Effect of Tin Addition on the Mechanical Properties and Microstructure of Aluminium Bronze Alloyed with 4% Nickel

: The current study investigates the impact of adding tin to aluminium bronze alloyed with 4% nickel on its microstructure and mechanical properties. Sand casting was chosen as the most cost-effective and efficient method of preparing the aluminium bronze alloy. Following their melting points, six distinct samples of aluminium bronze alloyed with 0% to 10% tin were added into the crucible furnace. Nickel with the highest melting point of 1453°C was added into the crucible furnace first, while tin with the lowest melting of 231.9°C was added last into the crucible furnace. The alloying components were mixed well by manually mixing the liquid for around five minutes. After sand casting, the specimens were machined, sectioned, and grounded then tests were carried out to measure their hardness, tensile strength, and impact resistance. The results of the tests indicate that the tensile strength first increases and subsequently declines as the tin addition increases. The hardness of the aluminium bronze alloy increases as the proportion of tin addition increases. The results of the investigations also demonstrate that as the hardness of the specimens increases, their impact resistance decreases and the tensile stress of each specimen increases with strain.


Introduction
Tins are micro-alloyed precipitates that are insoluble in the heat affected zone of the weld and decrease grain growth.Additionally, tins are frequently used for wear prevention and have a high-temperature resistance.The manufacturing technology of powder metallurgy (PM) enables the cost-effective fabrication of intricate and high-quality components.Unlike ordinary bronze, which is made of an alloy of copper and tin as main alloying metal, aluminium bronze has aluminium as the primary alloying metal added to copper.The golden hue of the aluminium bronze eventually fades.For industrial usage, a variety of aluminium bronzes with various compositions are now usable.Aluminium makes up between 4 to 14% of the aluminium 4 bronze alloy, with additional alloying elements like nickel, manganese, zinc, chromium, and tin, and copper making up the remaining weight.On rare occasions, silicon is added as one of the alloying elements to produce aluminium bronze alloy (Kear et al., 2007;Oluwadare et al.,2019).

