is rapidly advancing which in turn increases the demand for composite materials which is widely being used in the above-mentioned areas. The special properties of Composites materials such as low speci c gravity makes the material highly superior in modulus and strength when compared with most traditional engineering metallic materials [1].
Metal matrix composites are explicitly utilized composite materials which is made with generally wo constituents, one of the constituents is a metal matrix and the other material is a reinforcement. In all the cases, the matrix is outlines with a metal and the use of pure metal as a matrix is mostly avoided. In general, the matrix is constituted by the use of an alloy. The general synthesis of the composite involves the mixing of the matrix and the reinforcement together.
Aluminium is extensively used in matrix material composites (MMCs). This is main reason for this is the unique features of aluminium such as good mechanical properties, low density, good machinability properties, low electrical resistance, high strength and good corrosion resistance. Although comparatively substandard wear resistance of these alloy has restrained its use in speci c tribological applications. In the recent studies, both particulate and bre reinforced aluminium alloy composites fabricated have shown appreciable improvement in their tribological properties, including but not limiting to sliding wear, seizure resistance, friction, and abrasive wear [3]. The production and utilization of Si 3 N 4 was stimulated by increasing demand for low-cost reinforcement [9].
Wear based damages to the material is an important aspect in tribology buy even though it is highly important, it is one of the least understood eld. It is also a youngest topic, lubrication, friction and wear Page 3/22 which needs more scienti c attention. The practical signi cance of the same is being identi ed through the years [15].
Wear is responsible for a huge annual outlay by the consumers as well as the industries. Most of this goes in replacing or repairing equipment's that is worn out and does no longer perform its function. [7]. In many parts of the machine the damage is seen only after a percentage of the entire volume of the part has worn out. [14].
Number of studies have been conducted to characterize tribological behavior of Aluminium-based MMC.
Suresh and Sridhara [16] reported on the impact of Gr and SiC (up to 10% wt%) on the wear properties of LM25-based aluminium composites. It was discovered that increasing the weight fraction of reinforcement particle in MMC reduced wear until it reached 7%, after which it increased. Wear of matrix material composites increased with increasing load due to an unstable tribo-layer, but decreased with increasing speed due to the presence of MML [17]. The effect of SiC and B 4 C on the wear e ciency of the Al7075-based MMC was studied by Uvaraja and Natarajan [29]. Wear rate was found to decrease as the volume fraction of reinforcement, speed, and time increased, whereas it increased as the applied load increased. The reinforcement content was found to be the most important factor, followed by the applied load and sliding speed. Surface morphology and SEM analysis of the test pieces' worn surfaces showed that the wear rate decreased as the reinforcement material increased. The EDS ndings were used to classify the MML that forms on the test specimen's worn surfaces. [17] [22] The effects of reinforcement on composite corrosion activity are still unknown. It has been found that in the presence of reinforcement, the corrosion current density rises, decreases, or remains unchanged. Furthermore, reinforcement has been shown to in uence the open circuit potential (OCP) by increasing, decreasing, or having no effect [24]. Heat treatment results are discovered to be a crucial factor in evaluating the corrosion behaviour of aluminium alloy composites. Kolman and Butt [25] examined the corrosion properties of an aluminum-silicon alloy composite reinforced with in-situ TiB 2 particulate after heat treatment. It was discovered that as the amount of TiB 2 in these composites increased, their corrosion resistance decreased. The effect of heat treatment of the reinforcing BN, Al 2 O 3 , and Ti (C, N) particles in the EN AW-AlCu4Mg1(A) aluminium alloy on its corrosion resistance in the presence of NaCl water solution was investigated by Wodarczyk-Fligier et al. [27]. The corrosion resistance of composite material heat treated in a 3 percent NaCl solution was found to be noticeably improved.
In the frame of reference of the discussion above, the aim of the current investigation is to study the morphological, mechanical and metallurgical properties of Si 3 N 4 reinforced Aluminium Alloy AA2219.
The reinforcement is embeded by high energy stir casting method with various percentage of Si 3 N 4 (0,3,6 and 9) particles. The structural characterization was carried out by SEM, XRD and tests. Tensile, hardness and corrosion test are carried out for determining the mechanical behaviour of this material. TGA analysis has been carried out as thermal analysis. The wear behaviour of AA2219/ Si 3 N 4 MMC has not been explored so far and they are fabricated by two-step stir casting method. Characterization of microstructure and worn surface morphology of the composites was done by Scanning electron microscope (SEM). Tensile fractured samples were made to undergo fractography study. Mechanically mixed layer (MML) of the test specimens were evaluated by EDS.

