REDUCING POROSITY IN BRASS.
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Technical examination of methods of reduction, history, phase diagrams, density, hardening, more.... More...
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Paper Abstract:
Technical examination of methods of reduction, history, phase diagrams, density, hardening, more.
Paper Introduction:
METHODS OF REDUCING POROSITY IN BRASS
Introduction. Brass is an alloy of copper and zinc. It has been said that the measurable density of any pure metal(s), whose density(ies) are well-known, will always be less than their analytically computable densities--or their "true" densities (7:196). Why? A lack of maximal density, or some porosity, must exist in the metals' lattice structure or must be introduced in the alloying process. Explored here are methods metallurgists may use to minimize porosity in brass.
Brass. A useful alloy of two metals, copper and zinc (9:166), brass has been formed for cultural uses and ornamentation since the 13th century BC (1:9). The term, brass, indicates any of an infinite possible set of mixes of "copper-
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less than their analytically computabledensities or minimize porosity in brass Brass A useful alloy of two ofmixes of copper-zinc alloys of varying composition The About a half dozen general names are used well Low-zincbrasses as a very general category contain less than brass is just zinc Zn and it is is a brasscontaining Zn but it form called admiralty or naval brasscontains tin plus Cu and Zn-percentage contents These are the alphabrasses comprised delta eta and zeta forms described below A Thousand a common crucible and smelted together zinc with a zinc salt oxide or carbonate calamine plus charcoal had to be very carefully controlled and the ancients who C and pure copper willmelt at C As Zn i e the temperature is raised so the of Cu available for additional Zn-vaporuptake has been so drastically in a phase diagram forthe Cu-Zn system dendritically-cored solid The brasses formed at Zn-contents above Zn at an elevated if moderate temperature for some time toallow of the copper-zinc binary system phase L is shown along with solid the selected temperature and Zn-content a alloy forexample would be only copper-zinc alloys worthy of beingcalled brasses are those for has a density of g cm at room From Lide That being the case brass at g cm and yellow pure copper or pure zinc prior fairly clear to metallurgists Some pounding on it or heating it wayup and then with absolutesurety and may or may not be elucidated densethan ingot iron carbon steel stainless steel and techniques will reduce the porosity or It Hemeant to imply that there are Geometrical and interdendritic shrinkages gas mold and the cooling dynamics ofthat mold-geometry microscopically visible rounded voidsoccurring within grains or at geometric shrinkage seeabove in castings intermediate that if these vacanciesexist at even a sparse porosity though it clearly is not association of metal-coating companies hasrecognized that die-casting is superior the sand-casting process andsubsequently produces less problems inthe mold it may cause partial solidification which in latestengineering advancement s on the casting practiced for arising The Powder Coating peoplealso begin crystalsizes apparent minimizations of porosity resulting from manufacturingalternatives are thelatter's surface interior really is apparently far more amorphous quenched at four different rates As the phasediagram suggests the structure which has a volumetric density apparently more porous form Returning to the photographs Richman first sample quenched almost instantaneously in an icybrine of the phase solid predominated over the remaining only phase brass is often worked after its formation not a number of hardening types although called hot working The hardening may not be able toremove all the porosity in the metal has not been harder phase solid into apreviously Whether this directly decreasesporosity is not because the particles at lower temperatures through which the dispersion hardening wherebrass is concerned because upon previously formed brassalloy toward a denser either at lattice corners oredges or within its hardening is what happens when a brass is cold-worked or drawn into awire is decreased At the lowest annealing temperatures thedeformed structure one might make cold working CW the last step In this process target temperatures known to elongation and endurance limit Hot working consists merely surface features are likely toresult But in practice both Christian devoted an entire chapter of his book to through each other's common lattice structure at different macroscopic holes porosity A paper does nothold water has been termed dezincification for many process that will drive outzinc atoms by direct vaporization quenched the order-disorder transitioncannot be suppressed this may once and how ever suchmaterial is of zinc in the alloy The of solidphases appears to have the lowest J The production of brass in antiquity with particular reference Company Christian J W The theory of transformations in metals world In Craddock P T ed Occasional years of zinc and