Presentation on theme: "Copyright Joseph Greene 2002 All Rights Reserved 1 Chapter 9. Phase Diagrams_ Equilibrium Microstructure Development Phase Rule Phase Diagram Lever Rule."— Presentation transcript:
Copyright Joseph Greene 2002 All Rights Reserved 1 Chapter 9. Phase Diagrams_ Equilibrium Microstructure Development Phase Rule Phase Diagram Lever Rule Microstructural Development During Slow Cooling
Copyright Joseph Greene 2002 All Rights Reserved 2 Phase Rule Phase rule –Identifies the number of microscopic phases associated with a given state condition, a set of values for temperature, pressure and other variables that describe the nature of the material. Phase –Chemically and structurally homogeneous portion of the microstructure. Single phase can be polycrystalline (Fig 9-1), but each crystal grain differs only in crystalline orientation or chemical composition. Component –Distinct chemical substance from which a phase is formed. Example, Copper and nickel are so similar in nature that they are completely soluble in each other in any alloy proportions. –There exists a single phase (solid solution) with two components. Example, Compounds can be components –MgO and NiO form solid solutions similar to Cu Ni with one phase. Example, Two components can form distinct phases each richer in a different component. –Perlite structure forms from alternating structures of ferrite and cementite –Fig 9-2. Ferrite is -Fe with a small amount of cementite in solid solution. Cementite is nearly pure Fe 3 C. Components are Fe and Fe 3 C.
Copyright Joseph Greene 2002 All Rights Reserved 3 Phase Rule Degrees of freedom –Number of independent variables available to the system Example, pure metal at its melting point has zero degrees of freedom. –At this condition, or state, the metal exists only in two phases in equilibrium, that is solid and liquid phases simultaneously. –Any change in temperature will change the state of the microstructure »If temperature is raised, all of the solid phase will melt and become the liquid state. »If temperature is lowered, all of the liquid phase will solidify and become the solid state. –State (processing) variables to control microstructure Temperature, pressure, and composition –Relationship between microstructure and state variables Pressure is very small relationship at most processing conditions
Copyright Joseph Greene 2002 All Rights Reserved 4 Phase Rule Gibbs Phase Rule –Relationship between microstructure and state variables –F = C – P + 1 (Most common equation for most processes) F = degrees of freedom, C = number of components, P = number of phases, 1 = state variable is temperature –Example, Pure metal at its melting temperature C = 1 component, P = 2 phases (solid and liquid), F = 1 – 2 + 1 = 0 Degrees of freedom is zero. This means we can change the two phases (solid and liquid) by varying the temperature. –Example, metal with a single impurity at its melting point, solid and liquid phases can usually coexist over a range of temperatures. C = 2 components, P = 2 phases; F = 2 –2 + 1 = 1, Have One independent variable. Single degree of freedom means we can maintain the 2 phase microstructure while we vary the temperature of the material. By changing the temperature, we indirectly vary the composition of the individual phases. Composition is a dependent variable Josiah Gibbs (1839-1903) –American Professor of mathematical physics at Yale University –Known as quiet individual who is the biggest pioneer in thermodynamics. Phase rule is the cornerstone of thermodynamics (relationship between matter and energy) Thermodynamics is the basis for air conditioning, pumps, heaters, anything that has liquid and gas combinations.
