| Abstract [eng] |
This study compares two ways to weld a aluminium. The tungsten inert gas (TIG) welding process was chosen. It has three options for welding current: direct current positive electrode (DCEP), DC negative electrode (DCEN), and alternating current (AC). Every method has pros and cons and is used in the welding of ferrous or non-ferrous metals. Generally, welding manuals recommend that DC is used for TIG welding of mild or stainless steel while AC for is used for welding aluminium. Aluminium, when exposed to air, forms an oxide layer that melts at a higher temperature than base metal. An AC positive cycle where the current flows from base metal to the electrode removes surface oxides more effectively than during a negative cycle. The positive cycle acts as a surface scrub, breaking up oxides while the necessary weld penetration is achieved during the negative cycle. Both cycles work to ensure high-quality integral welds. Cleaning the weld area with a stainless-steel brush is mandatory to assure it. The control of the heat input is another challenge in aluminium TIG AC welding. However, in the case of DC, these processes are performed without the above-mentioned problems. Good, deep welds are obtained in one pass. This operation not only creates a stronger weld but also reduces the time required. DC welding finds its application in repairing deep pits and gouges in aluminium products; a pit or cavity is quickly filled with molten metal keeping the filler in the right place, ensuring solidification of the joint, which needs to be smoothed afterwards, and then the part is like new. This method makes it possible to repair expensive machined parts that are slightly damaged. Even though AC has a surface-scrubbing effect which breaks up the oxide layer, providing the possibility to obtain good welds, unlike DC current, it cannot produce integral welds. |