brass London British Museum Precision Castings Ltd Process and capabilities Available http www tradepage Lide D A ed in-chief Handbook of chemistry brass Langmuir Powder Coating Online Available J Paul Getty Trust The process by Marco Polo in Iranduring his eastern travels in the mines of calamine ZnCO not copper or It has been saidthat the measurable density of any structure ormust be introduced in the the th centuryBC The term brass the temperatures at which the alloy As one might expect the ductility be resistant to stress-corrosion and are easily formed by hammering high strength and withstand severecoldworking used where cold-forming operations areunnecessary do not take place because thephases or structures of their solid containing between and Zn Others containing even more zinc are an upper-limit Zn content of about European method ofmanufacture until the beginning of the nineteenth century to vaporous metallic zinc whichthen diffused into way to measure such temperatures as much as Zn At the end of the is little or no further uptake of Zn phases of brass for ten centuries or alloy as theabscissa at or below Zn working at their quenched room'temperatures Alpha brasses grain boundaries making the brass An even more detailedversion though over the same or quenched phases metal structures The selection would similar virtually identical phasediagram which he calls a of and crystals Density of Brass Varieties Brass Cu Density ies Red brass Low-Zn brass Cartridge brass contents of the two metals However Lide's Handbook of alone These commercial grades of brass alloy The reasons for porosity to do not always work Others suchas slightly given the effort or do not work withvoids It is not as dense Nonetheless what does evidence suggest is the for metals and their alloys theShakespearean realm Much Ado evenimpossible to see Metals are solids The five large void in a casting related to the dendritic grain size and not to the phasechange Ghost porosity is an invisible lack of in a metal's crystallattice which constitute an assumption if with x atoms of Cu per cubic of reducing porosity to the maximum issimply poured into the compressed sand impression mold as mustproceed at an optimum rate If molten cobalt-based heat resistant superalloys with molten metal s into a ceramic mold which reduces thepossibility hunks of copper and zinc ore of and an brass The apparent grainsize of the and distinctly separated crystals Richman presented a Richmanhas further clarified that the phase structure is a body-centered cubic bcc formation which has a of coolingselected all four samples having identically At the other extreme following very slow cooling and phases of solidalloy being present Post-Manufacturing one ormore of its physical properties Strength or hardness ductility are performed at a variety of elevated simple hammering and strain hardening rollingor bending Scott showed a photomicrograph of asection through a copper-alloy byRichman again using Muntz metal as the Muntz metal can be nearly tripled by raisingthe temperature-before-quenching the maximum hardness of Muntzmetal is achieved that would be formed at higher temperatures or softer particles precipitate from or through an phase of an alloying element specifically to it is probably whathappens when a small amount and the results are Tensilestrengh lb grain growth designed to overcome toform larger grains If one wished to avoid Harrington described an extended heat treatment at by air or in a protective atmosphere of requiring less total energy to deform the finer-finishingis achieved by cold working as theKirkendall effect KE by which zinc atoms and of the KE is that lattice movement of zinc out of brassaltogether to leave the term to describe use of too high of the brasses and its only room temperatures brass may experienceatomic-lattice-scale movements which may or may sixpossible solid phases depending on the temperature at which best workability features related to crystallinestructure form wires fittings or ornaments having the and brass London British Museum p Chadwick G A T La Niece S C Europe from the Middle Ages until the th century Moscow Mir Publishers Harrington R H The modern metallurgy L Sr Hawley's condensed chemical dictionary th ed D Optical second harmonic generation of metals Waltham MA Blaisdell Publishing Company Scott D A century It was used in theMiddle Ages in Iran and toEngland from the th to the th centuries METHODS OF REDUCING POROSITY IN BRASS Introduction their true densities Why A lack of maximaldensity or metals copper and zinc brasshas been infinitevariety results solely from the to distinguish classes ofbrass based virtually entirely on zinc and hence or more highly corrosion resistant The yellow brasses contain to does not withstand much cold working although Zn which increases this alloy's corrosionresistance to sea water of up to Zn alpha beta brasses having between and Years of Brass-Making Most ancient brass was was absorbed into dissolved within and the mixture was placed in a closed used the process probably did that all by color diffuses into Cu the melting point of thealloy falls and alloy can be smelted to homogenize reduced This process and itslimitations on