Evaluation of Mechanical and Microstructural Properties of α-Brass Alloy Produced from Scrap Copper and Zinc Metal through Sand Casting Process

Cu-Zn alloy (Brass) is widely used as an industrial material because of its excellent characteristics such as high corrosion resistance, non-magnetism and good forging ability. This paper evaluates the mechanical and microstructure properties of α-brass alloy gotten from scrap copper and zinc metal, and compares the properties with normal α-brass billets. Five different compositions of the α-brass alloy (Cu-5%Zn, Cu-10%Zn, Cu-15%Zn, Cu-20%Zn, Cu-30%Zn) were produced from scraps of copper wire and zinc batteries casing respectively by method of sand casting. The parts of the cast rods were machined to a specification of 60 mm × 100 mm × 300 mm on a lathe to obtain tensile test specimens. After homogenization annealing, the samples were heated in an electric furnace at 500 ̊C for 3 hours. The samples were etched with ferric chloride solution for 20 seconds and sent for metallographic examination. The result of the hardness test shows variation in hardness of the cast Cu-Zn alloys with increasing zinc content. The ductility and elongation of the α-brass decrease with increasing zinc content. The colouration of the α-brass changed from red to yellow as the zinc content increases. In conclusion, hard brass can be obtained from recycled Cu and Zn as compared to normal brass billets.


Introduction
Brass is a metal alloy made of copper and zinc [1], whose proportions can be varied to create a range of brasses with varying properties [2]. The formation of brass makes it a substitutional alloy i.e. atoms of the two constituents may re- place each other within the same crystal structure [1]. Brass has higher malleability compared to its counterpart bronze [1]. However, both may also include small proportions of a range of other elements including arsenic, phosphorus, aluminum, manganese and silicon [1]. Generally, it has low melting point of about 900˚C to 940˚C (1652˚F to 1724˚F) depending on its composition. Its flow characteristics make it a relatively easy material to cast. By varying the proportions of copper and zinc, the mechanical properties of the brass can be changed, producing hard and soft brasses. The density of brass is approximately 0.303 lb/inch 3 (8.4 grams/cm 3 ) [3]. Cu-Zn alloy is widely used as industrial materials because of their excellent characteristics such as balance of strength, ductility, high corrosion resistance, non-magnetism and good formability [4]. Due to the excellent mechanical properties and machinability, it finds good applications in plumbing fixtures and fittings, low pressure valves, gears, bearings, decorative hardware and architectural frames [5].
According to [1] [4], several factors like corrosion resistance of brass to harsh environment, use in musical instrument industries, germicidal and anti-microbial application have contributed to increasing demands for brass alloy. In particular, electrical and electronic components' market of high performance and multifunctional has increased, and the amount of brass alloys in these products has also enlarged [4]. On the other hand, a weight reduction of parts and product is strongly required for the energy efficiency improvement of transport equipment or miniaturization [4]. An effect of brass alloy part with a high specific gravity on the weight ratio of the total product is large [4]. It is possible to produce the small parts by using the high strength brass alloy. Thus, the weight of the product will be reduced significantly.
Today, almost 90% of all brass alloys are recycled [6] due to non-ferromagnetism. It can be separated from ferrous scrap by passing the scrap near a powerful magnet. Brass scrap is collected and transported to the foundry where it is melted and recast into billet. Billet is reheated and extruded into the desired form and size. The study is aimed at evaluating α-brass obtained from scraps Cu and Zn so as to achieve the objectives of determining the microstructure and mechanical properties of the brass as compared to normal α-brass billets.

General Survey on Brass Prospects
Ozgowiez et al. [7] examined the influence of the recrystallization annealing temperature on the microstructure and mechanical properties of brass Cu30%Zn subjected to cold deformation in the process of rolling at various degree of strain. The mechanical test shows that there was deterioration in the properties of the brass and an increase in the plastic properties as the recrystallization temperature was increasing within the range 400˚C -650˚C (Table 1).
values in the nugget zones (NZs) were lighter than those in the parent material (PM). Increasing the rotational rates did not exert a noticeable effect on the tensile and yield strength of the welds but increased the elongation. Solid solution of chromium on the Cu-40%Zn-0.5Cr brass alloy extruded at a temperature is about twice as that of the same brass alloy extruded at a higher temperature. The strength impact of Cr solid solution was much effective compared to Cr precipitation strengthening. The grain size of extruded materials increased with increasing extrusion temperature (Figures 1-3).

