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A calorimetric study of gas tungsten arc welding of aluminium is described. The present study comprised experiments in which autogenous welding runs were each made on a block of electrical conductor grade aluminium. The blocks were all approximately cubic in shape which, when combined with the high thermal conductivity of aluminium, ensured that their temperature equalised soon after the completion of a run. Each sample was immersed in insulating material before welding so that heat losses to the surroundings were minimised. Thermocouples were attached to the block in each experiment and the bulk temperature rise was related to the energy input associated with the welding run. The effects of arc polarity, alternating current balance, shielding gas composition, arc length and welding current on the arc power and arc efficiency were investigated. The results obtained with alternating current are compared to those for direct current, and the differences are explained.

A variant of the friction stir welding technique developed at TWI, called Skew-stir (tradename) was applied to the welding of lap joints in Al alloy AA5083–0. This technique differs from the conventional method in that the axis of the tool is given a slight inclination, or skew, to that of the machine spindle. It is particularly advantageous in instances where a wide weld region is required, such as lap joints in which the interface is perpendicular to the machine axis. The microstructures and mechanical properties of welds made using both a conventional pin type probe and the rotary Skew-stir technique with an A-Skew (tradename) probe were studied. The joints made using the Skew-stir technique sustained significantly higher tensile loads and had longer fatigue lives compared with those made using the conventional pin type probe.

Type IV cracking refers to the premature failure of a welded joint due to an enhanced rate of creep void formation in the fine grained or intercritically annealed heat affected zone. A great deal of research effort has been directed at understanding the underlying mechanisms for this type of failure, but most have approached the problem from a metallurgical standpoint, and comparatively little effort has been directed at understanding the effects of welding variables. Here the effects of parameters such as the preheat temperature and heat input on the tendency for type IV failure in 9-12%Cr steels have been quantitatively estimated. These calculations have subsequently been verified experimentally to form the first systematic study of welding parameters on type IV cracking. The joint geometry and preheat temperature have been found to ameliorate type IV failures, while the effect of heat input is less significant.