Heat Treatment of Aluminium Alloys

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 UK to indicate the heat treatment condition of BS1490 Aluminium Alloys:

• 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

The following alloys are not fully heat treated: LM0, LM2, LM5, LM6, LM20, & LM24.

The following alloys may be heat treated, but their properties are not standardised in the heat treated condition shown: LM12, LM21, 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, LM25-TB7, LM25-TF, LM26-TE, LM28-TE, LM28-TF, LM29-TE, LM29-TF, LM30-TS.

LM31 is a naturally ageing material, which may also be artificially aged.

Heat Treatment of Zinc Alloys

Zinc alloys are not generally heat-treated, but annealing of ZA27 alloy considerably improves ductility.