Precipitation Hardening (Summary)
• Particles impede dislocations. 700 • Ex: Al-Cu system T(°C) • Procedure: 600
--Pt A: solution heat treat (get solid solution) --Pt B: quench to room temp. --Pt C: reheat to nucleate small q crystals within crystals.
500 400
A
+L
L
q+L
CuAl2
C
20
+q
30 40 50
q
• Other precipitation systems:
• Cu-Be • Cu-Sn • Mg-Al
Adapted from Fig. 11.22, Callister 7e.
300 (Al) 0 B 10
composition range needed for precipitation hardening
wt% Cu
Temp. Pt A (sol’n heat treat)
Adapted from Fig. 11.24, Callister 7e. (Fig. 11.24 adapted from J.L. Murray, International Metals Review 30, p.5, 1985.)
Pt C (precipitate q)
Time
Pt B
Fig. 11.24. The aluminum-rich side of the aluminum-copper (Al-Cu) phase diagram
700
L α+L
T, oC
Temperature, oC
600
α
500
400
α+θ
Time
300 0 (Al) 10 Composition, wt.% Cu 20
Fig. 11.26. A transmission electron micrograph showing the microstructure of a 7150-T651 aluminum alloy that has been precipitation hardened.
Fig. 11.27a. The strength characteristics of a precipitation-hardened 2014 aluminum alloy
Fig. 11.27b. The elongation characteristics of a precipitation-hardened 2014 aluminum alloy
Precipitate Effect on TS, %EL (Summary) • 2014 Al Alloy: • TS peaks with precipitation time. • Increasing T accelerates process.
tensile strength (MPa)
• %EL reaches minimum with precipitation time.
400 300 200 100
%EL (2 in sample)
30 20 149°C
149°C
204°C 1min 1h 1day 1mo 1yr precipitation heat treat time
10 0
204°C
1min 1h 1day 1mo 1yr precipitation heat treat time
Adapted from Fig. 11.27 (a) and (b), Callister 7e. (Fig. 11.27 adapted from Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing Ed.), American Society for Metals, 1979. p. 41.)
Supersaturated α Solid Solution
Fig. 11.25.
Transition phase (θ” ) that is desirable for maximum strength
Equilibrium phase (θ) present in overaged alloy
Schematic depiction of several stages in the formation of the equilibrium precipitate (θ) phase.
Fig. 11.28. The copper-rich side of the copper-beryllium phase diagram.
Fig. 11.27a. The strength characteristics of a precipitation-hardened 2014 aluminum alloy
Fig. 11.27b. The elongation characteristics of a precipitation-hardened 2014 aluminum alloy