Experimental Procedure
The Cu and Zn metals were purchased as scraps from copper wire and zinc battery casing respectively. Five different compositions of the alloy were prepared to give Cu-5%Zn, Cu-10%Zn, Cu-15%Zn, Cu-20%Zn and Cu-30%Zn alloy respectively. The total mass for each weight percentage was weighed to 1.5 kg. The alloys were prepared by method of sand casting. The sequence of production process involved in the casting is as follows: pattern making, mould and core making, casting, demoulding, removal of runner/riser and cast cleaning ( Table   2). The furnace charge was calculated using Equation (1): where X = constituent (Cu or Zn); R x = required mass of the constituent in the melt; T m = total mass of melt.
Parts of the cast rods were machined on a lathe to obtain the tensile test specimens. The rods were machined down to test specifications of 60 mm × 100 mm × 300 mm as shown in the Figure 4. The cast samples were subjected to homogenization annealing in order to homogenize the composition. They were heated in an OMSZON electrical furnace which was set to a temperature of 500˚C. The samples were soaked at this temperature for 3hrs and then allowed to cool slowly in the furnace. The grinding of each test sample was carried out under running water to avoid over heating of the sample with grinding machine

Hardness Measurement
The as-received samples and cast alloys were subjected to the hardness test using brinell hardness test accessory of the Mensanto Hounsfield Tensometer. Before the Tensometer was used, the compression attachments were mounted on the machine. After the whole setup, the corresponding Brinell hardness number was then calculated using the formula shown in the Equation (2) ( ) ( ) where P = applied load; D = diameter of the indenter; d = diameter of the impression.

Tensile Measurement
Samples from as-received and cast brass alloys that had been machined into tensile test pieces were subjected to tensile tests with the aid of a Monsanto universal testing machine. The test was carried out to determine the response of samples under the application of increasing stresses. Some properties of the alloys that were studied are as follows; yield stress, percentage elongation, reduction in area and ultimate tensile stress.

Hardness Test
The result of the hardness test was presented in Table 3. Also Figure 5 shows the variation in hardness of the cast Cu-Zn alloys with increasing zinc content.  As observed in Figure 4, the hardness value of the alloys increases as the zinc content increases. In the hardness test, severe plastic flow has been concentrated in the localized region directly below the indentation, outside of which the material still behaves elastically. Directly below the indentation, the density of the particles increased locally, compared to the regions away from the depression.
Since plastic deformation in crystals is caused by the motion of dislocations, any obstacle to dislocation motion will hinder deformation and the crystal is thereby strengthened [9]. Therefore, the increase in the hardness values of the alloys with increase in zinc content is attributable to solute hardening caused by the zinc solute atoms.

Tensile Test
The result of the tensile test was presented in the decreased. Therefore, the alloy with 20 wt% Zinc has the highest ductility ( Figure 6).

Micrograph of the Samples
From Figures 7-12, micrographs of the various alloys reveal the presence of a single solid phase which consists of a solid solution of zinc in alpha copper. Alpha brasses containing up to 20% Zn are reddish in colour. Above 20%, the brass is yellow in colour [10]. This is expected because based on the Cu-Zn phase diagram, zinc has complete solid solubility in copper up to 35% [11].

Conclusions
Hardness of the cast brass samples made from recycled copper and zinc metals increased with increase in zinc content which shows that, the higher the recycled zinc used in casting brass alloys, the harder the brass obtained.
Brass alloys made from recycled copper and zinc were seen to possess low tensile strength and ductility with increase in brittleness as the zinc content increased. This is an indication that when more zinc is added during the casting of copper alloys, for the production of brass, the brass obtained will have less tensile strength, low ductility, and high degree of brittleness. Generally an increase in the hardness of the cast brass obtained brought about an equal decrease in the tensile strength and ductility of the metal. Thus, in order to obtain an optimum brass cast, the zinc added to the copper must be at an optimum value. Therefore, recycled copper and zinc can be applied in brass production for engineering applications.