1. D AY 18: F ERROUS A LLOYS, A LUMINUM AND M ORE Cast Iron Aluminum Titanium Copper Goals for tomorrow: Whatever we miss today + Zn, Mg, other metals. Review. Material selection discussion.

2. T YPES OF C AST I RON 1. Grey 2. White 3. Malleable 4. Ductile 5. Compact Graphite The form in which the carbon appears in the iron matrix is very important, and determines the use and properties.

3. C AST I RON steelCast iron Notes: 1.Significance of Eutectic (ledeburite is the name of the eutectic mix of  and Fe 3 C.) 2.Silicon is often an important 3 rd component

4. 4 F E -C T RUE E QUILIBRIUM D IAGRAM Graphite formation promoted by Si > 1 wt% slow cooling Adapted from Fig. 11.2,Callister 7e. (Fig. 11.2 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.- in-Chief), ASM International, Materials Park, OH, 1990.) 1600 1400 1200 1000 800 600 400 0 1234 90 L  +L +L  + Graphite Liquid + Graphite (Fe) C o, wt% C 0.65 740°C T(°C)  + Graphite 100 1153°C  Austenite 4.2 wt% C 

5. G RAY C AST I RON By far the cheapest and most common. Presence of Silicon + slow cooling rate causes graphite to form instead of cementite, Fe 3 C. The graphite is in flake form. See micrograph. What we have: 1.Graphite flakes. Look like cornflakes 2.Pearlite matrix

6. http://www.nikonsmallworld.com/gallery/search/description s/cast+iron/1

7. M ORE ON G RAY I RON The presence of the sharp-cornered flakes creates stress risers which make gray iron very brittle. However, there are good results as well 1. Low shrinkage – very castable! 2. Excellent machinability 3. Excellent damping This material is very useful in situations where no tensile strength is required.

8. P ROPERTIES AND U SES About 3.5% C, 2% Si. UTS about 40 Ksi Ductility and yield strength not given, because it’s really brittle. How do the properties of cast iron make it such an ideal material for this application?

9. W HITE C AST I RON We cool fast enough and with less Silicon so that graphite flakes do not form. The result is a material with lots of cementite, Fe 3 C. Extremely hard and brittle. Result: 1. Not easily machined 2. Often you have white iron on the surface and grey iron in the interior of the casting. This is a chilled casting and is desirable. 3. Uses: where very hard, wear resistant surface

10. W HITE C AST I RON Massive cementite – white + Pearlite

11. D UCTILE C AST I RON Nodular iron or Spherical. We take away as much S as possible and innoculate with a Mg alloy. This causes graphite to form in spherical clumps instead of flakes. This has a tremendous effect on mechanical properties. Yield: 276 MPA, 40 Ksi Ultimate: 414 MPA, 60 Ksi Ductile: 18% EL Please note that this stuff is castable. This is very important – has steel like properties in a casting!

12. N ODULAR / SPHERICAL C AST IRON

13. U SES OF D UCTILE I RON Complex geometries + need for tensile strength. Valve body Shafts which take tension Pump housings Gears Engine blocks Ductile Iron can be really strengthened by austempering. That way the spherical graphite lives in a bainite matrix. http://www.ductile.org/didata/section4/4intro.htm

14. M ALLEABLE I RON - B LACKHEART This has similar properties to the previous iron. But to get it, we start with white cast iron and reheat it for an extended period of time (hours). The cementite decomposes into graphite in clumps. (Recall that grey iron has sharp flakes). Consequently, we have ductility. This approach is not used as frequently now as it was in the past. White cast iron is hard to get in thick sections, therefore the same is true for malleable iron.

15. C OMPACT G RAPHITE IRON A relatively new approach – get somewhere in between gray and ductile as far as properties go. I’ll let you do the research. This one will not be on the next quiz.

16. 16 T YPES OF C AST I RON Gray iron graphite flakes weak & brittle under tension stronger under compression excellent vibrational dampening wear resistant Ductile iron add Mg or Ce graphite in nodules not flakes matrix often pearlite - better ductility Adapted from Fig. 11.3(a) & (b), Callister 7e.

17. 17 T YPES OF C AST I RON White iron <1wt% Si so harder but brittle more cementite Malleable iron heat treat at 800-900ºC graphite in rosettes more ductile Adapted from Fig. 11.3(c) & (d), Callister 7e.

18. 18 P RODUCTION OF C AST I RON Adapted from Fig.11.5, Callister 7e.

