Effects of alloying additions
Free machining brasses
High tensile brasses
Effect of processing on properties
Effect of zinc content on properties
Castability
Available forms and properties
Monday, March 10, 2008
Forms of Brass
Describes the extensive range of shapes and sizes available and the way in which they can be made. There is also coverage of the old British standards and material designations and the EN standards and designations which have replaced them.
Extrusions
Hot stampings
Forgings
Wire
Sheet and strip
Tube
Plate
Castings
Ordering Information
Case histories
Extrusions
Hot stampings
Forgings
Wire
Sheet and strip
Tube
Plate
Castings
Ordering Information
Case histories
Why Make it in Brass?
Explains the very wide variety of combinations of properties unique to brasses that make them the most cost-effective materials to select for the manufacture of a vast range of products.
Cost-effectiveness
Low cost manufacturing
Corrosion Resistance
Machinability
Cost-effectiveness
Low cost manufacturing
Corrosion Resistance
Machinability
Sunday, March 09, 2008
Overview of Brass
Brasses are copper zinc alloys. In general, they have good strength and corrosion resistance, although their structure and properties are a function of zinc content. Alloys containing up to approximately 35% zinc are single phase alloys, consisting of a solid solution of zinc and alpha copper. These brasses have good strength and ductility, and are easily cold worked. The strength and ductility of these alloys increases with increasing zinc content. The alpha alloys can be differentiated by a gradual change in color, from golden yellow to red, as the zinc content is increased up to 35%. Gilding 95%, Commercial Bronze, Jewelry Bronze, Red Brass and Cartridge Brass are in this category of brasses. These are known for their ease of fabrication by drawing, high cold worked strength and corrosion resistance. Increasing the zinc content up to 35 % produces a stronger, more elastic brass alloy with a moderate decrease in corrosion resistance. Brasses containing between 32 and 39% zinc have a two phase structure, composed of alpha and beta phases. Yellow brasses are in this intermediate category of brasses. Brasses containing more than 39% zinc, such as Muntz metal, have a predominantly beta structure. The beta phase is harder than the alpha phase. These materials have high strengths and lower ductility at room temperature than the alloys containing less zinc. The two phase brasses are easy to hot work and machine, but cold formability is limited. Brasses are used in applications such as blanking, coining, drawing, piercing, springs, fire extinguishers, jewelry, radiator cores, lamp fixtures, ammunition, flexible hose, and the base for gold plate. Brasses have excellent castability, and a good combination of strength and corrosion resistance. The cast brasses are used in applications such as plumbing fixtures, fittings and low pressure valves, gears, bearings, decorative hardware and architectural trim. The UNS designations for wrought brasses includes C20500 through C28580, and C83300 through C85800 for cast brasses.
Certain brasses can corrode in various environments. Dezincification can be a problem in alloys containing more than 15% zinc in stagnant, acidic aqueous environments. Dezincification begins as the removal of zinc from the surface of the brass, leaving a relatively porous and weak layer of copper and copper oxide. The dezincification can progress through the brass and weaken the entire component. Stress corrosion cracking can also be a problem for brasses containing more than 15% zinc. Stress corrosion cracking of these brasses occurs when the components are subject to a tensile stress in environments containing moist ammonia, amines, and mercury compounds. If either the stress or chemical environment is removed the stress corrosion cracking will not occur. Sometimes a stress relieving treatment is sufficient to prevent stress corrosion cracking from occurring. The microstructure of the single phase brass alloys, with up to 32% zinc, consists of a solid solution of zinc and alpha copper. The as-cast structure of the low zinc brasses consists of alpha dendrites. The first material to solidify is almost pure copper, as the dendrites continue to solidify they become a mixture of copper and zinc. A composition gradient exists across the dendrite, with zero zinc content at the center and highest zinc content at the outer edge. The composition gradient is called coring, and it typically occurs with alloys that freeze over a wide temperature range. Subsequent working and annealing breaks up the dendritic structure. The resulting microstructure consists of twinned, equiaxed grains of alpha brass. The annealed microstructure is made up of equiaxed, twinned grains of alpha copper, similar to the structure of unalloyed copper. The grains appear in different shades due to their different orientations. The twins are parallel lines that extend across individual grains. The twins result from a fault in the staking sequence of the copper atoms, making it difficult to distinguish the individual grains.