Experimental Aspects
Casting process In this study the electrical furnace setup was replaced with a stir set up by using a simple blower furnace and the vertical drilling machine assembly as shown in the Fig. 1. As the high operating cost of electrical furnace is annihilated, the variable speed of drilling machine is obtained using the stirrer. The addition of Si 3 N 4 particles in terms of ratio was done at 0, 3, 6, and 9% by the overall weight. Formulation process begins with the stirring out in a graphite crucible in a coal-red furnace. Ceaseless stirring of the molten metal-matrix gives homogeneous mixture of the composite. This is instantly poured into the mould to get solidi ed. For melting the alloy Coal was used as a fuel. Al2219 was kept in a crucible and lique ed by melting it in a blower furnace at a temperature of 670°C for 15 min. The Si 3 N 4 powder was preheated to a temperature of 670°C using a separate mu e furnace. The temperature of the furnace was rst increased above the temperature of the liquid.
Ductile test examples were made according to the ASTM standard and tried in a Universal Testing Machine. In request to gauge the rigidity of the examples, they were made in a round and hollow shape as per ASTM E8. The information estimations of the four examples acquired from the ductile test were utilized. The fortifying stage in the metal network composites bears a huge division of the worry as it is commonly a lot stiffer than the grid. The molecule joining brings about an expansion in the work solidifying of the material. The higher work solidifying rate saw in the composites is because of the mathematical imperatives forced by the presence of the support. The expanding weight % of Si 3 N 4 builds the work solidifying rate. The tensile samples before and after test is shown in gure 2 (a) and (b).

Hardness test.
The composites materials hardness was estimated by utilizing a Brinell hardness machine following the ASTM E10 standard. All the examples were applying a heap of 500 to 3000kgf for a time of Ten seconds. The test was done at room temperature and the estimation of hardness was taken at 3 distinct areas to keep away from the conceivable impact of indenter laying on the hard support particles. The midpoints of the apparent multitude of four readings were accounted for.
Pin-on-disc experimental set up A pin-on-disc equipment is used to carry out the experiment which is coupled with a wear monitor and type friction with a data acquisition system. The above setup is used in measuring the wear behavior of composite by testing it against the hardened ground steel disc (EN-24) which is has a hardness value of 65HRC and surface roughness (Ra) of 0.5µm. the equipment is highly versatile which is designed in such a way to study the wear characteristics only under sliding conditions. In the equipment, sliding usually occurs between the rotating disc and the stationary pin. A D.C motor was used to rotate the disc; the motor is having a speed range of 100-1500 rpm with wear track diameter (50mm*160mm), which would yield sliding speed 0 to 10m/sec. The load has to be applied on pin sample (specimen) by deadweight through a pulley string arrangement. The system's maximum loading capacity is 100N . Fig 3 (a) & (b) shows Wear specimens before and after test.
TGA Differential thermal analysis (DTA) and thermogravimetric analysis (TG) were carried out simultaneously using a TG/DTA EXSTAR 6300 instrument (SII Nanotechnology Inc.). Approximately 10 mg of the specimen is weighed on the alumina crucible and heated from 30 to 800 ℃ in a ow of air atmosphere (100 ml/min). The heating rate was 10 ℃/min. α-Alumina was used as reference standard.
XRD XRD is commonly utilized to assess the samples' purity, phase and crystal structure [24]. Phase analysis of prepared specimens was done by XRD model D2 PHASER (Bruker AXS) using Cu/Kα radiation (λ = 1.54060 Å). Over the 2θ range of 20º-80º with a step size of 0.02º, peak values were obtained. All four samples have signi cant diffraction peaks that could be attributed to the Cu and W structures.
Characteristics peaks has been observed in the XRD pattern, and the relative intensity rate corresponding to the samples.

