MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 63ISSN 2230-7680 MIT Publications

Brass is one of the most important domestic, industrial and ornamental alloy of Cu and Zn. Different compositions of brass ranging from Cuwt% 60 to 80 are used wide over. In present study, brass in four compositions has been prepared by sand casting and optical micrography hasbeen done to compare the effect of composition on microstructure. The superheat temperature has also been varied in two steps viz. 980 oCand 1100oC and the effect on microstructure has been reported.Keywords-Brass, Microscopy, Dross, Grains, Casting.

Micrography of Different Compositions of BrassDeveloped at 980oC and 1100oC

I. INTRODUCTIONBrass alloy is used over a wide spectrum of applications inmanufacturing of machine components varying from electrical/mechanical to chemical process equipment. Such componentsinclude nuts, bolts, valves, bath fittings, tubes, pipes, bushes,connectors and many kinds of fittings, which are produced bycasting, automatic machining processes or hot stamping ofextruded and drawn brass rods [1-3]. Brass has a characteristicappearance which resembles gold, a symbol of elegance,prosperity, purity and beauty. None other metal oy alloy thanbrass has similar appearance with much lower cost than goldand hence the importance of brass as a domestic and industrialmaterial is unmatched. To some extent, titanium alloys havesimilar finish as gold but their cost is nearly as much as or evenhigher than gold. Brass products can be readily electroplated byChrome, Nickel, Silver, Gold, Platinum etc. It can be lacqueredfor corrosion prevention and many other decorative treatmentsmay be applied over them such as oxide coloring, making themmost attractive alloy for decorative domestic applications.

Metallography is the study of metals by optical and electronmicroscopes. Structures which are coarse enough to bediscernible by the naked eye or under low magnifications aretermed macrostructures. Useful information can often be gainedby examination with the naked eye of the surface of metal objectsor polished and etched sections. Those which require highmagnification to be visible are termed microstructures.Microscopes are required for the examination of the

microstructure of the metals. Optical microscopes are used forresolutions down to roughly the wavelength of light (about halfa micron) and electron microscope are used for detail belowthis level, down to atomic resolution. Microscopy may giveinformation concerning a materials composition, previoustreatments and properties. Particular features of interest are; grainsize, phases present, chemical homogeneity, distribution ofphases, elongated structures formed by plastic deformation etc.

A. Commercial Utility of BrassBrass is the generic term for a range of copper-zinc alloys withdiffering combinations of properties, including strength,machinability, ductility, wear-resistance, hardness, color,antimicrobial properties, electrical and thermal conductivity and,corrosion resistance. Brasses set the standard by which themachinability of other materials is judged and are also availablein a very wide variety of product forms and sizes to allowminimum machining to finished dimensions. Brass does notbecome brittle at low temperatures like mild steel. Brass alsohas excellent thermal conductivity, making it a first choice forheat exchangers (radiators). Its electrical conductivity rangesfrom 23 to 44% that of pure copper. Silver colored copper-nickel-zinc alloys containing 10-20% nickel can be regarded as specialbrasses. Mostly they show similar corrosion characteristics tothe brasses, but the higher nickel versions have superior resistanceto tarnish and stress corrosion cracking. They are available inall forms and are used for tableware (silver-plated),

Pooja VermaPG Student, Deptt.of

Mechanical Engg., MITMoradabadU.P., INDIA

Nitin AgarwalAssociate Professor, Deptt.

of Mechanical Engg.MIT Moradabad

U.P., INDIA

Abhishek SaxenaAssistant Professor, Deptt.

of Mechanical Engg.MIT Moradabad

U.P., INDIA

ABSTRACT

Vineet TirthProfessor, Deptt. ofMechanical Engg.&

Director, MIT MoradabadU.P., INDIA

MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 64ISSN 2230-7680 MIT Publications

telecommunication components, food manufacturing equipment,jewelry, model making, tool brush anchor wire and pins, musicalinstruments, e.g. silver bands, flutes, test probes and contactsprings.

B. Colors of Brass

Brasses have a range of attractive colors viz. red, yellow, gold,brown, bronze, silver etc. Brass with 1% manganese will weatherto a chocolate brown color. Nickel silvers will polish to a brilliantsilver color. Brasses are easy to shape and, with all these colorsavailable, it is not surprising that architects and designers haveused brasses to enhance the appearance of new and refurbishedbuildings, both inside and out.