Alpha copper is the primary phase in cast alloys containing up to approximately 40% zinc. The beta phase,which is the high zinc phase, is the minor constituent filling in the areas between the alpha dendrites. The microstructure of brasses containing up to approximately 40% zinc consists of alpha dendrites with beta surrounding the dendrites. The wrought materials consist of grains of alpha and beta. Cast alloys with greater than 40% zinc contain primary dendrites of beta phase. If the material is fast-cooled, the structure consists entirely of beta phase. During a slower cool, the alpha precipitates out of solution at the crystal boundaries, forming a structure of beta dendrites surrounded by alpha. This structure is called a Widmanstatten structure, because a geometrical pattern of alpha is formed on the certain crystallographic orientations of the beta lattice. The wrought, two phase material consists of grains of beta and alpha. Hot rolling tends to elongate the grains in the rolling direction.
Brasses frequently contain lead in order to improve machinability. The microstructure of the leaded brasses is similar to that of the unleaded brasses with the addition of almost pure lead particles found in the grain boundaries and inter-dendritic spacings. The lead is observed in the microstructure as discrete, globular particles because it is practically insoluble in solid copper. The number and size of the lead particles increases with increasing lead content.
Certain brasses can corrode in various environments. Dezincification can be a problem in alloys containing more than 15% zinc in stagnant, acidic aqueous environments. Dezincification begins as the removal of zinc from the surface of the brass, leaving a relatively porous and weak layer of copper and copper oxide. The dezincification can progress through the brass and weaken the entire component. Stress corrosion cracking can also be a problem for brasses containing more than 15% zinc. Stress corrosion cracking of these brasses occurs when the components are subject to a tensile stress in environments containing moist ammonia, amines, and mercury compounds. If either the stress or chemical environment is removed the stress corrosion cracking will not occur. Sometimes a stress relieving treatment is sufficient to prevent stress corrosion cracking from occurring. The microstructure of the single phase brass alloys, with up to 32% zinc, consists of a solid solution of zinc and alpha copper. The as-cast structure of the low zinc brasses consists of alpha dendrites. The first material to solidify is almost pure copper, as the dendrites continue to solidify they become a mixture of copper and zinc. A composition gradient exists across the dendrite, with zero zinc content at the center and highest zinc content at the outer edge. The composition gradient is called coring, and it typically occurs with alloys that freeze over a wide temperature range. Subsequent working and annealing breaks up the dendritic structure. The resulting microstructure consists of twinned, equiaxed grains of alpha brass. The annealed microstructure is made up of equiaxed, twinned grains of alpha copper, similar to the structure of unalloyed copper. The grains appear in different shades due to their different orientations. The twins are parallel lines that extend across individual grains. The twins result from a fault in the staking sequence of the copper atoms, making it difficult to distinguish the individual grains.
Alpha copper is the primary phase in cast alloys containing up to approximately 40% zinc. The beta phase,which is the high zinc phase, is the minor constituent filling in the areas between the alpha dendrites. The microstructure of brasses containing up to approximately 40% zinc consists of alpha dendrites with beta surrounding the dendrites. The wrought materials consist of grains of alpha and beta. Cast alloys with greater than 40% zinc contain primary dendrites of beta phase. If the material is fast-cooled, the structure consists entirely of beta phase. During a slower cool, the alpha precipitates out of solution at the crystal boundaries, forming a structure of beta dendrites surrounded by alpha. This structure is called a Widmanstatten structure, because a geometrical pattern of alpha is formed on the certain crystallographic orientations of the beta lattice. The wrought, two phase material consists of grains of beta and alpha. Hot rolling tends to elongate the grains in the rolling direction.
Brasses frequently contain lead in order to improve machinability. The microstructure of the leaded brasses is similar to that of the unleaded brasses with the addition of almost pure lead particles found in the grain boundaries and inter-dendritic spacings. The lead is observed in the microstructure as discrete, globular particles because it is practically insoluble in solid copper. The number and size of the lead particles increases with increasing lead content.
Overview of Copper
The major uses of pure, unalloyed copper are based on its high electrical and thermal conductivity as well its good corrosion resistance. Almost all alloying elements are detrimental to the electrical conductivity of copper, making the purity of the mental an important issue. Commercially pure copper is represented by UNS numbers C10100 to C13000. The various grades of unalloyed copper differ in the amount of impurities and therefore do behave differently. Oxygen free coppers are used in applications requiring high conductivity and exceptional ductility.