Copyright Joseph Greene 2002 All Rights Reserved 5 Phase Rule Phase diagram –A map that helps explain the microstructure that exists at a certain temperature and pressure and composition. –Example, Water phase diagram. Fig 9-3 The one component diagram summarizes The phases present for water as a function of T and P –F = 1 – 2 – 1 = 0 »If change temperature, then can get solid or liquid For a fixed pressure of 1 atm (14.69 psi), –Water at room temperature 25 C is liquid, »at T= 100 C is gas and at 0 C is solid. –Example, Pure iron Fig 9-4 Can be in a different crystalline structure (phase) - iron - iron is austenite - iron is ferrite –F = 1 – 2 – 1 = 0 »If change temperature, then can get solid or liquid Temp Press Gas Liquid Solid 1 atm 100 C 0 C Temp Press Gas Liquid Solid 1 atm 1538 C 910 C austenite ferrite
Copyright Joseph Greene 2002 All Rights Reserved 6 Phase Diagram Phase diagram is any graphical representation of the state variables associated with microstructures through Gibbs phase rule. –Phase diagrams are used for binary (2 Component; C= 2) and ternary diagrams (3 component systems; C=3) –Phase diagrams are maps of the equilibrium phases associated with the various combinations of temperature and composition. Concern is to change phases and associated microstructure that follow changes in temperature and composition. Complete Solid solution –Simple binary solution is two species that are completely soluble in each other in both liquid and solid states. Cu and Ni are completely soluble; MgO and NiO are completely soluble; Fig 9-5 Phase diagram –Melting points of A and B –For high T of any composition will give a liquid –A and B are completely soluble in liquid phase field, L –A and B are completely soluble is solid solution (SS) –Intermediate temperature has liquid plus solid solution Temp Composition L + SS Liquidus Solidus 0 20 40 60 80 100 Melting Point of A AB 100 80 60 40 20 0 A Rich B Rich
Copyright Joseph Greene 2002 All Rights Reserved 7 Phase Diagram Complete Solid solution –Compositions of A and B are read of x- axis –Compositions of liquid and solid solution are Are read from x-axis by –Overall composition of SS and liquid, X –Composition of SS is SS –Composition of Liquid is L Horizontal line connection the two phase compositions is termed tie line. Relative amounts of each phase with lever rule –Gibbs phase rule: F = C – P +1 For melting points of pure material, F = 0 –Invariant point. Change T, changes to liquid or solid For 2 phase region (L+SS), F = 1, –Change in T results in composition changes by lever rule For Liquidus and solidus areas the F = 2, –Change in T or composition does not change basic nature of microstructure Temp Composition L + SS Overall composition of A and B Solidus 0 20 40 60 80 100 Melting Point of A AB 100 80 60 40 20 0 Temp Composition F = 2 –2 + 1 =1 Solidus 0 20 40 60 80 100 Melting Point of A AB 100 80 60 40 20 0 x LSS Liquid F = 2 –1 + 1 =2 F = 0 F = 2 –1 + 1 =2 Liquidus
Copyright Joseph Greene 2002 All Rights Reserved 8 Phase Diagram Inorganic material use Phase diagrams Materials that are soluble –Metals and ceramics systems Fig 9-9 Cu –Ni complete solid solution Variety of Cu-Ni alloys fall within system, Monel NiO-MgO system is a ceramic system –Structure has similar cations in solid solution –Note: composition axis for NiO-MgO Composition Temp, C Temp, C L + alpha Overall composition of A and B Alpha phase 0 20 40 60 80 100 CuNi 100 80 60 40 20 0 x LSS Liquid 1100 1500 Composition Mole% MgO L + SS Solid Solution 0 20 40 60 80 100 NiOMgO Liquidus 2800 2000
Copyright Joseph Greene 2002 All Rights Reserved 9
10 Phase Diagram Inorganic materials that are insoluble –Metals and ceramics systems Fig 9-1. Binary systems that the components are not soluble –At low temperatures there is two-phase field for pure solids A + B. –Solidus (solid solution) is the horizontal line that corresponds to eutectic Temp »Temperature at which liquid cools to solid at the composition. »There are no solids is liquid state and no liquids in solid state at the composition »This is the only composition that the liquid material cools to a solid without any other phases present Fig 9-12 Relative microstructures for binary eutectic diagram. –Liquid + solid microstructures –Layered structure of A & B in eutectic Temp, C Composition Fig 9-1 Solidus A+B 0 20 40 60 80 100 AB Liquid, L A + L B + L Temp, C Composition Fig 9-12 Eutectic Layered A+B 0 20 40 60 80 100 AB Liquid, L Crystallites of B in matrix L2 Crystallites of A in matrix L1