C. Brass and HygieneCopper and brass are playing a leading role in the fight againsthospital-acquired infections. It has been shown that thesepathogens, which may spread by touch, will die in few hours oncopper/brass surfaces. This does not happen on stainless steel orplastic.

D. Recycling BrassThe brass industry throughout the world is well organized andequipped to recycle products at the end of their long service lifeand process scrap. Making brass from new (virgin) copper andzinc would be uneconomical and wasteful of raw materials sonew brass products are made from recycled scrap, illustratingthe sustainable nature of this material. In UK, brassmanufacturers use almost 100% brass scrap.

II. LITERATURE REVIEWSignificant research has been carried out on microscopic studyof different compositions of brass. Oca et al. [4] studied thesurface degradation of nickel-plated brass fittings designed forornamental plumbing purposes using optical and scanningelectron microscopy together with energy dispersive and X-raydiffraction analysis. Mapelli et al. [5] performed the failureanalysis on different brass electro-valves body affected byunexpected phenomena of cracking. Through the application ofoptical and scanning electron microscopy, micro hardness Vickerstest and X-ray diffraction, the causes of damage were identified.The study showed the dependence between roughness andresidual stresses associated to the tool wear. A solution to avoidthe failure is to use the combination of a tool with controlledwear and stress relieving heat treatment.Ameen et al. [6] investigated the effect of short and long cracksfor brass alloys specimens exposed to bending cyclic load. Thistest has been applied on a group of standard specimens until itsfracture; data taken could be drawn as a curve between stressand number of cycles (S-N) which gives the fatigue limit. Results

obtained theoretically and experimentally indicated decrease inthe applied load cause increase in the age and applying highloads in the beginning and at the end giving smaller specimenage and the quick growth of short cracks followed by quickgrowth of long cracks. The values taken from the theoreticalequations have been found to be greater than experimental values.He et al. [7] performed transmission electron microscopy andtensile tests to study alpha-brass nano-ligament deformation,phase transformation and fracture. Phase transformation and itseffect on alloy nano-crystal fracture were also studied. Neishi etal., [8] studied superplastic deformation in brass 60%Cu-40%Zn brass at relatively low temperature.In the light of commercial and domestic utility of brass, in presentstudy, an attempt has been made to process most widely usedcompositions of brass viz. 80wt% Cu-20wt% Zn, 70wt% Cu-30wt% Zn, 75wt% Cu-25wt% Zn, 60wt% Cu-40wt% Zn.

III. EXPERIMENTAL SET-UP

Brass was prepared with nominal compositions 80wt% Cu-20wt% Zn-designated as 8020, 70wt% Cu-30wt% Zn-designatedas 7030, 75wt% Cu-25wt% Zn-designated as 7525 and 60wt%Cu-40wt% Zn-designated as 6040.Micro controlled basedelectric resistance furnace with Kanthal A-1 element and K-typeAlumal-Chromal Thermocouples has been employed for casting,represented in Fig.1.

Fig. 1. Micro controlled based electric resistance furnace withKanthal A-1 element and K-type Alumal-Chromal Thermocouples

Hardness testing has been done on computerized BrinellHardness Testing Machine, Model-B-1000PC 250, Make FIE,Kolhapur, India, load capacity (500-3000 kgf). Hardness testinghas been done as per ASTM E10 standard by applying 31.625kg load with steel ball for 15 s. The Brinell hardness testingmachine is shown in Fig. 2.

MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 65ISSN 2230-7680 MIT Publications

Fig. 2. Brinell hardness testing machine

Optical microscopy has been used to examine microstructuresof polished specimens of different compositions of brass in etchedand un-etched conditions. Etching has been done with HnO3 (80ml) and distilled water (20 ml) applied by immersion for 40 s.Microstructures have been examined at 100x to see the effect ofsuperheat temperature and holding time. Polished specimens havebeen prepared by standard metallographic procedure.