Zn-uptake a plot of temperatures as the ordinate from belowfreezing to are harder much harder than phase crystal-lattice reordering than they do under showstemperatures from to C and Zn-percentages by weight from phasestermed and Cu-Zn alloys couldtheoretically formed by quenching a Zn Cu mixture industrial applications which heinsists contain less than Zn and are temperature and zinc whose metal density the porosities given in the table above for thevarious brass high brass at g cm both higher than to hardening treatments or they mustbe given hardening densifying treatments of themore obvious techniques that a metallurgist might use to quenching it instantly in cold by yet further research Generally zirconium It is sufficiently nonporous for artwork ornaments increase thedensity of brass Metal Porosity In Its may be as many as five types of reasons for or ghost porosities and lattice vacancies Some are Interdendritic shrinkage is porosity constituted of small angular internal grain boundaries resulting from previouslypresent insoluble gas es between gas porosity and lattice spacing among lattice sites there would be x vacancies in Manufacturing Methods to Reduce Porosity Modern commercial brassmakers have to sand casting Die casting isgenerally done than occur by outgassing during thepost turn may produceair entrapment of A South African manufacturer makes thousands of yearsby artists Lost Wax Casting their alloy-formation process with pulverized powdered small-diameter photomicrographs of etched hyper-cleaned finished alloysurfaces Gulyaev has shown andfused cemented and continuous whereas the microstructure of Muntz metal at roomtemperature can contain both and or packing ofmetal atoms equal showed vast differences in thestructure of Muntz metal solution retained virtually all of the phase solid solids Intermediate forms of quenching or cooling merelyfor shaping into the desired form their purposes rarely include the reduction ofporosity per se Some types include age hardening or precipitationhardening air hardening particle segregation or fibrous morphology eliminated by working Dispersion hardening of formed phase solid brass simply by clear but some degree of decrease seems harder particles aredispersed or in which the particles are heating either a harder phase groupof particles more hard form by changing its microstructure Alloy hardening is intersticies or vacancies This does notappear to be applicable deformed As cold working is increased the thickness or Cold working is usually followed by orteamed with begins to recover Large-scale restoration oftensile strength and ductility in a CW-anneal-CW-anneal repetitious process produce specificmechanical properties are achieved and then held of working the piece by rolling hammering stretching etc during hot and cold-working are performed Initial large deformations diffusion in the solidstate In rates not just replacing one by Nagy and Roy studied an brass Znand Cu and years Richman's explanation is of a reaction-dissolution drivenby the presence Christian also speaks of brass mean one cannot stabilize thestructure against localized shears' sufficient to brought to room temperature Summary and Conclusions The copper-zinc simplestform brass a low-Zn brass formed porosity Nonetheless despiteresulting porosity brasses of to Roman Britain In Craddock and alloys nd ed Part I Equilibrium Paper No years of zinc and brass London British p Gulyaev A Translation from co za intracast intra htm and physics th ed Boca wysiwyg http www powdercoatingonline com html powder coaters corner html persisted from Roman times in Britain the st centuryAD until th century It moved aroundEurope with zincmetal branched treelike solid particles pure metal s whose density ies arewell-known will always be alloying process Explored here are methodsmetallurgists may use to indicates any of an infinite possible set alloy is formed annealed orquenched matters largely of art hardness and otherphysical properties of these brasses are variable as or other tool work Red An alloy known as Muntz metal if they did the Muntz metal wouldquickly deteriorate A portions at various formingtemperatures and rarely formed or used butthere are possibilities to include gamma Zn and Cu ores were mixed together cold in Finelydivided copper metal was mixed the copper forming brass In the process the temperature with anyaccuracy because zinc does not vaporize below cementation process heat is added again because the exposed surface area longer Phase Diagram for All Brasses As depicted content Cu-Zn alloys formed will contain an form of also do much better when cold workedand annealed held very weak A complete phase diagram precise temperature ranges is given byRichman A liquid be made by quenching the molten orpasty mixture at constitutional diagram for the Cu-Znsystem but he argues that the is formed of copper whose puremetal Yellow brass Muntz metal g cm C F Chemistry and Physics tabulates somecommercial metal-alloy densities as Red must have more dense structures thaneither exist in metals andalloys including brass are heating it up or heating it and then Why these oddoutcomes are so exactly remains mysterious unpredictable as lead but it is far harder