Copyright Joseph Greene 2002 All Rights Reserved 11 Phase Diagram Eutectic diagram with limited Solid Solution –For many binary systems, two components are partially soluble Fig 9-14 shows eutectic diagram with limited solid solution Two solid-solution phases, and , are distinguishable Each component will have a crystal structure –Each component serves as a solvent for the other impurity component »Example, consists of B atoms in solution in crystal lattice of A. »The use of tie lines determines the composition of and –Fig 9-16 Pb-Sn System »Common solder alloys for binary eutectic »Solder (< 5% tin) used for sealing, 120C »Solder (20% tin) used for radiators »Solder (50% tin) used general purpose Temp, C Composition Fig 9-11 Solidus A+B 0 20 40 60 80 100 AB Liquid, L A + L B + L Temp, C Composition Fig 9-14 Eutectic Layered A+B 0 20 40 60 80 100 AB Liquid, L Crystallites of B in matrix L2 Crystallites of A in matrix L1
Copyright Joseph Greene 2002 All Rights Reserved 12 Eutectoid Diagram Transformation of eutectic liquid to a relatively fine-grained microstructure of two solid phases upon cooling can be described as special type of chemical reaction Liquid (eutectic) + –Notation corresponds to Fig 9-14 –Fig 9-17 –Fig 9-18 representative microstructures –Eutectoid reaction play important role in steel industry Fe-Fe3C system Fig 9-19 is basis for commercial steel Chapter 11. Irons and steels boundary is with 2% carbon, which is the carbon solubility of austenite Diagram represents the microstructure development Important areas are eutectic and eutectoid reactions Temp, C Composition Fig 9-17 Solidus + 0 20 40 60 80 100 AB Liquid, L + L + L + Eutectic + Composition Fig 9-18 Eutectoid micro structure fine of AB Liquid, L Eutectic Temps + +
Copyright Joseph Greene 2002 All Rights Reserved 13 Iron-Carbon Phase Diagram Iron and Carbon are two main elements in steels. –Ferrite- alpha iron. BCC and magnetic. Alpha/delta = pure iron Room temp dissolve only 0.008% C. Delta iron if T is between 2552F and 2802F Small amount of carbon dissolves interstitially (imperfection in the lattice) –Carbon steel of 0.77% carbon (eutectoid- lowest T a single phase can exist before becoming 2). All carbon dissolved into austenite. –Austenite- gamma iron. FCC and non-magnetic. –Steel must be taken into austenite region for all hardening and softening. When solution cools slowly steel separates into 2 distinct phases, ferrite and cementite. –Cementite- very hard and brittle compound, not alloy. –Iron is allotropic- can exist in more than one phase.
Copyright Joseph Greene 2002 All Rights Reserved 14 Eutectoid Diagram Fe-Fe 3 C diagram is not true equilibrium. –Fe-C system represents true equilibrium Fig 9-20 Graphite C is more stable precipitate that Fe 3 C, the rate of graphite precipitation is enormously slower than that of Fe 3 C. Result is that in common steel the Fe 3 C is metastable (stable at common T, P, and time) and follows Gibbs phase rule –Fe-C is more stable but less common than Fe 3 C because of slow kinetics (Chap 10) Extremely slow cooling rates can produce the results indicated on Fe-C diagram. (Fig 9-20) More practical method is to promote graphite precipitation is to add silicon (2 to 3%) stabilizes the graphite precipitation
Copyright Joseph Greene 2002 All Rights Reserved 15 Iron-Carbon Phase Diagram Iron is ferromagnetic- magnetism is dependent upon which crystalline structure is present due to Carbon content and temperature. Curie Temperature- temperature at which magnetism changes Ferrite holds between 0.006% Carbon at 392F and up to 0.04% at 1333F. Austenite holds 0.77% at 1333F and up to 1.7% at 2066F Pearlite is an eutectoid mixture of ferrite and cementite which form a lamellar structure. Hypoeutectoid -less carbon and Hypereutectoid- more carbon than eutectoid composition for the steel. Martensite- very hard and very brittle steel and forms when steel is rapidly cooled from the austenite state. Ferrite with highly saturated Carbon trapped in BC tetragonal structure.
