Treatment of Aluminium Alloys
Involves Softening,Annealing,Tempering,Hardening,Material Modifications.|
Softening: Softening is done to reduce strength or hardness, remove residual stresses, improve toughnesss, restore ductility, refine grain size or change the electromagnetic properties of the steel.
Hardening: Hardening of steels is done to increase the strength and wear properties. One of the pre-requisites for hardening is sufficient carbon and alloy content. If there is sufficient Carbon content then the steel can be directly hardened. Otherwise the surface of the part has to be Carbon enriched using some diffusion treatment hardening techniques.
Material Modification: Heat treatment is used to modify properties of materials in addition to hardening and softening. These processes modify the behavior of the steels in a beneficial manner to maximize service life, e.g., stress relieving, or strength properties, e.g., cryogenic treatment, or some other desirable properties, e.g., spring aging.
Most aluminium castings are used in the 'as cast' condition, but there are certain applications that require higher mechanical properties, or different properties from the as cast material. The heat treatment of aluminium castings is carried out to change the properties of the as cast alloys by subjecting the casting to a thermal cycle or series of thermal cycles. For sand castings and gravity die castings all heat treatments are possible, though not all are standardised. Pressure die castings however, cannot generally be heat treated.
The following are the suffixes used in the USA/UK to indicate the heat treatment condition of ASTM B179/BS1490 Aluminium Alloys:
The following alloys are not fully heat treated: LM0, LM2, LM5, LM6, 413.2/LM20, & LM24.
The following alloys may be heat treated, but their properties are not standardised in the heat treated condition shown: LM12, 319.2/LM21, 328.1/LM27-TF & LM30-TF.
The following alloys are standardised in the heat treated conditions indicated: LM4-TF, LM9-TE, LM9-TF, LM13-TE, LM 13-TF, LM13- TF7, LM16-TB, LM16-TF, LM22-TB, LM25-TE, 356.0/LM25-TB7, LM25-TF, LM26-TE, LM28-TE, LM28-TF, LM29-TE, LM29-TF, LM30-TS.
M As cast
TS Thermally stress relieved, annealed
TB Solution heat treated and naturally aged to a substantially stable condition
TB7 Solution heat treated and stabilised
TE Artificially aged
TF Solution heat treated and artificially aged
TF7 Solution heat treated, artificially aged and stabilised
LM31 is a naturally ageing material, which may also be artificially aged. The application of the term heat treatable to aluminium alloys, both wrought and cast, is restricted to the specific operations employed to increase strength and hardness by precipitation hardening thus the term heat treatable serves to distinguish the heat treatable alloys from those alloys in which no significant strength improvement can be achieved by heating and cooling.
Temperature Ranges: 500°C, 650°C, 700°C
Heavy Duty heat treatment ovens, suitable for annealing, stress relieving or tempering of aluminium, ferrous metals, brass, copper and glass. Some typical applications would be:
Heat treating aircraft parts to Boeing and Rolls-Royce specifications.
Heat treating springs and plated parts Curing sermetal coated components.
treating for aluminum alloys is frequently restricted to the specific operations
employed to increase strength and hardness of the precipitation-hardenable
wrought and cast alloys. These usually are referred to as the “heat-treatable”
alloys to distinguish them from those alloys in which no significant strengthening
can be achieved by heating and cooling.Heat treatment to increase strength
of aluminum alloys is a three-step process: |
Solution heat treatment: dissolution of soluble phases
Quenching: development of supersaturation
Age hardening: precipitation of solute atoms either at room temperature (natural aging) or elevated temperature (artificial aging or precipitation heat treatment).
Heat Treatable Aluminum AlloysSolution Heat TreatingPrecipitation Heat Treating without Prior Solution Heat Treatment
QuenchingAge hardening Precipitation heat treatments