Porosity is among the most common defects associated with welding as a metal fabrication technique. The welding exercise results in the production of nitrogen, hydrogen and oxygen gas. These gases are absorbed into a molten weld pool and they're released before the molten weld solidifies. Weld porosity occurs when quantities of the mentioned gases remain trapped in the weld metal after the molten weld has solidified.
A homeowner looking to piece together an aluminium frame for their residential carport needs to understand the common causes of this weld defect and possible ways to prevent the occurrence of porosity.
Contamination of aluminium is among the most common causes of porosity that a DIY-minded homeowner should be keen to avoid.
Aluminium metal is considered to have been contaminated if it contains various impurities on its surface. For example, the surface of an aluminium carport frame is likely to have contaminants such as oil and grease. The presence of these contaminants encourages the formation of an oxide layer on the surface of the frame, thereby increasing the chances of porosity in the weld metal.
Before welding-related activities can commence, DIY-minded homeowners are advised to clean the aluminium frame using an appropriate cleaning technique (e.g. chemical etching or mechanical cleaning) so as to reduce the likelihood of a porous weld. After the frame is clean, it should be welded immediately so as to prevent the re-formation of the oxide layer.
A DIY-minded homeowner will use a shielding gas (e.g. nitrogen or helium) so as to protect the welded portion of the carport frame from the infiltration of moisture and from the possible damaging effects of the frame being exposed to oxygen gas.
There is great importance attached to using the right quantity of shielding gas/gases when welding an aluminium carport frame. If too much of the shielding gas is used around the molten weld, quantities of this gas can easily get trapped in the aluminium frame before the weld solidifies.
Luckily for the DIY-mind, manufacturers of welding equipment often specify the right amount of shielding gas recommended for use with their equipment. This information will often be contained in the instruction manuals that come with the equipment.
Porosity also occurs when the shielding gas fails to reach the molten weld pool. For example, this may happen when a homeowner chooses to weld the carport frame next to an external air conditioner whose operation can blow the shielding gas away from the molten weld pool.