The Effect of Hydrogen on Aluminum Welding

Of all gases, only hydrogen is soluble in aluminum. However, compared to the solubility of gases in iron alloys, the solubility of hydrogen is quite low.

The solubility of hydrogen in aluminum depends on the composition of the alloy and the temperature. The amount dissolved is generally expressed as partial pressure and depends on the volume of dissolved gas in milliliters per 100 grams of metal. (At 1013 mbar and 0°C, 1 ppm = 1.1124 ml/100g)

Since the solubility of hydrogen in aluminum drops abruptly at a temperature of approximately 600°C, this typically leads to porosity problems during cooling due to the freezing of gas bubbles. Pure aluminum is the material with the highest tendency for porosity; in alloys, this tendency is lower. This is due to a smaller change in hydrogen solubility.

These conditions make porosity in aluminum MIG welding nearly inevitable. Porosity can negatively affect the static and dynamic strength of welded joints and create aesthetic issues. In addition, porosity on the surface can cause cosmetic defects and reduce paint adhesion.

Inspectors may have difficulty determining an acceptable level of porosity, and both manufacturers and customers often view this as poor workmanship.

The fundamental solution to this problem is to keep the hydrogen content as low as possible. A hydrogen content typically ranging from 0.2 to 0.3 ml/100g is generally considered the maximum acceptable level for achieving low porosity. However, this value is frequently exceeded under practical conditions. Sources of hydrogen include the base material, filler material, shielding gas, and the surrounding atmosphere. Maintaining clean storage and production conditions, proper surface preparation, and preventing all other sources of hydrogen are the most important guidelines.