Identification Of Heat-Treated Aluminium Alloys

Aluminium alloys that have been subjected to heat-treatment are usually identified by markings that indicate the heat-treatments involved. Three typical identification systems are those of the British Standards Institute (BS), the Ministry of Supply (MoS), and the American systems as can be seen below,


Identification Markings of Heat Treated Aluminium Alloys

BS System Meaning
M As manufactured state
O Annealed state
OD Annealed and lightly drawn
T Solution-treated, no precipitation required
W Solution-treated, can be precipitated
WP Solution-treated and precipitation treated

MoS System Meaning
A Annealed state
N Solution-treated, no precipitation required
W Solution-treated, and requires precipitation
WP Solution-treated and precipitation treated

American System Meaning
T3 Solution-treated and cold worked
T4 Solution-treated only (naturally aged)
T6 Solution-treated and artificially aged
T8 Solution-treated, cold worked and artificially aged
T9 Solution-treated, artificially aged and cold worked

An example of one of these marking systems would be an alloy with the designation 2024-T4, which indicates an aluminium/copper alloy that has been solution-treated only, and then naturally aged

Apart from these systems, many other exist world-wide, but the British systems are broadly confined to the following for light alloys.

• British Standards for general engineering use BS 1470 -1475. In this series the prefix N is used to denote non-heat-treatable aluminium alloys and prefix H for the heat-treatable alloys.

• British Standards for aerospace use the L series such as BS 3 L72, which indicates the 3rd amendment to the basic L 72 specification whilst LM indicates a cast material. The wrought materials are commonly abbreviated to L71, L72 and L 73 et al.

Examples of some of these aircraft BS codes are:

• 159 Dural Solution-Treated and Artificially aged
• L163 Alclad Solution-Treated and Naturally aged

Dural is a Trade name for an 2017 Al/Cu/Mg/Si/Mn alloy, originally manufactured by the Duren Aluminium Company (Germany) for the Zeppelin Airships. It is often used as a generic name for similar alloys, regardless of source of manufacture.

DTD Specifications are material identification numbers issued by the Directorate of Technical Development (a Ministry Department) for specialised applications, when widespread use is not anticipated. If such a material finally becomes commonly used, a British Standards specification is compiled and issued.

Aircraft Control Cable Tensioning

The correct tension for a control cable is specified in the Aircraft Maintenance Manual.  It is checked using a tensiometer and adjusted using the turnbuckles.

The tensiometer must have the riser installed that is specified for the cable size being checked.  The cable is slipped between the riser and the two anvils.  The lever is then closed against the housing.  The reading on the scale is then applied to a chart to obtain the cable tension.  A pointer lock can be used to hold the instrument reading while it is being removed from the cable.  The tension is checked when there is no load on the controls and in the middle of the longest stretch of cable between pulley.

Before using the tensiometer make sure that the serial number of the chart is the same as that of the tensiometer.  Make sure that the tensiometer is ‘in date’ ie. not due for calibration.

Changes in temperature will affect the tension of the cables and this must be taken into account when adjusting the cable tension.  It is usual for a temperature/tension graph to be given by the aircraft manufacturer.  Using the graph, the correct tension can be applied to the cable.  In colder countries the required load will be lesser as compared to the hotter countries, this is mainly due to temperature effect on materials which causes it to expand or contract.

An example of a graph is shown below.