The pure copper or high copper alloys are made from copper ores that are obtained from the mines as sulfides, which contain zinc, lead and other sulfur. The ores are crushed and milled until they becomes a powder. A technique known as flotation separates the metal from the non-metal components of the powder. The next step is a concentrating stage where minerals are concentrated into a slurry that is about 15% copper. The copper is then melted and purified in several stages until it is 99% pure copper. At this point it is cast into anodes. Oxygen remains in the structure as cuprous oxide, Cu2O. The majority of the structure is pure copper. The copper metal solidifies from the liquid state by the growth of crystals. The crystals grow in preferred directions and form open, tree like structures called dendrites. The dendritic structure is very typical of cast metals. A lower melting point mixture of pure copper and cupprous oxide, called a eutectic, forms in the open spaces between the dendrites. The eutectic particles are usually dark, globular bodies dispersed in a copper background. The cuprous oxide particles form a network, outlining the dendritic cells. Pores, seen as dark spots in the microstructure, are also present in the as-cast material.
The copper anodes are then refined electrolytically to 99.9% purity. Copper melted under non oxidizing conditions is called oxygen free copper. The most popular form of pure copper is the standard electrical wire grade of copper (C11000) contains 99.95% Cu, 0.03% O2, and less than 50 ppm metallic impurities. It has a high electrical conductivity, in excess of 100% IACS. In the as cast form it is called electrolytic tough pitch (ETP) copper. The structure of the as-cast material is similar to that described above. When the as-cast ETP copper is hot rolled the eutectic structure is completely destroyed. The microstructure of the hot rolled copper contains many small grains. Parallel straight lines extending across many of the grains are called annealing twins. They appear after a metal has been mechanically worked at a high temperature, called annealing, and deformed. The interdendritic network of cupprous oxide particles was destroyed by hot rolling. After hot rolling, cupprous oxide particles changed form, and are present as stringers or aligned rows of dark particles. The oxide particles are much larger and fewer in number than in the as cast microstructure.
The pure copper or high copper alloys are made from copper ores that are obtained from the mines as sulfides, which contain zinc, lead and other sulfur. The ores are crushed and milled until they becomes a powder. A technique known as flotation separates the metal from the non-metal components of the powder. The next step is a concentrating stage where minerals are concentrated into a slurry that is about 15% copper. The copper is then melted and purified in several stages until it is 99% pure copper. At this point it is cast into anodes. Oxygen remains in the structure as cuprous oxide, Cu2O. The majority of the structure is pure copper. The copper metal solidifies from the liquid state by the growth of crystals. The crystals grow in preferred directions and form open, tree like structures called dendrites. The dendritic structure is very typical of cast metals. A lower melting point mixture of pure copper and cupprous oxide, called a eutectic, forms in the open spaces between the dendrites. The eutectic particles are usually dark, globular bodies dispersed in a copper background. The cuprous oxide particles form a network, outlining the dendritic cells. Pores, seen as dark spots in the microstructure, are also present in the as-cast material.
The copper anodes are then refined electrolytically to 99.9% purity. Copper melted under non oxidizing conditions is called oxygen free copper. The most popular form of pure copper is the standard electrical wire grade of copper (C11000) contains 99.95% Cu, 0.03% O2, and less than 50 ppm metallic impurities. It has a high electrical conductivity, in excess of 100% IACS. In the as cast form it is called electrolytic tough pitch (ETP) copper. The structure of the as-cast material is similar to that described above. When the as-cast ETP copper is hot rolled the eutectic structure is completely destroyed. The microstructure of the hot rolled copper contains many small grains. Parallel straight lines extending across many of the grains are called annealing twins. They appear after a metal has been mechanically worked at a high temperature, called annealing, and deformed. The interdendritic network of cupprous oxide particles was destroyed by hot rolling. After hot rolling, cupprous oxide particles changed form, and are present as stringers or aligned rows of dark particles. The oxide particles are much larger and fewer in number than in the as cast microstructure.
What is RoHS ?
The RoHS Directive stands for "the restriction of the use of certain hazardous substances in electrical and electronic equipment". This Directive bans the placing on the EU market of new electrical and electronic equipment containing more than agreed levels of lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants. Manufacturers need to understand the requirements of the RoHS Directive to ensure that their products, and their components, comply.
Non-ferrous prices and currency affects indian import
Copper as base metal in LME (London Metal Exchange) moving towards its life high. Improving a little appreciation of US$ and Euro against Indian currency cause the raw-material scrap costs high. Euro has achived its life time high against Indian Rupees as 62.50 per euro. In terms of import from european country in costiler comparetaly to other neighbour countries.
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