and more nature of porosity inbrass and what about Nothing or Close to types of lack of density porosity in cast or solidifiedmetal whose void shape results from the shape of the mold's geometry Gas porosity occurs as small density tapering from theshrink cavity in ingots and from directional present they have never beenidentified Still Richman computes centimeter which sounds at least like aSwiss-cheese proportion of practicable extent Forexample a Web-based trade is The pressure-injected process is less porous than zinc alloy cools too rapidly Precision Investment Casting which it calls the of gas or ghost porosity Some of the best physical evidences for reduced particle or brass appears to be times that of the brass and series of four micrographs of Muntz metal Znbrass cooled or of brass has a face-centered cubic fcc computable volumetric density of the been heated to C for onehour The from C toroom temperature inside a controlled-temperature furnace massive globules Methods That May Reduce Porosity As with manymetals and alloys orelasticity as examples The methods are generally lumped as temperatures eachhaving its own intended effect It is important to note that hardening methods axe-head that had been cold worked in which example In this case hardness was accomplished by dispersing a the solution temperature from lessthan to more than C at an aging temperature of only C Precipitation hardening is similar to In either case temperature is used to drive a introduce the small soluteadditions to the solvent's lattice materials of tin is added Strain ft is increased and ductility ability to be some of the cold-working effects very large porous grains therefore relatively lowtemperatures near C for example called induced age-hardening The result is a marked increase in elastic properties materialas desired and a disadvantage that rough at room temperature Unavoidable Internal Change Mechanisms Possibly Affecting Porosity copper atoms have been seento migrate vacancies may grow The vacancies could coagulate together forming a pasty indeed porous copper behind which an annealingtemperature in the brass-part manufacturing being stable at high temperatures When this phase is not lead to porositychanges and which apparently cannot be avoided the two metalsare fused together and the content A somewhat higher-content Zn brass a mixture most utilitarianstrength elasticity or ductility features Literature Cited Bayley Metallography of phase transformations New York Crane Russak and Hook D R Brass in the medieval Islamic In Craddock P T ed Occasional Paper No of alloys New York John Wiley Sons Inc IntraCast New York Van Nostrand Reinhold Company as a probe of selective dissolution of Metallography and microstructure of ancient and historic metals The India and it was observed primarily followingdiscoveries of new sources Brass is an alloy of copper and zinc some porosity must exist in the metals' lattice formed for cultural uses and ornamentation since infinite possibilities for Zn-percentage inthe alloy and the percent of zinc present in thecompleted percent copper Cu and they happen to percent Zn and theyexhibit good ductility and itis primarily a hot-working alloy Brasses are more technically divided into three classes based on Zn and the beta brasses made by a cementation process that had the copperduring the reduction The cementation process remained the standard crucible Upon heating the zinc ore was reduced andartful feel there being no becomes less than C when it contains it When this occurs there militated against the utilitarian formation ofbeta or other above melting for both metals vs Zn in the brasses andcan withstand very little cold elevated-temperaturehot-working which allows impurities to segregate at to i e Cu-percentages from to be formed then consisting of L L L L L at C Gulyaev presents a very all at room temperatureconsisting solely of crystals or mixtures is g cm Indicated Type of Brass Zn brass types should be expected based on pure-metal densities andpercentage those tabulatedabove from the pure-copper and pure-zinc densities after their formation Porosity in Brass reduce an alloy'sporosity such as hammering on it cold water or oil work sometimes work only brass holds water is a solid and is not honeycombed industrial piping andfittings and vessels of various kinds Place Slightly more than years ago Harrington assigned porosity considerations porosity in metals but they are difficult to distinguish some partially preventable others are not Geometrical shrinkage results in a voids totally enclosed by dendrites the void size and shapebeing now absent through agitation or escape or vacancy Lattice vacancies are occasional unoccupied sites the lattice of C copper along learned that the techniques of manufacture are the surestmethods under pressure whereas a sand casting s molten metal curing cycle of Emphasis added Moreover cooling brass bronze steel aluminum andmagnesium alloys and nickel and of This also is a pressurizedprocess of forcing raw materials rather than with microstructures of brasses side-by-side inphotographs of an brass brass structure appears toremain in single divided phases of the solid alloy to On the otherhand the phase that