Suggested Citation
Aluminium bronze is more valuable than other bronze components because of its many qualities, including strength, resistance to corrosion, wear and great resistance to wear (Wharton et al., 2005).In addition to a tiny amount of nickel, aluminium bronzes and other alloys of similar kind offer flexible mechanical characteristics after heat treatment.Nickelaluminium bronze falls under the category of aluminium bronzes or various alloys based on copper that have tiny amounts of nickel added to them.It contains alloying metals in the following proportions: 9 -12 wt.% aluminium, 6 wt.% nickel, and additional metals in the designated range.According to Chen et al. (2007), it is among the best technical materials for heavy-duty uses in the oil and gas industry because of its superior strength and resistance to corrosion and wear.
A wide range of alloys are commonly used across various industries, and the aluminium-bronze alloy is especially useful in many engineering structures.Aluminium is the main alloying element in copper-based alloys.also referred to as aluminium-bronze alloys and is often found in the base alloy's composition between 4% and 14% (Meigh, 2007).Aluminium bronze alloys may occasionally have additional alloying elements purposefully added, such as zinc, nickel, iron, manganese, tin, etc., depending on the desired application and property modification.Additional alloying elements change the microstructure and enhance the mechanical qualities, including strength, toughness, resistance to corrosion, and magnetic behaviour (Oluwadare et al., 2019).Iron, for instance, refines grain, while nickel makes it more corrosion-resistant.Aluminium bronze is more durable than other copper alloys and can be used to make extruder rods, plates, sheets, and forgings.Due to its exceptional corrosion resistance, it is recommended as an essential engineering material for severely stressed components in corrosive conditions (Pisarek, 2007).Aluminium bronze is easily produced into parts like pipes and pressure vessels and is accessible in both wrought and cast forms.
Low alloy and stainless-steel costs are extremely high in Nigeria, and the materials are inevitable.Due to their excellent properties, requests for these materials have increased sharply in Nigeria and other African countries.An inexpensive substitute that serves the same purpose is needed.A well-prepared aluminium-bronze alloy can attain strengths comparable to low alloy steel and stainless steel.Oluwadare et al. (2019) studied the impact of nickel added to the aluminium bronze alloy and reported that the hardness of the aluminium bronze alloy increased as the percentage composition of nickel to the aluminium bronze alloy increased.The results conform to the earlier research reported by Adeyemi et al. (2014) that the hardness and yield strength of aluminium bronze alloy increased as the percentage of magnesium addition to the composition increased while the ductility of the metal decreased.The combination of chemomechanical qualities that aluminium bronzes provide surpasses many other alloy series.Because of this, they are highly favoured, especially for demanding applications ( (Pisarek, 2007).According to Wharton et al. (2005), "The greatest qualities of aluminium bronzes are their exceptional strength and resistance to corrosion in a variety of harsh conditions"; they are most frequently used in circumstances where their corrosion resistance makes them a better option than other engineering materials.Another fascinating aspect of aluminium bronzes is their biostatic properties.Copper alone has a significant impact on the fundamental characteristics of copper alloys (Pisarek, 2007).
In circumstances where such co-ionization would be undesirable, the alloy's copper component-which keeps aquatic organisms, including algae, lichens, barnacles, and mussels from colonizing-may be preferred over stainless steel or other non-cupric alloys.Aluminium bronzes have many advantages, including easy casting, fabrication, and machining, strength, hardness, corrosion resistance in various aggressive environments, wear resistance, low magnetic permeability, and non-sparking properties.They can also be readily welded in either cast or wrought form (Copper Development Association, 2006).Investigations by Yaro and Aigbodion (2009) revealed that aluminium bronze that has been gently cooled has very low ductility and moderate strength and hardness.According to the investigations, the alloy structure's coarse and segregated primary tin and nickel phases caused this mechanical behaviour.
Despite the fantastic qualities of aluminium bronzes, it is shocking to see that little research has been done on them in Africa, particularly in Nigeria.Steels, in particular, are ferrous materials used primarily in structural applications.Research has revealed that aluminium bronzes are quickly replacing modern steel materials in a few particular applications, particularly in parts used in marine and subsea applications.Because aluminium bronzes do not rust in marine conditions and can withstand corrosion even in highly demanding environments, their use has skyrocketed in the United States and other nations.For standard side vents, tops, and hoods of oxygen and electric arc furnaces, aluminiumbronze alloy construction was shown to be a practical substitute for carbon steel construction.According to Pisarek (2007), aluminium alloys have up to five times the lifespan of carbon steel equivalents.Propellers made of Manganesenickel-aluminum-bronze (Aqualloy) were discovered to have greater effectiveness than those made of stainless steel.Propellers, pump impellers, casings, and turbine runners can benefit from the extended service lifetimes and improved operational efficiency of nickelaluminium bronzes because they are more resistant to cavitation erosion than stainless steels from the 400 and 300 series, Monel alloys, and cast steel.The strength of aluminium bronze wire is almost equal to that of premium steel wire, and its castings are almost as complex as those made with steely iron (Nwaeju et al., 2017).
While there exist other categories for aluminium bronzes, according to multiple authors and organizations, 90% of them do not rule out the duplex phase group of aluminium bronzes, which is the primary focus of this study.With 8% to 11% aluminium, the dual (duplex) phase is the most alloyed and has the highest tonnage of all the aluminium bronzes.Iron and nickel are typically added for strength and to prevent or delay the decomposition of β solid solution to the (α + γ 2 ) eutectoid, as γ 2 is undesirable and can cause brittleness.For slow-cooling brittleness, 3% iron and 3% nickel were found to be the most appropriate (Copper Development Association, 2006).The best strength and ductility may be obtained by working or heattreating these dual-phase aluminium bronzes.When 10% aluminium-bronze alloy cools to equilibrium, α-aluminium bronze separates from β-aluminium bronze phases below 930˚C (Nwaeju et al., 2017).
