heat treatment of alloys

1. Heat treatment of alloys
Rajesh Kumar S
AP/Aero
C. Abdul Hakeem College of Engg and Tech

2. HEAT TREATMENT OF ALUMINIUM ALLOY
• Wrought form of aluminium-pure form- AL1100
• High Degree of corrosion resistance but low strength
• Aluminium becomes stronger
(i) Rolled (ii) Heat treated
Formed (or)
Cold Worked
T4- Solution Heat Treated; H-strain Hardened
O- Soft or Annealed; T6-Solution Heat Treated and then
artificially aged

3. HEAT TREATMENT OF ALUMINIUM ALLOY
• Alclad Aluminium
• Pure clad
• The sheets consists of an aluminium alloy core coated with a layer of pure aluminium
• The pure aluminium coating give protection to core against corrosive agents, scratching or other
forms of abrasion.

4. Two types of HEAT TREATMENT to ALUMINIUM ALLOY
• (i) Solution heat treatment –(Al2017, Al2024)
• (ii) Precipitation Heat treatment
(Al2014, Al7075) requires both types

5. solution heat treatment
• 825 F to 980 F
• RULE: Temperature must be controlled within a very narrow range
(±10 F)
• Low temp: max. strength may not be obtained
• Excessive temp: danger of melting, the low melting constituents.
Process:
(i) Soaking:
time at temperature,
soaking time: measured as the time the coldest metal
reaches the minimum desired temperature range
(i) Quenching:-cold water, Hot water, Spray quenching, Lag b/w
soaking and Quenching (10 sec)

6. Precipitation hardening
• 3 steps:
• Solution heat treatment
• Quenching
• Precipitation Heat Treatment

7. Precipitation hardening
Aluminium
Magnesium
Nickel
Titanium
Some steels and stainless steels
Aging:
Alloys can be kept at elevated temperature for hours to allow precipitation to
take place. This time delay is called aging.
SHT: involves formation of a single phase solid solution via quenching
PHT: involves the addition of impurity particles to increase material’s strength.

8. HEAT TREATMENT OF magnesium ALLOY
• 95% of Mg used in aircraft construction is in cast form
• Heat treatment is similar to Al alloy
(i) Solution heat treatment
(ii) Precipitation heat treatment
• Change in properties is negligible when allowed to age naturally at
room tempratures.

9. solution heat treatment of MAGNESIUM ALLOY
• Magnesium alloy casting-SHT
• To improve tensile strength, ductility and shock resistance
• T4-
• T6-
• Solution heat treatment
• Solution heat treatment + ARTIFICIAL aging
• Artificial aging is necessary to develop full properties.
• 730 F to 780 F
• Soaking time: 10 to18 hr……………….(longer than 18 hrs…more than
2inch thick)
• NEVER heat a magnesium alloy in a salt bath- explosion
• Fire hazard exists in SHT of magnesium alloy (protective atm of SO2)

10. precipitation heat treatment of MAGNESIUM ALLOY
• To increase hardness and yield strength
• Relieve stresses
• Stabilize alloys
• Amount of ductility reduced
• Corrosion resistance also improves
• Lower temp range than SHT (325 F to 500 F)
• Soaking time 4 to 18 hrs

11. HEAT TREATMENT OF TITANIUM ALLOY
PURPOSE
• Relief of internal stresses
• Annealing – to provide maximum ductility
• Thermal Hardening - to improve strength
• Case hardening

12. Heat treatment of TITANIUM ALLOY
• STRESS RELIEVING
• To remove stress concentration – 650 F to 1000 F
• Time at temperature: (few minute to an hour or more for heavier sections)
• Scales or discoloration removed by pickling in acid solution.
10 to 20% HNO3 and 1 to 3% hydrofluoric acid
• FULL ANNEALING
• Toughness, Ductility at room temperature, dimensional and structural
stability, Improved machinability.
• 1200 F to 1650 F
• Time at temperature: 16 min to several hours
• Scales or discoloration : Use of caustic descaling –sodium hydride salt bath.
• THERMAL HARDENING
• Unalloyed titanium cannot be heat treated.
• Most of alloys strengthed by heat treatment
• Sacrificing ductility
• Water quenching from 1450 F followed by reheating to 900 F , 8 hours

13. Heat treatment of TITANIUM ALLOY
• CASE HARDENING-
• Nitriding, carburizing and carbonitriding
• Wear Resistance case of 0.0001 to 0.0002 inch

14. Melting point of ALLOYs
• Carbon – 3540 C
• Titanium – 1650 C
• Aluminium – 660 C
• Magnesium – 650 C
• Mild steel – 1370 C

15. Soaking
Temperature
Time at temperature
Soaking Time
AL-SHT
AL-PHT
825 F to 980 F 10 min to 12 hours
Mg-SHT
Mg-PHT
730 F to 780 F
325 F to 500 F
10 hours to 18 hours
4 hours to 18 hourss
Ti- SHT
Ti-PHT