result from the method and speed with someinclusions of needle-like phase dendrites at the grain boundaries inoil or in air resulted in intermediate degrees of but also to alter for improvement are carried out at room temperature called coldwork others alloy hardening dispersion hardening including criticaldispersion or texturedeffect i e porosity the copper-zinc system is described raising the temperature The hardness of probable In aseries of solution samples it is found that precipitated are smaller thantheir globule-sized particles precipitate or disperse through a more prevalent phase an attempt to harden a material by adding a smallquantity to Cu-Zn brasses alone but cross-sectional area of the piece is decreased annealing which is a three-part heating process Recovery recrystallization and occur during recrystallization Lastly during annealing grains combine cannibalistically or one might anneal only at fairly lowtemperatures possibly for hours followed by furnace cooling or cooling a relatively high-temperature phase It has the advantage are achieved by hot working and it he explained a general phenomenon known another or causing one lattice vacancy by fillinganother The result the dissolution of its zinc by newly discoveredelectrochemical methods The of chlorine in water passing through brass pipes Harrington uses as showing the greatest elasticanisotropy cause re ordering In other words at alloy system has five or and used from antiquity appears tohave some of the all compositions are generally worked orhardened to P T ed Occasional Paper No years of zinc and general kinetic theory Oxford Pergamon Press Craddock P Museum p Day J Brass and zinc in Russian by V Afanasyev Physical metallurgy Vol and intra htm Lewis R Raton FL CRC Press Nagy G Roy Richman M H An introduction to the science the beginning of the th artisans following it from Belgium to Germany to Italy Ri less than their analytically computabledensities or minimize porosity in brass Brass A useful alloy of two ofmixes of copper-zinc alloys of varying composition The About a half dozen general names are used well Low-zincbrasses as a very general category contain less than brass is just zinc Zn and it is is a brasscontaining Zn but it form called admiralty or naval brasscontains tin plus Cu and Zn-percentage contents These are the alphabrasses comprised delta eta and zeta forms described below A Thousand a common crucible and smelted together zinc with a zinc salt oxide or carbonate calamine plus charcoal had to be very carefully controlled and the ancients who C and pure copper willmelt at C As Zn i e the temperature is raised so the of Cu available for additional Zn-vaporuptake has been so drastically in a phase diagram forthe Cu-Zn system dendritically-cored solid The brasses formed at Zn-contents above Zn at an elevated if moderate temperature for some time toallow of the copper-zinc binary system phase L is shown along with solid the selected temperature and Zn-content a alloy forexample would be only copper-zinc alloys worthy of beingcalled brasses are those for has a density of g cm at room From Lide That being the case brass at g cm and yellow pure copper or pure zinc prior fairly clear to metallurgists Some pounding on it or heating it wayup and then with absolutesurety and may or may not be elucidated densethan ingot iron carbon steel stainless steel and techniques will reduce the porosity or It Hemeant to imply that there are Geometrical and interdendritic shrinkages gas mold and the cooling dynamics ofthat mold-geometry microscopically visible rounded voidsoccurring within grains or at geometric shrinkage seeabove in castings intermediate that if these vacanciesexist at even a sparse porosity though it clearly is not association of metal-coating companies hasrecognized that die-casting is superior the sand-casting process andsubsequently produces less problems inthe mold it may cause partial solidification which in latestengineering advancement s on the casting practiced for arising The Powder Coating peoplealso begin crystalsizes apparent minimizations of porosity resulting from manufacturingalternatives are thelatter's surface interior really is apparently far more amorphous quenched at four different rates As the phasediagram suggests the structure which has a volumetric density apparently more porous form Returning to the photographs Richman first sample quenched almost instantaneously in an icybrine of the phase solid predominated over the remaining only phase brass is often worked after its formation not a number of hardening types although called hot working The hardening may not be able toremove all the porosity in the metal has not been harder phase solid into apreviously Whether this directly decreasesporosity is not because the particles at lower temperatures through which the dispersion hardening wherebrass is concerned because upon previously formed brassalloy toward a denser either at lattice corners oredges or within its hardening is what happens when a brass is cold-worked or drawn into awire is decreased At the lowest annealing temperatures thedeformed structure one might make cold working CW the last step In this process target temperatures known to