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Lecture15%20with%20slides - VK250 Lecture 15 LIGHT ALLOYS...

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VK250 Lecture 1 5 1 L IGHT A LLOYS ρ kg/m 3 E GPa σ Y (MPa) E / ρ MPa/(kgm -3 ) σ Y / ρ MPa/(kgm -3 ) Al alloys 2700 71 25-600 26 0.0093-0.22 Mg alloys 1740 45 70-270 25 0.040-0.16 Ti alloys 4500 120 170-1280 27 0.038-0.28 Steels 7900 210 220-1600 27 0.028-0.20 For stiff-light beams maximize E 1/2 / ρ For strong-light beams maximize σ Y 2/3 / ρ This is where light alloys come into their own over steels E 1/2 / ρ (Pa) 1/2 /(kgm -3 ) σ Y 2/3 / ρ (Pa) 2/3 /(kgm -3 ) Al alloys 99 32-260 Mg alloys 120 98-240 Ti alloys 77 68-260 Steels 58 46-173 Light alloys are also corrosion resistant Designation of aluminum alloy of form 7075-T651 Aluminum alloys Major addition Minor additions Yield strength (MPa) 1xxx none none 25-125 2xxx 4% Cu Mg, Mn, Si 28-165 3xxx Mn Mg, Cu 4xxx Si none 5xxx Mg Mn, Cr 200-500 6xxx Mg, Si Cu, Mn 40-300 7xxx Zn Mg, Cu, Cr 350-600 Cast Al 11% Si 65-350 Specific examples: 2014 - 4.4% Cu, 0.5%Mg, 0.8% Mn, 0.8% Si 2024 - 4.4%Cu, 1,5% Mg, 0.6% Mn, 2219 - 6.3% Cu, 0.3%Mn
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VK250 Lecture 15 2 Final code indicates processing (may be annealing, cold-work, or thermal treatment) HXX - indicates cold work TXX - indicates type of heat treatment Composition and processing dictate yield strength of alloy - must know both Strength of light alloys may come from Solid-solution hardening Age (precipitation) hardening Work hardening Solid-solution hardening 3xxx, 4xxx and 5xxx series are hardened this way Example Al - 5.5wt% Solution heat treatment Hold at 450 ° C to form a single phase (solid solution of Mg in Al) Moderately quick cooling to room temperature (avoid α saturated α + Mg 5 Al 8 ) Result is a super-saturated solid solution Equilibrium would be 1.8 wt% Mg at room temperature, Super-saturated solution has 5.5 wt% Mg
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VK250 Lecture 15 3 Remember: Yield strength increases with concentration - increasing c above equilibrium increased σ Y Alloy wt % Mg σ Y (MPa) annealed) 5005 0.8 40 5050 1.5 55 5052 2.5 90 supersaturated 5454 2.7 120 supersaturated 5083 4.5 145 supersaturated 5456 5.1 160 supersaturated Strength of Ti-6Al-4V is dominated by solution hardening (Ti dissolves 7 wt% Al, complete solubility for V) Mg alloys solution strengthened with Li, Al, Ag & Zn (2-5 wt% dissolve in Mg) Not heat-treatable alloys - strength unmodified by subsequent heat treatment Additional strengthening can be obtained by work-hardened (as with 1xxx Al) σ Y increases from 140 MPa to 370 MPa for 5456 alloy 35 MPa to 145 MPa for 1100 alloy Advantage of solution-hardened alloys: can be welded without loss of strength.
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