The welding of aluminium and its alloys

Rectification of distortion

If the measures listed above are not effective, remedial measures to rectify the distortion will be necessary. These may be based upon those used for steel but great care needs to be exercised if such techniques are used. The most effective methods are those that use some form of mechanical working or stretching as these will not significantly affect the mechanical properties of the base materials. Longitudinal bow in welded beams should preferably be done cold by pressing, and buckled plate may be pressed flat.

As a last resort, local spot or line heating may be used to heat-shrink items that have been distorted by the welding of, for instance, stiffeners. Some examples of how these techniques can be applied are illustrated in Fig. 5.24. The high thermal conductivity of aluminium means that local heating with an oxy-gas torch is not very effective. If this technique is to be used then electric induction heating is the most effective method of intro­ducing sufficient heat into the component.

If heat must be used then this should not exceed 400 °C for the non-heat treatable alloys. Remember, though, that temperatures over 250 °C will produce full softening in the alloy if it is in the work-hardened condition. The age-hardened heat-treated alloys should not be heated to more than 150 °C as this will cause softening due to overageing of the precipitates.

Whenever these techniques are used then reference must be made to the design engineer to ensure that the potential loss of strength is taken into account.

The welding of aluminium and its alloys

Alloy designations: wrought products

Table A.4 BS EN BS EN Old BS/DTD Temperature (°C) numerical chemical number designation designation Liquidus Solidus IVIdUng range Al 99.99 1 660 660 0 AW-1080A Al 99.8 1A AW-1070A …

Principal alloy designations: cast products

Table A.3 BS EN numerical designation BS EN chemical designation Old BS number ANSI designation Temperature (°C) Liquidus Solidus Melting range Al 99.5 LM0 640 658 18 AC-46100 Al Si10Cu2Fe …

Physical, mechanical and chemical properties at 20°C

Table A.2 Property Aluminium Iron Nickel Copper Titanium Crystal structure FCC BCC FCC FCC HCP Density (gm/cm3) 2.7 7.85 8.9 8.93 4.5 Melting point (°C) 660 1536 1455 1083 1670 …

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