Copyright Joseph Greene 2002 All Rights Reserved 16 Phase Diagram Peritectic Diagram –In some systems, components form stable compounds that may not form stable compounds that have a distinct melting point. Example, Fig 9-21 A and B form a stable solid compound AB, which does not melt at a single temperature as do A and B. A and B undergo congruent melting (liquid forms upon melting has the same composition as the solid from which it was formed. AB (50% A and 50% B) undergoes incongruent melting (liquid formed after melting has composition other than AB. AB L + B Peritectic comes from Greek “To melt nearby” Fig 9-21 and Fig 9-22 shows microstructures for peritectic Fig 9-23. Al 2 O 3 -SiO 2 is an example of peritectic diagram –Very important to ceramic industry –Others are refractory silica bricks (SiO 2 ) with 1% Al 2 O 3 »Need to keep Al 2 O 3 content as low as possible
Copyright Joseph Greene 2002 All Rights Reserved 17 Phase Diagram General Binary Diagrams –Intermediate compounds are formed in peritectic diagram. Chemical compound formed between two components in binary system Fig 9-24 –AB melts congruently –It is equivalent to adjacent binary eutectic diagrams (Fig 9-11) –A-AB binary does not exist for overall composition Fig 9-24b. –Nowhere in the development of microstructure for that composition will crystals of A be found in a liquid or will crystals of A and AB exist simultaneously. Fig 9-25 demonstrates this for complex binary system –Diagram with 4 intermediate compounds (A 2 B, AB, AB 2, and AB 4 ) and several individual binary diagrams. –For overall compositions only AB 2 – AB 4 binary is relevant Fig 9-26 –MgO-Al 2 O 3 is similar to 9-24 but with limited solid solubility. –Includes important intermediate compound (spinel- magnetic materials) –Figures 9-27 to 9-29 good examples of general binary diagrams »Age hardenable Al in area. »Complex diagram can be analyzed as simple binary eutectic in high Al region
Copyright Joseph Greene 2002 All Rights Reserved 18 Phase Diagram General Binary Diagrams –Fig 9-28 Al-Mg phase diagram Several Al alloys and Mg alloys can be described by phase diagram –Fig 9-29 Cu-Zn phase diagram Complex diagram that can be used for single phase region ( region) –Fig 9-30 CaO-ZrO 2 phase diagram Example of general diagram for a ceramic system. ZrO 2 is an important refractory material through the use of stabilizing additions, such as CaO. Pure ZrO 2 has a phase transformation at 1000C in which the crystal structure changes from monoclinic to tetragonal upon heating. –Transformation involves a substantial volume change that is structurally catastrophic to the brittle ceramic. –Cycling pure material through the transformation temperature will reduce it to a powder. –Addition of 10wt% CaO produces a solid solution-phase with a cubic crystal structure from room temperature to the melting point (2500C) –Stabilized zirconia is a practical, refractory, structural material
Copyright Joseph Greene 2002 All Rights Reserved 19 Lever Rule Previously, phase diagrams were used to determine present at equilibrium that corresponds to a microstructure. Tie line (Fig 9-6) gives the composition of each phase in the two-phase region. –Tie line can determine the amount of each phase in the 2-phase –Note: for single-phase region, microstructure is 100% single phase –For 2-phase systems the amount of each is found per mass balance Example, Fig 9-31(Fig 9-6 with values) –Tie line gives composition of 2 phases with point, L +SS region, and the composition of each phase and of overall composition of system. –Overall mass balance requires sum of two phases equal total system. »Step 1. Assume 100 g for system, then »Step 2. Mass balance on one of the components. »Step 3. Solve two equations with two unknowns