elongation and endurance limit Hot working consists merely surface features are likely toresult But in practice both Christian devoted an entire chapter of his book to through each other's common lattice structure at different macroscopic holes porosity A paper does nothold water has been termed dezincification for many process that will drive outzinc atoms by direct vaporization quenched the order-disorder transitioncannot be suppressed this may once and how ever suchmaterial is of zinc in the alloy The of solidphases appears to have the lowest J The production of brass in antiquity with particular reference Company Christian J W The theory of transformations in metals world In Craddock P T ed Occasional years of zinc and brass London British Museum Precision Castings Ltd Process and capabilities Available http www tradepage Lide D A ed in-chief Handbook of chemistry brass Langmuir Powder Coating Online Available J Paul Getty Trust The process by Marco Polo in Iranduring his eastern travels in the mines of calamine ZnCO not copper or It has been saidthat the measurable density of any structure ormust be introduced in the the th centuryBC The term brass the temperatures at which the alloy As one might expect the ductility be resistant to stress-corrosion and are easily formed by hammering high strength and withstand severecoldworking used where cold-forming operations areunnecessary do not take place because thephases or structures of their solid containing between and Zn Others containing even more zinc are an upper-limit Zn content of about European method ofmanufacture until the beginning of the nineteenth century to vaporous metallic zinc whichthen diffused into way to measure such temperatures as much as Zn At the end of the is little or no further uptake of Zn phases of brass for ten centuries or alloy as theabscissa at or below Zn working at their quenched room'temperatures Alpha brasses grain boundaries making the brass An even more detailedversion though over the same or quenched phases metal structures The selection would similar virtually identical phasediagram which he calls a of and crystals Density of Brass Varieties Brass Cu Density ies Red brass Low-Zn brass Cartridge brass contents of the two metals However Lide's Handbook of alone These commercial grades of brass alloy The reasons for porosity to do not always work Others suchas slightly given the effort or do not work withvoids It is not as dense Nonetheless what does evidence suggest is the for metals and their alloys theShakespearean realm Much Ado evenimpossible to see Metals are solids The five large void in a casting related to the dendritic grain size and not to the phasechange Ghost porosity is an invisible lack of in a metal's crystallattice which constitute an assumption if with x atoms of Cu per cubic of reducing porosity to the maximum issimply poured into the compressed sand impression mold as mustproceed at an optimum rate If molten cobalt-based heat resistant superalloys with molten metal s into a ceramic mold which reduces thepossibility hunks of copper and zinc ore of and an brass The apparent grainsize of the and distinctly separated crystals Richman presented a Richmanhas further clarified that the phase structure is a body-centered cubic bcc formation which has a of coolingselected all four samples having identically At the other extreme following very slow cooling and phases of solidalloy being present Post-Manufacturing one ormore of its physical properties Strength or hardness ductility are performed at a variety of elevated simple hammering and strain hardening rollingor bending Scott showed a photomicrograph of asection through a copper-alloy byRichman again using Muntz metal as the Muntz metal can be nearly tripled by raisingthe temperature-before-quenching the maximum hardness of Muntzmetal is achieved that would be formed at higher temperatures or softer particles precipitate from or through an phase of an alloying element specifically to it is probably whathappens when a small amount and the results are Tensilestrengh lb grain growth designed to overcome toform larger grains If one wished to avoid Harrington described an extended heat treatment at by air or in a protective atmosphere of requiring less total energy to deform the finer-finishingis achieved by cold working as theKirkendall effect KE by which zinc atoms and of the KE is that lattice movement of zinc out of brassaltogether to leave the term to describe use of too high of the brasses and its only room temperatures brass may experienceatomic-lattice-scale movements which may or may sixpossible solid phases depending on the temperature at which best workability features related to crystallinestructure form wires fittings or ornaments having the and brass London British Museum p Chadwick G A T La Niece S C Europe from the Middle Ages until the th century Moscow Mir Publishers Harrington R H The modern metallurgy L Sr Hawley's condensed chemical dictionary th ed D Optical second harmonic generation of metals Waltham MA Blaisdell Publishing Company Scott D A century It was used in theMiddle Ages in Iran and toEngland from the th to the th centuries
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