Aluminium bronzes are the only alloys that meet the criteria for marine components in a maritime environment, which include a high ratio of strength to weight, superior castability, and tolerance of local working for mending damage experienced during service.This therefore forms the foundation of our research: creating an aluminium bronze in the (α + β) (α + γ 2 ) phase in order to find a substitute for commonly used parts that break easily under normal operating conditions (Yaro & Aigbodion, 2009)).
The impact of silicon percentage on bronze alloys' mechanical and acoustical properties for use in musical instruments was investigated by Kaplan and Yildiz (2013).Cut from 250 x 55 x 15 mm of billet, as-cast Cu (2.5-7.5)wt% Si was produced for test specimens for tensile, hardness, impact, and damping.The damping capacity was measured using a supported beam model.Silicon bronze's (Cu-Si) mechanical and damping characteristics were investigated.As a comparison, a study on bronze alloys containing 20% Sn was carried out.The findings showed that Cu-xSi bronze alloys had better mechanical characteristics and a higher damping capacity than Cu-20 wt% Sn bronze alloys.Additionally, silicon bronze had more excellent ductility and impact strength than tin Cu-20 wt% Sn.Daroonparvar et al. (2011) investigated how cold working affected the mechanical characteristics and structure of high-strength silicon bronze 6 (C65500).In order to improve the strength of the created alloy (C65500) through grain refinement without changing its chemical composition, it was exposed to severe plastic deformation through hydrostatic extrusion at room temperature.With a total true strain of 4.1, cumulative hydrostatic extrusion was used.Through the use of transmission electron microscopy, the microstructure of cold worked samples was assessed.Grain size was described quantitatively.Tensile testing and microhardness measurements were used to ascertain the resulting mechanical qualities.The study's findings showed that the cumulative hydrostatic extrusion method resulted in significant grain size refinement and increased strength.After undergoing standard plastic procedures, yield strength and ultimate tensile strength were found to be 130% and 45% greater, respectively, compared to the commercial alloy.Sekunowo et al. (2013) studied how the inclusion of silicon and tin affected the Cu-Si-Zn alloy's microstructure and microhardness.The range of tin concentrations in this investigation was 0.5, 1.0, 2.0, and 3.0 weight percent.Using an induction furnace, pure components were melted in a graphite crucible to create the silicon brasses.Every alloy's chemical composition was ascertained using X-ray fluorescence spectroscopy (XRF).The as-cast alloy's microstructure was examined using optical and scanning electron microscopy (SEM).Energy dispersive X-ray spectroscopy (EDS) was used to identify the phases' corresponding chemical analyses, and the Vickers hardness test was used to gauge each phase's hardness.The study's results showed that the hardness of brass that was 60Cu-0.5Si-39.5Zn was 123.4 HV.Additionally, it was demonstrated that the hardness value of the studied alloy rose with an increase in silicon concentration.Furthermore, when tin was added in addition to silicon, the amount of beta (β) phase and the uniform dispersive gamma (γ) phase were higher than when silicon was added alone.We may deduce that the tin addition made lead-free Cu-Si-Zn brass harder and generally worked better for machining.
The impact of adding tin (Sn) and various other elements within the Cu-Zn alloy's microstructure was studied by Nigam and Jain (2013).Additionally, an assessment was conducted on the relationship between the grain refiner and alloy elements (like Sn, Al, Bi, Se, and Pb) additions.Sn, Al, and Pb were added to the melted Cu-Zn alloy in the first melt.Pb, Sn, and Al were the revised addition orders in the second melt.Using the scale created as part of the experiment, the grain size of these castings was assessed.Additionally displayed were the corresponding macro and microstructures.The Cu-36% Zn alloy featured a high grain size, measuring 2.5μm.This alloy's microstructure comprised α dendrites, with some β phases in the interdimeric spaces and grain boundaries.It was also noted that every additional element introduced to this alloy changes the structure in size and components.Tin and copper formed a solid solution since tin was soluble in copper.It did not, however, alter the alloy's grain size.Also, it was discovered that the Cu-36% Zn alloy retained a coarse as well as dendritic structure despite the 0.35% Sn addition, although the dendrites were lengthier and well-defined.
The influence of Al and Ti additions on leaded brass alloys (CuZn39Pb3) performance was investigated by Donattus et al. (2012).They utilised a micro-Vickers hardness tester, known for its high precision, and a compression testing equipment, renowned for its accuracy, to access the mechanical characteristics of the specimens, including their hardness and compression strength.
The specimens' microstructure was examined using a light optical microscope (LOM) and an optical emission spectrometer (OES).The study's results showed that the addition of Al and Ti changed the alloy's microstructure, raising the material's hardness and compression strength.At 0.54wt% Al addition, optimum compression strength of 103.92KN was reached at 0.31%wtAl addition, while the lowest grain size of 8.38μm and greatest hardness of 54.10HV were acquired.Adeyemi et al. (2014) investigated the effects of varying amounts of manganese and aluminium addition on the mechanical characteristics of brass.Separate additions of manganese and aluminium were made to pure red brass at concentrations ranging from 1 to 10 per cent weight.Using the Monsanto tensometer and Izod testing equipment, standard specimen preparation techniques were used to assess the mechanical attributes, including hardness, impact strength, and tensile strength.The findings showed that as the quantities of manganese and aluminium rose to 5%, the mechanical qualities of brass improved.All of the examined mechanical qualities decreased as the elemental concentration increased more.This current study investigates the effect of tin addition on the microstructure and mechanical characteristics of aluminium bronze alloy containing 4% nickel.The specific objectives of the study involve preparing cast samples and conducting tests to determine the strength, hardness, and impact resistance of each aluminium bronze alloyed with tin.By adding tin and 4% nickel to aluminium bronze, the study aims to create new aluminium bronze with increased strength and hardness while maintaining its superb ductility and electrical conductivity.This would undoubtedly increase the alloy's applications in marine and subsea, the building, automotive, and electrical industries and could significantly impact the field.

