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There are many considerations when developing welding procedures for aluminum. This paper will concentrate on two variables:

1. Distortion is of concern for manufacturing weldments where tolerances are critical. Aluminum, when compared to steel, has a greater propensity for distortion due to the high coefficient of thermal expansion intrinsic to the material. The distortion that occurs within a weldment is in correlation with the total heat input of the weldment.
2. In general, multi-pass aluminum welds will result in more total heat input than a weld of the same size but done in a single pass. This would suggest that one could increase the weld size per pass, rather than implementing a multi-pass procedure, in order to reduce weld distortion. However, simply increasing the weld size per pass can result in other weld defects such as lack of fusion and greater material degradation within aluminum.

This paper proposes that considering a specific weld size for aluminum, less material degradation and a more mechanically sound weld will occur with the weld using multiple passes in correlation with the heat input per pass, not the total heat input of the welded joint.

CSA W59.2-M1991 (R2008): Welded Aluminum Construction does not define the maximum fillet weld size per pass for electrode diameter and welding position. This study will present data relevant to the choice faced by many aluminum welding fabricators: to choose (i) multiple-pass or (ii) single pass to achieve a desired weld size with the best mechanical properties. This project will investigate welds performed using both methods and will propose maximum fillet weld sizes per electrode size and welding position.