Fig. 3. Dewintertrinocular inverted metallurgical microscope

Microstructures have been examined using Dewintertrinocular

inverted metallurgical microscope model; DMI victory. DewinterMaterial plus software 4.2 has been used for metallurgicalanalysis. Microscope is represented in Fig. 3.

IV. RESULT AND DISCUSSIONThe micrographs are in unetched and etched conditions and arecompared in the light of known physical phenomenon andresearch knowhow. Results are reported and discussion is madesimultaneously comparing the micrographs.

Fig. 4. Unetched micrograph of 60wt% Cu, 40wt% Zn Brassprocessed at 980oC with 15m holding time at 100x.

Fig. 5. Unetched micrograph of 60wt% Cu, 40wt% Zn Brassprocessed at 1100 oC 15 m holding time at 100x.

Fig. 4 and 5 represents the optical micrographs of brass with60 w% Cu and 40 wt% Zn, processed at 980oC and 1100oCrespectively with 15 m holding time. This composition has beendesignated as 6040. Holding time is required because aftermelting, some time for diffusion of atoms and homogenizationof the composition is to be given to the alloy. On comparing themicrographs in Fig. 4 and 5, we may observe that the surface ismore smooth at 980oC but at 1100oC the surface becomes roughand some scales are appearing on the surface. Such scales are a

MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 66ISSN 2230-7680 MIT Publications

common defect in high zinc yellow brass and are called alligatorskin. Dark spots on the surface of micrographs are due to porosityin which the debris has been trapped at the time of polishing.Figs. 6 and 7 show etched micrograph of 6040 brass at 980 oCand 1100oC. It may be observed that at higher processingtemperature, the grain size has increased. Dendrites are observedin both the micrographs forming cells in Fig. 7 whereas inFig. 6 we see fine dendrites with secondary arms. It is henceseen that due to increase in superheat temperature, bigger grainshave formed and instead of development of secondary arms,dendrites have grown thicker and forming closed cells.

Fig. 6. Etched micrograph of 60wt% Cu, 40wt% Zn Brass processedat 980oC 15m holding time at 100x.

Fig. 7. Etched micrograph of 60wt% Cu, 40wt% Zn Brass processedat 1100 oC 15m holding time at 100x.

Fig.8 and 9 represent 7030 brass superheated upto 980oC and1100oC. Alligator skin defect is seen over the micrographprocessed at 1100oC and some inclusions or dross particles areseen in micrograph processed at 1100oC.

Fig. 8. Unetched micrograph of 70wt% Cu, 30wt% Zn Brassprocessed at 980oC 15m holding time at 100x.

Fig. 9. Unetched micrograph of 70wt% Cu, 30wt% Zn Brassprocessed at 1100 oC 15m holding time at 100x.

Fig. 10. Etched micrograph of 70wt% Cu, 30wt% Zn Brass pro-cessed at 980oC 15m holding time at 100x.

MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 67ISSN 2230-7680 MIT Publications

Fig. 11. Etched micrograph of 70wt% Cu, 30wt% Zn Brass pro-cessed at 1100 oC 15m holding time at 100x.

Etched micrograph of 7030 brass processed at 980oC and1100oC in Fig. 10 and 11show up dendrite cells but it may beobserved that the cell sizes are bigger in micrograph processedat higher temperature. This may be due to more nucleation sitesin brass processed at 980 oC as compared to the one at highertemperature. Different phases are observed in both themicrographs probably due to different phases or differentialetching as a result of variation in composition across the surface.

Fig. 12. Unetched micrograph of 75wt% Cu, 25wt% Zn Brassprocessed at 980oC 15m holding time at 100x.

Figs. 12 and 13 represent 7525 brass at 100x processed at lowand high temperatures respectively. We may see that as thecomposition of Zn has reduced, microstructure is appearingcleaner. At high temperature also, the alligator skin defect is notobserved.

Fig. 13. Unetched micrograph of 75wt% Cu, 25wt% Zn Brassprocessed at 1100 oC 15m holding time at 100x.

Fig. 14. Etched micrograph of 75wt% Cu, 25wt% Zn Brass pro-cessed at 980oC 15m holding time at 100x.

Fig. 15. Etched micrograph of 75wt% Cu, 25wt% Zn Brass pro-cessed at 1100 oC 15m holding time at 100x.

MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 68ISSN 2230-7680 MIT Publications

In etched micrographsof 7525 brass processed at low and hightemperatures, shown in Figs. 14 and 15, one may see very finedendrite structure in low temperature brass. Bigger grains andbroader cells are seen in high temperature brass but if thismicrograph is compared with 7030 and 6040, the dendrite cellsare not clear and closed and their walls are also not that thick.The micrographs of 8020 brass shown in Figs.16 and 17 revealclear surface with minimal dross formation. Some microporesare seen at low processing temperature in Fig.16 whereas numberof these micropores appear to be increasing at high processingtemperature as seen in Fig. 17.Here in etched micrographs of8020 brass processed at low and high temperatures in Figs. 18and 19, we see that dendtite cells are fine and small in size at lowprocessing temperature.

Fig. 16. Unetched micrograph of 80wt% Cu, 20wt% Zn Brassprocessed at 980oC 15m holding time at 100x.

Fig. 17. Unetched micrograph of 80wt% Cu, 20wt% Zn Brassprocessed at 1100 oC 15m holding time at 100x.

Minimal dross is abserved along the edges of the cells. At highprocessing temperatures, we can see that cells are not formedbut bigger grains are being observed. Dross is in the form of fineparticles scattered around the surface of alloy.

Fig. 18. Etched micrograph of 80wt% Cu, 20wt% Zn Brass pro-cessed at 980oC 15m holding time at 100x.

Fig. 19. Etched micrograph of 80wt% Cu, 20wt% Zn Brass pro-cessed at 1100 oC 15m holding time at 100x.

V. CONCLUSIONSFollowing broad conclusions may be drawn from this study:

1. As the wt% of Zn has increased in the alloy, drossformation has increased due to more oxidation.

2. Alligator skin defect is observed in high Zn wt% brass(6040 and 7030). This defect is not visible in low Zn andhigh Cu brass (8020 and 7525).

3. Within same Zn wt% brass (6040 and 7030) the alligatorskin defect is observed in brass processed at highsuperheat temperature (1100 oC).

4. With the increase in superheat temperature;a. The dross formation has increased due to increase in

oxidation.b. The dendrite cells have become thicker due to more

time available for their growth.

MIT International Journal of Mechanical Engineering, Vol. 4, No. 1, January 2014, pp. 6369 69ISSN 2230-7680 MIT Publications

c. The dendrite cell size has become bigger due to moretime available for solidification and hence slownucleation.

d. The grain sizes have become bigger due to morecooling time available and hence more time availablefor grain growth until the grain boundary of adjacentgrain intersects and both boundaries fuse together toform grains.

e. The defect of alligator skin is observed in brass athigh processing temperature.

5. For economic point of view, it may be concluded fromcomparative study of micrographs that low superheatingtemperature (980 oC) should be used to minimize drossformation and getting high casting yield. The holding timeshall also be kept to minimum.

ACKNOWLEDGEMENTSThe authors gratefully acknowledge the financial support givenby AICTE under Research Promotion Scheme and the facilitiesand resources provided by Moradabad Institute of Technology,Moradabad-India for carrying out this work.

REFERENCES

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[3] G.A. Pantazopoulos, A.I. Toulfatzis Fracture Modes andMechanical Characteristics of Machinable Brass Rods.Metallography, Microstructure, and Analysis, 1 (2), 2012,pp. 106114.

[4] N.F. Garza-Montes-de-Oca, N.A. Garca-Gmez, I. Alvarez-Elcoro, R. Colsa. Surface Degradation of Nickel-plated BrassFittings.Engineering Failure Analysis, Volume 36, 2014, pp.314321.

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[7] Y.I. He, Y.J. Yan, L.J. Qiao, Alex A. Volinskya. In situTransmission Electron Microscopy Study of Alpha-brassNanoligament Formation, Microstructure Evolution andFracture Scripta Materialia Volume 65, Issue 5, 2011, pp. 444447.

[8] K, Neishi, T, Uchida, A. Yamauchi, K, Nakamura, Z., Horita,T.G. Langdon, Low-temperature superplasticity in a Cu-Zn-Snalloy processed by severe plastic deformation, Materials Scienceand Engineering, A307, 2001, pp. 23-28.