Copyright Joseph Greene 2002 All Rights Reserved 20 Lever Rule For 2-phase: the amount of each is found per mass balance –Example, Fig 9-31(Fig 9-6 with values) Tie line gives composition of 2 phases with point, L +SS region, and the composition of each phase and of overall composition of system. Overall mass balance requires sum of two phases equal total system. –Step 1. Assume 100 g for system, then Equation 1 is »m L + m SS = 100g –Step 2. Mass balance on one of the components, then Equation 2 is »Amount of B in liquid (L) phase plus that in Solid Solution (SS) must equal the total amount of B in overall composition. »Fig 9-31, 0.3 m L + 0.8 m SS = 0.5 (100g) = 50g –Step 3. Step 3. Solve two equations (1 and 2) with 2 unknowns m L,m SS »Write equation 1 into m L = 100g - m SS »Substitute 100g - m SS for m L in Equation 2 »0.3(100g – m SS )+ 0.8m SS = 50g »Solve for 0.5 m SS = 20g or m SS = 40g »Then from Equation 1; m L + 40g = 100g; m L = 60g
Copyright Joseph Greene 2002 All Rights Reserved 21 Lever Rule Lever Rule method –Lever rule Material balance method is convenient, but a streamlined method is: Mass balance in general terms. –x m + x m = x (m + m ) –x x are the compositions of the two phases and x is the overall composition. Expression can be rearranged as –These equations are the lever rule »Fig 9-32. Mechanical analogy is to a lever balance on a fulcrum »Mass of each phase is suspended from the end of the lever corresponding to its composition »Relative amount of phase is directly proportional to the length of the opposite lever arm (=x – x) »Sample Problem 9.3
Copyright Joseph Greene 2002 All Rights Reserved 22 Microstructural Development Development of various binary systems –Assume: microstructure is developed during solidification –Only consider slow cooling- equilibrium is achieved at all points –Simple binary systems Complete solubility in both liquid and solid phases Fig 9-33. Slow solidification of 50% A 50% B treated earlier Microstructures corresponds with relative position of overall system composition along the line. –High Temp, overall composition is near L-solid boundary and microstructure is liquid. –Low temperature, microstructure is mostly solid. Composition of binary at Eutectic is aided by lever rule –Fig 9-34. Only differences from T1 microstructure are the phase compositions and the relative amount of b will be proportional to
Copyright Joseph Greene 2002 All Rights Reserved 23 Microstructural Development Development of various binary systems –Microstuctural development, noneutectic composition is complex Fig 9-35 for hypereutectic composition (composition greater than eutectic) –Gradual growth of crystals above eutectic Temp is a similar to Fig 9-33, except that the crystals stop growing at eutectic temp with only 67% of the microstructure solidified. Final solidification occurs when the remaining liquid transforms to eutectic microstructure upon cooling. »33% of microstructure undergoes eutectic reaction in Fig 9-34 »Lever rule calculates that microstructure is 17% and 83% (In two forms- large grains during slow cooling (proeutectic) and finer lamellar eutectic structure . Fig 9-36 similar situation for hypoeutectic (Less than eutectic composition) –Analogous to hypereutectic composition »Development of large grains of proeutectic along with the eutectic microstrucre of and Fig 9-37 Two other types of microstructural development –Overall composition of 10% , similar to that of complete solid solution »Leads to single phase solid solution that remains stable upon cooling to low Temp –Overall 20% solution leads to precipitation of small amounts of phase along grain boundaries.
Copyright Joseph Greene 2002 All Rights Reserved 24 Microstructural Development Fig 9-38. Cooling path of white cast iron –Microstructure produces eutectoid reaction to produce pearlite –Hypereutectoid composition –Proeutectoid composition Fig 9-39 Microstructural development for eutectoid steel (C < 0.77% Fig 9-40. Fe-C diagram for gray cast iron
Copyright Joseph Greene 2002 All Rights Reserved 25 Carbon Content in Steels Carbon is the most important alloying element in steel. Most steels contain less than 1% carbon. Plain carbon steel- carbon is the only significant alloying element Mild steel, or low carbon steel, are produced in the greatest quantity because it is cheap, soft, ductile, and readily welded. Caution: it can not be heat-treated Mild steels are used for car bodies, appliances, bridges, tanks, and pipe.
