Welding Procedure for Aluminum
Filed Under MIG &TIG Welder Basics |
Welding aluminum can be a challenge, even for welders experienced in other metals as aluminum has quite different properties than other metals used in welding. It has a lower melting point higher thermal conductivity than steel and this can lead to burn though if the correct techniques are not used. Aluminum wire is also softer than other metals so is harder to feed when arc welding and easily becomes tangled. The following directions should help to overcome these problems.
Gas Metal Arc Welding
Base Metal Preparation
The base metal must be cleaned thoroughly to remove contamination from solvents or oils and aluminum oxide which melts at a much higher temperature than the aluminum base. This will lead to failure of the filler material to penetrate.
Aluminum oxide can be removed by carefully using stainless steel brush. Keep a seperate brush for aluminum work to avoid contamination from other metals and brush fairly gently in one direction only to avoid embedding the oxide further. If you use a chemical etching solution remove it completely before you start to weld. Clean off any oil residue with a degreaser.
Pre-heating
To help to prevent cracking of the weld the work should be preheated to a temperature of just below 230F. Be careful to avoid exceeding this temperature. If welding a thick piece of aluminum to a thinner piece pre-heat the thicker piece.
Push Technique
When welding aluminum a better weld, with less contamination can be achieved by pushing the gun from the weld rather than pulling it. This also gives better coverage of the shielding gas.
Travel Speeds
Travel speed needs to be fast for welding aluminum due to its high thermal conductivity. Aluminum needs higher amp and voltage and faster weld travel speeds to avoid burn through especially when working with thin gauge aluminum sheets.
Shielding Gas
The most common shielding gas used for aluminum welding is argon as it allows a clean action and good penetration. When using an aluminum alloy containing magnesium a shielding gas of argon mixed with up to 75% helium can be used to prevent magnesium oxide formation.
Feeding Wire
A welding wire with a similar melting temperature to the base material should be used. Narrowing down the melting range will help to achieve a better weld. Wire of diameter 3/64 or 1/16 inch should be used to make feeding easier.
Cracking Compensation
The most common cause of failure when welding aluminum is crater cracking resulting from the high level of contraction that occurs on cooling. Cracking is worse for concave craters as the surface tears as cooling occurs. For aluminum welding it is much better to use convex, mounded crater where the shape will compensate for the contraction when cooling.
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