Aluminium annealing
Types of aluminium annealing
Aluminium annealing have several types that differ in obective [1]:
- full annealing
- partial annealing
- stress-relief annealing
- stabilizing annealing
- controlled-atmosphere annealing.
Annealing times and temperatures depend on:
- alloy type
- initial structure and temper.
Full annealing
- The softest, most ductile, and most workable condition of both non-heat-treatable and heat-treatable aluminium alloys
- Temper designation: O temper
Typical annealing conditions used for some alloys in common use are shown in the table of Figure 1.
Figure 1 – Typical full annealing treatments for some common wrought aluminium alloys [1]
The treatments, which are listed in the table, anneal the material to the O temper. They are typical for various sizes and methods of manufacture. So, they may not exactly describe optimum treatments for specific products.
The instructions in the table of Figure 1
The instruction (a):
- Time in the furnace need not be longer than necessary to bring all partsof the load to annealing temperature.
- Cooling rate is unimportant.
The instruction (b):
- These treatments are intended to remove the effect of solution treatment.
- Included cooling at a rate of about 30 ⁰C/h from the annealing temperature to 260 ⁰C.
- Rate of subsequent cooling is unimpotrant.
- Treatment at 345 ⁰C followed by uncontrolled cooling, may be used to remove the effects of cold work or to partly remove the effects of heat treatment.
The instruction (c):
- These treatments are intended to remove the effects of solution treatment.
- Include cooling at an uncontrolled rate to 205 ⁰C or less, followed by reheating to 230 ⁰C for 4 h .
- Treatment at 345 ⁰C followed by uncontrolled cooling, may be used to remove the effects of cold work or to partly remove the effects of heat treatment.
The instruction (d):
- Cooling rate to 205 ⁰C or below is less than or equal to 30 ⁰C/h.
Partial annealing
- Another name is recovery annealing
- Partial annealing is the heat treatment of cold worked, non-heat-treatable wrought alloys to obtain intermediate mechanical properties for H2 tempers)
- Temperature used are below those that produce extensive recrystallization.
- Incomplete softening is accomlished by substructural changes in dislocation density and rearrangementsinto cellural patterns.
Figure 2 shows changes in yield strength as functions of temperature and time for sheet of two non-heat-treatable alloys (1100 and 5052). Initialy these alloys were in the highly cold-worked condition (H18 temper).
- Heat Treating / Aluminum and aluminium alloys // ed. J.R. Davis – ASM International Handbook – 1993