Copyright Joseph Greene 2002 All Rights Reserved 26 Carbon Content Cold Working in Steels Medium carbon steel - used for reinforcing bars in concrete, farm implements, tool gears and shafts, as well as uses in the automobile and aircraft industries. High carbon steels - used for knives, files, machine tooling, hammers, chisels, axes, etc. A small increase in carbon has significant impact on properties of the steel. As Carbon increases the steel: –becomes more expensive to produce and less ductile, i.e., more brittle –becomes harder and less machinable and harder to weld –has higher tensile strength and a lower melting point Cold working is used to enhance the properties of steel –Reducing thickness by 4% raises the tensile strength by 50% –Cold working is plastic deformation at room temperature. –Cold working produces dislocations in the metal’s structure which block dislocations as they slide along the slip planes
Copyright Joseph Greene 2002 All Rights Reserved 27 Other Elements in Steels Alloying elements are added to nullify undesirable elements –Carbon –Manganese increases strength, malleability, hardenability, and hardness Sulfur reacts with the Mn which reduces the hot short effect of the iron sulfide accumulating at the grain boundaries and reducing strength at Temp –Aluminum- reacts with Oxygen versus iron (no sparks). Killed steel promotes smaller grain size which adds toughness –Silicon- reduces Oxygen negative effects –Boron- increases the hardenability of steel (only with Al added) –Copper- increases corrosion resistance –Chromium- increases corrosion resistance and hardenability –Nickel, Niobium, titanium, tungsten carbide, vanadium increase toughness and strength and impact resistance
Copyright Joseph Greene 2002 All Rights Reserved 28 Nomenclature in Steels SAE and AISI developed method of cataloging steel based on –carbon content- % carbon with implied decimal –alloying elements –AISI 8620 steel is the same as SAE 8620 steel Steels are usually 4 digit designations –1018 steel = 10 is plain carbon steel; 18 represents 0.18% carbon –4030 steel = 40 is molybdenum steel of.15% to 0.30% Molybdenum and 0.30% carbon –2 - - - = nickel steel with % nickel, 22-- is nickel with 2% nickel –10100 = five digits indicated 1% carbon more –B in the middle of the number, 81B40 indicates min of 0.0005% boron Various common steels –1010: Steel tuning; 1040: Connecting rods for automobiles –4140: Sockets and socket wrenches; 52100: Ball and roller bearings –8620: Shafts, gears, and machinery parts.
Copyright Joseph Greene 2002 All Rights Reserved 29 Cast Iron Other ferrous metals include –cast iron (gray-3.5% carbon and >1% silicone and white- 2.5 - 3.5% carbon and 0.5 - 1.5% silicon. ) –ductile cast iron, malleable cast iron, wrought iron Steel with >2% iron is cast iron because of the lack of ductility. Carbon in form of graphite (gray) or iron carbide (white) Gray cast iron has no ductility and will crack if heated or cooled too quickly. –Gray cast iron has good compression strength, machinability, vibration damping characteristics and used for furnace doors, machine bases, and crackshafts. White cast iron has good wear resistance and is used in rolling and crunching equipment Ductile cast iron contains 4% Carbon and 2.5% Silicon Ductile iron is used for engine blocks, machine parts, etc. Maleable cast irons are heat treated versions of white cast iron. –Cast iron with 2 to 3% Carbon is heated to 1750F, where iron carbide or cementite is allowed to form spherulites. Similar to ductile cast iron –Pearlitic malleable iron- heated to 1770F and quenched cooled –Ferritic malleable iron- heated to 1770F and air cooled
Copyright Joseph Greene 2002 All Rights Reserved 30 Stainless Steel Definition and Applications –Alloys that posses unusual resistance to attack by corrosive media –Applications include aircraft, railway cars, trucks, trailers,... AISI developed a 3digit numbering system for stainless steels –200 series: Austenitic- Iron-Cr-Ni-Mn Hardenable only by cold working and nonmagnetic –300 series: Austenitic- Iron-Cr-Ni Hardenable only by cold working and nonmagnetic General purpose alloy is type 304 (S30400) –400 series: Ferritic- Iron-Cr alloy are not hardenable by heat treatment or cold working –Type 430 (S43000) is a general purpose alloy Martensitic- Iron-Cr alloys are hardenable by heat treatment and magnetic –Type 410 (S41000) is a general purpose alloy
