Hobbyists may have heard experienced fabricators saying that it may not be necessary to preheat aluminium when one is going to weld it. However, other fabricators may have said that one can preheat aluminium before welding it. Such contradictory information can make it hard for an inexperienced hobbyist to decide when he or she should preheat aluminium. This article discusses when it may be necessary to preheat aluminium before you start welding it.
Possession of Low Wattage Equipment
Aluminium is known for its high capacity to conduct heat. This high conductivity can make it very challenging to weld a thick sheet of aluminium if you own low-power welding equipment. This is because the limited heat generated by your welding equipment is likely to be conducted quickly away from the weld zone. Consequently, the quality of your welds is likely to be low. For instance, the weld joint will have some gaps at the points where heat was conducted away before the two layers could melt and fuse at the joint. You can overcome this challenge by preheating the material before you start welding it. The higher temperature of the entire material will limit how quickly the heat generated by your welding equipment can be conducted away from the weld zone.
When Humidity is High
Moisture can increase the porosity of aluminium welds. This is because the trapped moisture can release hydrogen bubbles that prevent the aluminium sheets from adhering to each other effectively during the welding process. Preheating the aluminium before you start welding it can be very helpful in getting rid of the condensation or water vapour that can cause the welds to be porous.
Welding Sheets with Varying Thicknesses
Preheating aluminium can also be necessary in case the materials that you are welding differ in their thickness. How can this be helpful? The thinner material is likely to melt faster than the thicker material. This imbalance in the rate of melting can cause the weld joint to be weak because the two materials will not fuse well. Preheating the thicker material ensures that it will melt at the same rate as the thinner material so that they fuse well during the welding process.
Remember that care must be taken when preheating aluminium so that excessive preheating does not compromise the mechanical properties of the metal. Avoid this defect by making sure that the aluminium alloy that you are welding isn't susceptible to stress corrosion cracking. Seek for guidance from a provider of metal fabrication services in case you have any queries about the suitability of preheating for the aluminium alloy that you are using in your DIY project. For instance, you may need to confirm whether the wattage of your welding equipment is sufficient for the thickness of the aluminium sheet that you wish to weld.