Materials and Equipment
For this study, the following materials and equipment were utilised:

Method
The approach used to conduct this study entails melting and casting procedures for alloy preparation.The Department of Mechanical Engineering at Obafemi Awolowo University of Ife, Osun State, Nigeria, provided the copper, aluminium, nickel and tin utilised to create aluminium bronze alloy.Tin was added in a proportion ranging from 0 to 10%.
Due to nature of the study, the mixture/ addition of tin to aluminium was done carefully and to achieve the aim and objectives, the following steps were carried out:

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Melting and casting of alloys

Melting and Casting of Alloys
Six specimens were created for the mechanical testing.Nickel (Ni), copper (Cu), aluminium (Al) and tin (Sn), were weighed using the digital weighing balance.The required weight for each specimen was prepared and added into a pit-type crucible furnace with a graphite crucible pot that had been preheated to 1500 o C for approximately ten minutes.Nickel was added first, followed by copper then aluminium, and tin was added last due to its lower melting temperature.The crucible furnace used for this study could melt the materials at low temperatures without evaporating.After stirring the mixture for around five minutes to ensure homogeneity, the molten metal was poured into mould cavities and left to solidify for approximately 30 minutes before being removed.The addition of all the elements for each specimen being 500 g is a significant finding.It shows that the composition of each specimen was consistent and carefully measured.Table 1 shows the percentage composition ratio for each specimen prepared in this study.

Specimen Preparation for Hardness and Tensile Tests
A lathe was used to machine the cast tinaluminium bronze rods in order to prepare them for the specimens' tensile and hardness tests.
The specimens underwent a turning operation to create the necessary sizes and shapes for tensile testing.As shown in Figure 1a, the shoulder diameter was machined to 6 mm, with the grasping length also 15 mm.The tensile specimens' diameter was decreased to 4 mm, and the gauge length was shortened to 30 mm.

Mechanical Testing
Tests were conducted at the Centre for Energy Research and Development (CERD), Obafemi Awolowo University in Ile-Ife, Nigeria.An Instron universal tensile testing machine (model 3369) was used to measure the tensile strength property of the aluminium bronze alloyed with tin, and a Brinell hardness testing machine was used to measure its hardness.Each prepared specimen was subjected to a constant extension rate tensile of 5 mm/min on the machine during the tensile test.As the testing continued, the machine plotted tensile force against the displacement.Additionally, the machine measured characteristics such as yield point, tension, strain, and elongation (%).In this investigation, an average of three observations was taken into account.The hardness test was conducted on the polished, flat surface hardness test specimens, each having a 10 mm diameter and 15 mm high.For every test, a pyramid indenter was carefully placed on the specimen surface, and a force of about 588 N was exerted and maintained for about 12 seconds.After that, the specimen's indentation was measured, converted to a hardness value, and shown on the tester monitor.Three indentations were made for every specimen, and the mean value was calculated.

