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Chapter 11

Chapter 11. Applications and Processing of Metals and Alloys. Classification of Metal Alloys. Fabrication of Metals. Forming Techniques. Forging. Rolling. Wire drawing. Extrusion. Sheet Rolling. Multi-stand rolling mill. Extrusion. Chamber. product. Ram. Indirect Extrusion.

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Chapter 11

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  1. Chapter 11 Applications and Processing of Metals and Alloys

  2. Classification of Metal Alloys

  3. Fabrication of Metals

  4. Forming Techniques Forging Rolling Wire drawing Extrusion

  5. Sheet Rolling Multi-stand rolling mill

  6. Extrusion Chamber product Ram Indirect Extrusion Direct Extrusion Chamber Ram product

  7. Casting of metals • Molten metal is poured into a mold and allowed to solidify • Sand • A disposable mold is made by packing special granular materials and adhesives (“sand”) around a pattern. Liquid metal is poured into the cavity left behind when the pattern is removed • Die or permanent mold • A metallic mold which is reused • Investment or lost wax process • A mold cavity is formed by coating a “wax” pattern with ceramic materials. When liquid metal is poured into the mold, the wax melts away as the metal fills the cavity • Continuous casting

  8. Casting

  9. Continuous Casting

  10. Welding

  11. Annealing of Steel • Full anneal: Results in a very soft material • Heat to 50ºC above g solvus line (A3) and furnace cool (hypoeutectoid) • Heat to 50ºC above eutectoid temperature and furnace cool (hypereutectoid • Normalize: Results in a material harder than full anneal, but less expensive • Heat to 55ºC above g solvus line and air cool • Spheroidize: Converts plate like Fe3C to spherical particles • Heat to 40ºC below eutectoid temperature, hold for a long period of time and air cool A3 and Acm – Upper Critical Temperature A1 – Lower Critical Temperature

  12. Hardness and Hardenability • Hardness is a measure of the resistance of a material to indentation or abrasion • Hardenability is a measure of how easily a material can be hardened • Jominy End Quench Test • A test sample of standard dimensions is heated to above the eutectoid temperature • The sample is quickly transferred to the test fixture and the water jet is turned on • After the sample has cooled, the hardness is measured at different distances from the quenched end

  13. Jominy End Quench Test • Cooling rate decreases with increasing distance from the quenched end • The resultant microstructure along the length can vary from all martensite to all pearlite, depending on TTT diagram and the critical cooling rate for the particular steel • Hardness will therefore decrease as distance from the quenched end is increased

  14. Hardness and Hardenability Effect of carbon content on hardenability Hardness and hardenability increase with carbon content Effect of alloying on hardenability Last two digits in alloy designation indicate carbon content

  15. Effect of section size on hardness after quenching Quenching of shafts

  16. Precipitation Hardening or Age Hardening • Plastic deformation in metals is due to the movement of dislocations • Any hindrance to the movement of dislocations results in an increase in strength • A process of distributing second phase precipitates in a matrix in a controlled fashion to control hardness and strength • Typically used in alloys which show a sharp decrease in solubility as temperature is decreased

  17. Precipitation Hardening or Age Hardening • For an alloy of composition C0, at a temperature T0, the phase diagram shows a single phase • All B atoms are dissolved in the a phase • If the alloy is quenched to a low temperature T1, B is retained in solution • When reheated to T2, the phase diagram indicates a+b • B atoms will precipitate out as the b phase

  18. Precipitation Hardening or Age Hardening • The size and distribution of the b phase particles can be controlled by changing time and temperature • The second phase (b) particles impede dislocation motion and harden the alloy

  19. Precipitation Hardening or Age Hardening • Used extensively in Aluminum alloys • Example: Al-Cu system • Matrix phase is a (Al+ a small amount of Cu) • The equilibrium second phase phase is  (CuAl2 )

  20. Precipitation Hardening or Age Hardening • The  phase does not form right away • Instead several intermediate phases (GP zones, ’’ and ’) form first • With time the small precipitates grow in size and decrease in number to eventually become particles of  • Peak hardness is attained just as the ’’ phase converts to ’ phase

  21. Precipitation Hardening or Age Hardening • Aluminum alloy 2014 • Hardness and ductility depend upon precipitation treatment (aging) temperature and time

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