Copyright Joseph Greene 2002 All Rights Reserved 31 Stainless Steel Corrosion of steels can be slowed with addition of Cr and Ni. Stainless steels have chromium (up to 12%) and Ni (optional) –ferritic stainless: 12% to 25% Cr and 0.1% to 0.35% Carbon ferritic up to melting temp and thus can not form the hard martensitic steel. can be strengthened by work hardening very formable makes it good for jewelry, decorations, utensils, trim –austenitic stainless: 16% to 26% Cr, 6% to 23% Ni, <0.15% Carbon nonmagnetic and low strength % to 25% Cr and 0.1% to 0.35% Carbon machinable and weldable, but not heat-treatable used for chemical processing equipment, food utensils, architectural items –martensitic stainless: 6% to 18% Cr, up to 2% Ni, and 0.1% to 1.5% C hardened by rapid cooling (quenching) from austenitic range. Corrosion resistance, low machinability/weldability used for knives, cutlery. –Marging (high strength) steels: 18% to 25% Ni, 7% Co, with others heated and air cooled cycle with cold rolled Machinable used for large structures, e.g., buildings, bridges, aircraft
Copyright Joseph Greene 2002 All Rights Reserved 32 Corrosion Ferrous metals rust because the iron reacts with oxygen to form iron oxide or rust. Process is corrosion Corrosion occurs as well when metal is in contact with water and metal ions dissolved in water. Galvanic corrosion: electrochemical process which erodes the anode. Metals in galvanic series: the further apart the worse the corrosion –Magnesium- most positive or anodic. Gives up electrons easily and corrodes –Aluminum –Zinc –Iron –Steel –Cast Iron –Lead Brass –Copper –Bronze –Nickel –Stainless steel –Silver –Graphite
Copyright Joseph Greene 2002 All Rights Reserved 33 Wrought Aluminum Numbering System Wrought Numbering System –Aluminum Association developed system for cast and wrought Al –Wrought aluminum- 4 digit system, e.g. 2011 first digit represents alloying elements in the alloy second digit represents alloy modifications or degree of control of impurities third digit represents arbitrary numbers that indicate a specific alloy or indicate the purity of the alloy over 90% fourth digit represents same as third digit
Copyright Joseph Greene 2002 All Rights Reserved 34 Wrought Aluminum Numbering System Common aluminum alloys –Silicon alloys used for castings –Copper alloys used for machining –Magnesium alloys used for welding –Pure aluminum used for forming –Magnesium and silicon alloys used for extrusion –Copper alloys used for strength Examples –2011 with 5% to 6% copper is a free machining alloy –2024 contains between 3.8% and 4.9% copper with 1.5% magnesium. This alloy is heat treatable aluminum alloy that is commonly used for aircraft parts. –3003 has 1% to 1.5% manganese which provides additional strength –4043 contains 4.5% to 6% silicon and is used in welding wire –5154 contains 3.1% to 3.9% magnesium and is weldable and available in sheets, plates, and many structural shapes. –6063 contains approximately 0.5% magnesium and silicon and is used in windows, doors, and trim
Copyright Joseph Greene 2002 All Rights Reserved 35 Casting Aluminum Numbering System Casting Numbering System –Cast aluminum- 3 digit system that is not generally standardized –Aluminum Association developed system for cast silicon casting alloys up to 99 silicon copper from 100 to 199 magnesium from 200 to 299 silicon manganese from 300 to 399 –Applications Good conductor for electrical and electronics applications Light weight good for structural applications that require medium strength and light weight. High reflectivity for infrared and visible radiation make it desirable for headlights, light fixtures, and insulations Flake form is used for pigment Cast Al engine blocks and pistons