Hardness Test
The Tensile tests were conducted at the Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, Nigeria.All specimens underwent tensile strength testing by the ASTME8 standard.Three identical test specimens for each section thickness per sample were assessed at room temperature with a strain/loading rate of 5 mm/min using a computerized Instron Testing Machine (model 3369).The results obtained from the tensile tests are shown in Table 2. 11 Adding tin to aluminium bronze alloy enhances the alloy's maximum tensile stress.As the proportion of tin content in the alloy increases, the value of maximum tensile stress increases gradually and then significantly, as shown in Table 2.The maximum tensile stresses for the alloy at 0%, 2%, 4%, 6%, 8%, and 10% tin are 202.29 MPa,202.64 MPa,205.24 MPa,285.16 MPa,381.71 MPa,and 399.40 MPa, respectively.
The results conform to the previous investigations of Oluwadare et al. (2019) and Adeyemi et al. (2014) on aluminium bronze alloyed with different alloying elements Nickel and Magnesium, respectively.Moreover, a high tin content in aluminium bronze alloy results in excessive precipitation hardening, which weakens the material and makes it more brittle, as shown in Figures 2 (a -f).Table 3 shows the results obtained from the Brinell Hardness Testing Machine.The machine comprises a hard, spherical indenter to press the surface of the metal.Standard loads are maintained constant for a predefined period (between 10 and 30 seconds) throughout testing, ranging from 500 to 3000 kg in 500 kg increments.Higher applied loads are necessary for harder materials.The diameter of the resultant depression and the applied force impact the Brinell hardness number, or HB.An engraved scale on the eyepiece of a special lowpower microscope is used to measure this diameter.Afterwards, a chart is used to translate the measured diameter to the relevant HB number.
There are semiautomatic methods for measuring Brinell's hardness.These utilise optical scanning devices, which place the camera above the depression using a flexible probe placed on a digital camera.A computer receives data from the camera to evaluate the indentation, calculate its size, and determine its Brinell hardness number.Surface finish specifications for this method are typically stricter than those for manual measures.The parameters for minimum indentation spacing, maximum specimen thickness, and indentation location (with respect to specimen edges) are the same as for Rockwell testing.Furthermore, a precisely defined indentation is needed, which calls for a flat, smooth surface to be used for the indentation.
The sample was prepared and cut to get a specific length.After that, the sample being cut was filed using a hand file to harden the surface of the sample; this was said to have been done correctly, provided one could see the image of the teeth on the surface of the filed sample.It was later ground by using the grinding machine, which polishing the surface came after that.The sample was then secured in the tensiometer and compressed with a 500 kg force for approximately 15 seconds.The indentation diameter was then measured using an eyepiece, and the Brinnel or hardness number was determined using the conversion table.The pressure per unit surface area of the identification in kilograms per square meter, or the Brinell Hardness Number (BHN), is calculated as follows: where; W is the load on the indenter, D is the steel ball's diameter, mm d represents the indentation's average measured diameter, mm The addition of tin to aluminium bronze alloy increases as the percentage of tin addition increases, as shown in Table 3. Figure 3 shows the relationship between hardness and the percentage of tin addition to aluminium bronze alloy.As the tin addition increases from 0%, 2%, 4%, 6%, 8% and 10% , the value of hardness increases as 58.73BHN, 59.57BHN, 61.86BHN, 72.21BHN, 80.59BHN and 84.67BHN, respectively.Also, Table 3 shows that the maximum tensile stress increases as the hardness of the metal increases.The results conform to the previous findings of Oluwadare et al. (2019) and Adeyemi et al. (2014).Results on Microstructure (Metallography) studie metals and alloys crystalline structures and how these structures relate to the metals' physical characteristics.Through microscopic examination of properly prepared specimens, it is possible to ascertain the dimensions, composition, and orientation of the metal crystals.Through these analyses, metallurgists can often determine the identity of a metal or alloy and assess how well heat treatments for annealing or hardening are working.In order to bring out the grain structure, metal specimens for metallographic analysis are often highly polished before being etched with etchants.This process targets one of an alloy's constituents or the boundaries between the grains.Metals are inspected using a low-power microscope with high magnification.Since bulk metals cannot transmit an electron beam, a thin, electron-transparent cast of the etched surface can be created.An incredibly thin specimen, on the other hand, can also be created; the microstructure observed is a projection of the microstructure contained within the thin specimen.
The etchant used for the specimen to derive the results in Fig. 4 (a-f) is 2% Ferric Chloride and the magnification used is X420.Increasing Tin contents gives a lighter coloured microstructure of α + β multi-phase.This is evident in Fig. 4 (d, e and f) simply because of the increase in the Tin content.
Fig . 4 (d) shows the optical microstructure with the addition of 6% Tin to the aluminium bronze alloy.The material becomes harder due to the larger tin atoms limiting the mobility of the copper atoms.An impact vibrates the atom.Even though tin is not very soluble in copper at a normal temperature, it is a solid solution strengthener in copper.The above microstructure has the highest tin percentage and gives a better lighter coloured microstructures of alpha plus beta multi-phase.
It also has a huge amount of precipitates from alloying in the inter-granular zones.The alpha -beta phases are more distinct and pronounced.