Corrosive test
Corrosion measurement were carried out using CHI 604D Electrochemical Workstation (CH Instruments, Inc) in 3.5% NaCl Solution using an Ag/AgCl reference electrode and platinum wire as a counter electrode.
The Inhibitive e ciency is calculated using the below equation.
In the above equation for Inhibition E ciency, C ra denotes the corrosion rate of the unreinforced Al2219 alloy and C rs is used to denote the corrosion rate of Al2219 alloy reinforced with Si 3 N 4 . Each run's output consists of a polarisation curve from which the corrosion parameters can be calculated using a manufactured software package using the Tafel  The tensile tested specimen of AA2219 alloy with 0%, 3%, 6% and 9% of Si 3 N 4 reinforced composite is subjected to fracture morphology and the result is as shown in Fig. 6 (i-iv). It has been noted that sample with 3% wt demonstrated a high breakage point. Scanning electron microscope image of AA2219 alloy in the Fig. 6 Figure 10 (a) shows that some of the regions are damaged as seen in as cast Al2219 alloy. When higher load was applied, the degree of grooves formed at the worn surface of the matrix alloy is quite larger which causes a severe plastic deformation which causes severe wear in the specimens.  :   Fig-11(a) shows the X-ray patterns of extracted AA2219 as cast composites. The fabricated AA 2219's Xray diffraction pattern. The presence of aluminium (Al) and copper (Cu) of metallic compounds was discovered through the study of XRD peaks. The diffraction pattern clearly indicates Si 3 N 4 particles, as shown in Fig. 11(b, c, and d). The relative fractions of the strength of the Si 3 N 4 particles were measured.

XRD Investigations
The relative fractions of Si 3 N 4 particles found strength in the XRD pattern, with the highest peak occurring at the reinforcement particles. The particle peaks within the composite are visible using XRD. As the number of Si 3 N 4 particles increases, the probability of reinforcement agglomeration in the AA 2219 matrix increases. The results show that metallic elements are present in the highest peaks and reinforcement is present in the lowest peaks. The relative strength occurs at a 38-degree angle, with strong peaks for wt% of composites. The percentage of Si 3 N 4 in composites has been found to increase, resulting in a higher peak intensity level in the study.

TGA Analysis
Analyzing the thermal response of unreinforced Al2219 and developed Al2219-Si 3 N 4 composites as shown in Figure 12 (a-d), has been established using a differential thermal analyzer (DTA) and thermogravimetric analyzer (TGA). The results from the thermograms shows that as the composite with incorporated Si 3 N 4 has enhances the thermal stability of the aluminium alloy matrix. Apart from increase in inhibition e ciency, the addition of the nanoceramic Si 3 N 4 also causes a decrease in the mass loss as the composite is heated from 30 ℃ to 800 ℃, which is clearly evident from the TG/DTA result. From the graph, there was a 7.3 % loss of mass for the unreinforced Al2219, whereas the addition of the incorporation of Si 3 N 4 decreased the mass loss to 2.5% in 3 wt% Si 3 N 4 reinforced alloy. At 6 wt %-Si 3 N 4 , the material was about 4.4% and mass loss was observed in 9 wt% particulates with an 7.6% loss. This shows the positive effect of the inclusion of the Si 3 N4 helped in material saving for high temperature application by enhancing the reduction of mass loss with an optimal Si 3 N 4 amount of 3%.  The corrosion behaviour of materials has been studied using Electrochemical workstation. Figure 13 shows the potentiodynamic polarization graph for the Al 2219 allow with and without Si 3 N 4 reinforcement. From the results, the corrosion rate and the inhibition e ciency were calculated and is shown in Table 2. the results clearly shows that the corrosion rate decreases as with the addition of Si 3 N 4 which shows its positive effect on the material in preventing it from getting corroded. The inert properties of the nano ceramic Si 3 N 4 that makes it resistant to corrosion was seen to in uence the composite to have a low corrosion rate, its positive effect on the corrosion inhibition e ciency increases as the Si 3 N 4 percentage increases from 3% to 9%.

