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Physical Metallurgy

Physical Metallurgy. 23nd Lecture. MS&E 410. D. Ast. dast. @. ccmr. cornell. edu. 255 4140. 1. Aluminum and Aluminum Alloys. History Unlike steel, bronze. Al only “recently” used

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Physical Metallurgy

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  1. Physical Metallurgy 23nd Lecture MS&E 410 D. Ast dast @ ccmr . cornell . edu 255 4140

  2. 1. Aluminum and Aluminum Alloys

  3. History • Unlike steel, bronze. Al only “recently” used • First shown at the Exposition Universelle in Paris in 1855 as "silver from clay” by Deville • Sainte-Claire Deville's sponsored by Napoleon III • Hopes for military use faded (well until the metal airplane!) • Used for jewelry (by 1860 price had fallen to that of silver) • 1886. Charles Martin Hall (1863-1914), US and Paul T. Heoult (1863-1914), France, independently discover electrolytic method for making aluminum. • Price falls from $ 12/lb to .36/lb (about • Teakettles, furniture (cast Al), building facades... Hall Heoult

  4. Production Hall, a chemist, graduated in 1885 from Oberlin, set out to find a non-aqueous solvent in his garage and found cryolite in Feb 23. 1886. Died,very rich , in Daytona Beach, 1914 at age 51.

  5. The Hall-Heoult Process • Find as pure as possible bauxite (aluminum oxide) • Treat with alkali, to remove the impurities, in particular Fe. • Dissolve alumina in molten cryolite - this lowers the melting • Cathode (negative pole of DC power, graphite bed) • Anode (positive pole of DC power, graphite pods) • Aluminum is reduced from Al+++ to Al , oxygen is oxidized from O-- to O.

  6. World wide tonnage Bauxite Producers Largest Companies

  7. Al production, by country. Note: In 1999, US largest producer. In 2003, China largest producer.

  8. Properties • Light weight => 35% of Fe • Hence, high specific stiffness and strength per weight • Good thermal and electrical conductor • High reflectivity in UV (unlike Ag) and visible • Good acid corrosion resistance • Easy to form to tight tolerances at low cost (injection molding) • Low resistance against base corrosion • Low resistance against halides (salt !) • Low melting point :-( (Limits use in IC • Low creep resistance :-( (Enables electro-migration)

  9. Al is the second best conductor after Cu. Al has excellent adhesion to Si and SiO2. Al remains a popular conductor for IC’s Heat of formation Al(2)O(3) -1675.7 KJ/mol SiO(2) -910.86 Thus, Al will dissolve the native oxide on Si

  10. Pure Al is used in • Electrical and electronics (overhead power lines are either Al or Al reinforced with a steel or high tensile strength Al-alloy core) • Cook ware • Aluminum foil Al wires Steel core Power line

  11. Pure Al wasused in household wiring but discontinued • Al creeps under stress ( Tservice Tm/2 ) • Reduces contact pressure at switches, outlets over time • Sparking develops • Fire • Efforts to sell precut length Al wires with Cu terminations (Cu pig tails) have not succeeded commercially.

  12. A classic example of a delayed failure mode (creep by point defects) that escaped testing. Now a major liability

  13. Aluminum alloy products • Bars, rods of all profiles • Sheets (cars, building facades..) • Extruded parts • Cast parts • Heat exchangers (e.g. car radiators) • Aircraft's.. • ………………..Too numerous to mention all

  14. Nomenclature • 1000 pure (99% +). Foils, cookware, conductors. • 2000 Al + Cu. “Duraluminum” Correct heat treatment to generate coherent Cu precips (Gunieir-Preston Zones). Strong but stress corrosion prone. Being replaced by 7000 series.. • 3000 Al+Mn • 4000 Al+Si silicon. “Silumin” Popular with Porsche for Cylinders • 5000 Al+Mg, solution strengthening when work hardened can reach construction steel level. Beloved by the US and UK navy but a series of fires prompted them abandon this alloy for superstructures and return to steel • 6000 Mg+Si , easy to machine, and can be precipitation hardened • 7000 Al+Zn,strongest of Al alloys, precip hardened • 8000 series are a miscellaneous category