Results on Impact Test
Before fracture mechanics became a recognized scientific field, impact testing methods were developed to determine the properties of fracture in various materials.It was shown that laboratory tensile test results could not predict fracture behaviour; for instance, under some situations, ordinarily ductile metals shatter abruptly and with very little plastic deformation.Impact test conditions were chosen to represent those most severe relative to the potential for fracture namely: 1) Deformation at a comparatively low temperature 2) A high rate of strain, or deformation 3) A triaxial stress condition, which a notch might potentially introduce.Impact has a crucial role in determining how long a structure lasts.A given arm raised to a certain height releases consistent potential energy.The sample breaks when the arm strikes it, and the impact strength is measured by the energy the sample absorbs.In contrast to the Charpy impact test, which uses a three-point bending arrangement, the Izod impact test uses a cantilever beam configuration for holding the sample.The notch sensitivity can also be assessed with this test.The results of the impact tests on the prepared specimens are shown in Table 4.As the percentage of Tin addition increases, the impact resistance of the specimens decreases as shown in Figure 5.

Conclusion
The effect of tin addition on aluminium bronze alloyed with 4% nickel has been experimentally investigated.The results of the investigations show changes in the mechanical properties and the microstructure of the metal.As the percentage of Tin addition to aluminium bronze alloy increases, the following conclusions are reached based on the test results:

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The results have shown that the increase in tin addition to aluminium bronze alloy increases the tensile strength of the metal.

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The hardness of the metal increases as the Tin addition to aluminium bronze alloy increases.

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The impact strength of the aluminium bronze alloys reduces as the percentage composition of tin increases.

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Because of the increase in the value of the hardness property due to the Tin addition, the results of this research have revealed that aluminium bronze alloyed with Tin will be beneficial in high-stress situations, particularly for creating the cutting tool's tips.Also, this will undoubtedly increase the alloy's applications in marine and subsea, the building, automotive, and electrical industries and could significantly impact the field.

Figure 1 .Figure
Figure 1.Machined samples of the (a) tensile test specimen and (b) Hardness test specimen

Figure
Figure 2(a).0% Tin Addition to Specimen A

Figure 3 .
Figure 3. Hardness Against Percentage of Tin Addition to Aluminium Alloy

Fig. 4
Fig. 4 (e)  shows the optical microstructure by adding 8% of Tin to the aluminium bronze alloy.The alpha phase is more pronounced.Cored dendrites with an increasing tin composition gradient as they grow make up the microstructure seen above.Based on the Cu-Sn binary alloy phase diagram, at solution temperatures between 630 o C and 720 o C, the solid solubility of the Sn element in the α-Cu matrix steadily declines as temperature rises.In contrast, the theoretical solid solubility value, the alpha phases are predominant in Fig.4(e) compare toFig.4 (d).

Fig. 4
Fig. 4 (f) shows the optical microstructure by adding 10% of Tin to aluminium bronze alloy.The above microstructure has the highest tin percentage and gives a better lighter coloured microstructures of alpha plus beta multi-phase.