As the electric current is relatively large when soldering aluminum, the tungsten electrode is more likely to be dissipative at the long-lasted temperature. So the thicker tungsten electrode is advised to use. When using a-c argon welder, turn down the current and use 3 cm electrode.
In addition to size, type affects too. It is noted that the component of tungsten electrode is distingushed by particular color code. When soldering aluminum / aluminum alloy, tungsten electrode with green head is well recommended.