  15. Composition Marine Alloy Marine

  16. 5083 and 5086 not (!) work hardened 17KSI yield strength work hardened 30 KSI The Bradely IFV is build with 5086

  17. A closer look : 7052 Type Cu + Mg + Zn precipitate hardening; some Cr to increase resistance to stress corrosion cracking. From AlCOA

  18. T => heat treatment. Note universal trade of between tensile strength and ductility

  19. Longitudinal Transverse

  20. To be safe under cyclic loading> 107stress needs to be < 5 KSI This is the problem of the aircraft industry/designer

  21. Modern aircraft are designed using fracture mechanics using crack growth data like the one on the left

  22. This short haul plane (Aloha) suffered a metal fatigue failure in flight One solution is to sell an aircraft after >104 Cycles to a far away airline in a country with no safety standards/enforcement

  23. An aircraft flying 10 hrs a day accumulates 3650 hours per year. The average age of Hawaii Airline Aloha is 17.9 years, American 14.7, North- west 18.5 US Air 12.2

  24. G-P Zones, revisited Single or double planes of Cu, parallel to (100) planes of Al

  25. Salient points G-P Zones • Formed during aging (naturally, accelerated at ~ 100C) • Want coherent precipitates • Overaging leads to incoherent precipitates • Previous work hardening strongly influence precipitation (we discussed nucleation of G-P zones at dislocations) • Heat treatment is prescribed and most be followed

  26. The temper designation appears as a hyphenated suffix to the basic alloy number. • Example 7075-T73 where -T73 is temper designation. • Four basic temper designations are used • -F: as fabricated; • -0: annealed; • -H: strain hardened • -T: • -W, quenched condition between solution heat treatment and artificial or room temperature aging.

  27. Example -T31: Solution heat treated and then cold worked by flattening or stretching. Applies to 2219 and 2024 sheet and plate per MIL-A-8920. Also applies to rivets driven cold immediately after solution heat treatment or cold storage. 2024 rivets are an example. -T351: Solution heat treatment and stress relieved by stretching. This is equivalent to -T4 condition. It applies to 2024 plate and rolled bar and 2219 plate per MIL-A-8920. -T3511: Solution heat treated and stress relieved by stretching with minor stretching allowed. This is equivalent to -T4 condition and applies to 2024 extrusions. Etc…… there a pages !!!

  28. Ni Alloys We discussed those as a subset when we discussed stainless steels. Ni increases the g field More narrowly Monel 400 Hastelloy Inconel 600 Incolloy 825

  29. Monel: Ni (dominant) + Cu High yield strength (35 KSI), ductile (UTS 80 KSI), very corrosion resistant. Beautiful color. Marine, Food processing, Chemical Industry. Expensive

  30. Hastelloy C-276 Mostly Ni and Cr. Not a stainless Steel, which is mostly Fe. Excellent resistance to the sulfur compounds and chloride ions encountered in most powerplant scrubbers.

  31. Incoloy Nearly equal Fe and Ni. About 20% for oxidation resitance Excellent oxidation resistance at high temperatures

  32. Inconel 716 Mostly Ni and Cr. Amazing Material Gas turbines, rocket motors.

  33. Titanium and it alloys • Ti - named after Titans by Martin HeinrichKlathrop in 1795 • Production by the Kroll process, reducing TiCl4 with Mg (Carbon can not reduce Tio2 ; forms TiC) • Production of metal no data (perhaps of strategic interest ?), 95% of Ti mined goes for paint, top producer Australia

  34. ASTM Classification

  35. Main Classification • Alpha alloys (hexagonal), most ductile not heat treatable • Aluminium, gallium, germanium, carbon, oxygen and nitrogen are alpha stabilizers • Beta alloys (bcc), heat treatable, more brittle • Molybdenum, vanadium, tantalum, niobium, manganese, iron, chromium, cobalt, nickel, copper and silicon are beta stabilizers • Alpha-Beta dual, strongest (Ti-6Al-4V) • All Ti contains oxygen the presence of which increases the yield stress and decreases the toughness

  36. A closer look Ti-6Al-4V (most widely used Ti alloy, precipitation hardens via V) Oxygen is specified

  37. Density of Fe is 7.65 gr/cm3

  38. Properties are adjustable by heat treatment

  39. The END

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