Conclusion
The Tribological, thermal, morphological and mechanical characteristics of AA2219 with four wt% of Si 3 N 4 composite was made by stir casting method. The study revealed the following results: to other the weight percentage. The intensity of facts initial will increase from 0% to 6% and then suddenly to 9%. The results of the tests like hardness and tensile increased with increasing the wt% of Si 3 N 4 in AA2219 composites [10] The XRD analysis of Al 2219 alloy / Si 3 N 4 composites reexhibits the aluminium, Silicon Nitride (Si 3 N 4 ) and intermetallic (Al-Cu) The tribological characteristicsmass wear, friction force and coe cient of friction, of the AA2219-Si 3 N 4 composites increases with the 9% of Si 3 N 4 The load factor and sliding speed is the controlling or dominated factor for wear tests, with increase in loads and speeds of sliding over the sample leads to signi cant increase in overall wear rate of the material. The AA2219-with-3, 6, and 9 wt. % of Si 3 N 4 composites has shown the lower rate wear compared to the original AA2219 alloy matrix. Work concluded that the 9% of Si 3 N 4 reinforcement is better for the wear resistances at minimum load applications of Aluminium alloy 2219 matrix materials. Work concluded that the minimum 6% of Si 3 N 4 reinforcement is better for the wear resistances at maximum load applications of Aluminium alloy 2219 matrix materials.
The wear rate is dominated by load factor and sliding speed. The increase in loads and sliding speeds leads to a signi cant increase in the wear rate. The AA2219-3, 6, and 9 wt. % of Si 3 N 4 composites have shown a lower rate of wear as compared to that observed in the as-cast AA2219 alloy matrix. For better wear resistance at the minimum load of application in Aluminium alloy 2219 matrix materials, the maximum amount of 9% of Si 3 N 4 reinforcement is to be suggested. For better wear resistance at the Maximum load of application in Aluminium alloy 2219 matrix materials, the minimum amount of 6% of Si 3 N 4 reinforcement is to be suggested.
The coe cient of friction and wear rate the of Al/ Si 3 N 4 MMC was found to be lower than that of AA2219. The smaller and ner grain size, improved hardness, reduction in the porosity level and uniform distribution of Si 3 N 4 particles are the various reasons for this. When the wt.% of Si 3 N 4 content increase the wear rate is found to be decreased with an increase in sliding velocity [23] The worn area shows a rough wear process, which is mainly the product of hard particulate exposure. In the case of AA2219/ Si 3 N 4 Composites, the particulate inhibits delamination progression, while the wear resistance is supplemental.
The corrosion resistance of the matrix alloy was improved when Si 3 N 4 particles were added in a quantity of up to 9% by weight. The AA2219-Si 3 N 4 alloy matrix composite showed high corrosion resistance with corrosion rates of 367.00 mil/year for 6 wt% Si 3 N 4 and 60 mil/year 9 wt% Si 3 N 4 . Heat treatment of the composites and matrix alloy improved corrosion and wear resistance.

Declarations
Funding statement: NIL  Tensile test specimen before testing (a) and after testing (b) Page 14/22 Effect of tensile strength on wt. % of Si3N4