19. A LUMINUM F ACTS Light metal: 2.7 g/cm 3 vs 7.9 g/cm 3 for steel. Can be very strong: UTS up to 80 ksi. Competitive with steel at a fraction of the weight. Very corrosion resistant. Forms a tenacious passive oxide layer on the surface. Extremely plentiful in earth’s crust, yet very hard to extract from its ore. Hall-Heroult process requires extensive electricity for electrolysis. Very recyclable. Not good at high temperatures.

20. P RECIPITATION H ARDENING IN A LUMINUM Super-saturated Ageing- get coherent precips and get max strength Over-aging. Precipitates no longer coherent.

21. A GEING C URVES UTS Ductility A precipitation hardened Al alloy will be sensitive to exposure to high temperatures over extended time, will be difficult to weld and will be more prone to corrode.

22. T YPES OF A LUMINUM A LLOYS Wrought, no heat treatment, but may be strengthed with cold work. Wrought, heat-treatable and cold worked Cast, Heat treatable. Aluminum is very castable. Lots of die casting is done. Due to low mp, about 660C. Fact: Al has a modulus of elasticity about 1/3 that of steel. Al structures will be far less stiff than steel for the same geometry.

23. W ROUGHT A LLOY 1100 series alloy. Basically commercially pure Al. According to Matweb Yield: 103 Mpa, 15 Ksi. UTS: 110 Mpa, 16 Ksi. Ductility: 25%EL. (in 50mm) Widely used in cheap aluminum products. Not for strength.

24. W ROUGHT – H EAT T REATABLE The strongest Al is 7075. Alloys are Zn, Mg, and a little Cu. This alloy depends of precipitation hardening. Yield: 462 Mpa, 67 Ksi. (Competitive with steel.) UTS: 524 Mpa, 76 Ksi. Ductility: 11%EL. (in 50mm) Widely used in aerospace applications where a superior strength to weight ratio is needed. Aircraft structural parts.

25. H OW IS A LUMINUM USED IN CARS http://www.autoaluminum.org/main/aluminum-processes-and- materials/aluminum-processes-and-materials http://www.autoaluminum.org/main/news- releases/automotive-aluminum-use-reaches-all-time-high-in

26. T ITANIUM Light metal: 4.5 g/cm 3 vs 7.9 g/cm 3 for steel. Can be very strong: UTS up to 200 ksi. Competitive with steel at a fraction of the weight, but you have to pay the price. Very corrosion resistant. Forms a tenacious passive oxide layer on the surface. Very reactive at high temperatures. Has to be produced in special process. Expensive.

27. M ORE ON T ITANIUM Wikipedia says up to 77 tons will be used in each A-380. Extremely corrosion resistant. Now also seeing commodity use. Be careful, it might be a fake. I.e. golf clubs! Komsomolets: Soviet era attack sub had Titanium hull. OR DID IT?

28. C OPPER Heavier than Fe, about 9.0 gm/cc. One of the earliest metals. MP 1100C. In unalloyed form, not very strong, but extremely ductile. Yield: 5 Ksi, UTS: 30.5 Ksi, %EL = 60%. Electical conductivity is key to its use in all kinds of electrical equipment and conductors. Copper is also the base metal for two families of alloys: 1. Brasses (with Zn) 2. Bronzes (with Sn and other metals)

29. PropertyIndustry/Type of Application AestheticsArchitecture, sculpture, jewelry, clocks, cutlery. Bactericide Door hardware, marine internal combustion engines, crop treatments. Corrosion resistance Plumbing tubes and fittings, roofing, general and marine engineering, shipbuilding; chemical engineering, industrial processes including pickling, etching and distilling; domestic plumbing, architecture, desalination, textiles, papermaking. Electrical conductivity Electrical power generation, transmission and distribution, communications, resistance welding, electronics. Low temperature properties Cryogenics, liquid gas handling, superconductors. Mechanical strength/ductility General engineering, marine engineering, defense, aerospace. Non-magnetic Instrumentation, geological survey equipment, minesweepers, offshore drilling. Non-sparkingMining and other safety tools, oxygen distribution. Elasticity Electrical springs and contacts, safety pins, instrument bellows, electronic packaging. Thermal conductivity Heat exchangers and air-conditioning/refrigeration equipment, automotive radiators, internal combustion engines, mining. Copper

31. B RASS Very attractive metal. Excellent corrosion resistance. Excellent ductility Cartridge brass: 30%Zn Yield 63 Ksi UTS 76 Ksi Ductility %EL = 8% (After cold working.)

32. B RONZE Numerous alloys based on Sn, Ni, Aluminum, etc. Tin bronze: UTS is 45 ksi, Yield is 22 ksi, %EL = 25%. (Cast alloy) Used for bearings, bushings, fittings and gears.