Welding aluminum is not as easy as most people perceive it to be. You need to know different welding techniques, types of welding gases to use as well as a range of other factors that are inherent of aluminum welding. There are also pre-weld and post-weld processes that are unique to aluminum metal. Whereas it can be said that aluminum as a metal can be welded with ease, knowing the correct welding procedure is what makes the difference.
Why is Welding Aluminum Difficult?
Before even getting to the different welding processes used for aluminum metal, you also need to understand some of the challenges that you are likely to encounter in aluminum welding. Ideally, thin aluminum strips are not difficult to join. However, a major difficultly has everything to do with the filler metal. For starters, there are some aluminum alloys that cannot be welded in the absence of filler materials. In addition, there are other aluminum alloys that need to undergo solidification cracking if welding takes place without filler material. For example, 3003 aluminum and 6061 aluminum undergo the solidification process. Another major challenge that is inherent in combined metals welding is feeding. If you are still struggling with what are combined metals, aluminum welding is almost impossible. If you are using a mechanical wire feed in the process, you will need a special drive system. The reason for this is because the column strength of aluminum is less compared to that of stainless steel. In the absence of a special drive system, the aluminum is more likely to buckle and tangle. This happens especially for thin aluminum strips (i.e. 0.8 mm or 1 mm diameter).
Thermal Conductivity Properties
It is worth noting that generally, aluminum has a higher thermal conductivity compared to copper and brass as well as thin sheet metal. This basically means that the amount of heat that is initiated on aluminum is dispensed more rapidly compared to an iron-based alloy welding. This means that full penetration might not be achieved except when the process is allowed to continue for some time. This is what is referred to as the cold start. Ordinarily, thin aluminum strips might not experience a cold start. Compared to larger craters of aluminum, thin aluminum strips are less likely to experience a cold start. The metal properties in aluminum are what affect the welding process. By the time when the welding process is coming to an end, there is a lot of heat that is present on the surface which is why aluminum as a metal is very susceptible to crater cracking. Apart from when you are dealing with thin aluminum strips, craters in the metal should be filled for absolute welding.
Pre-welding and Post-welding Processes
Aluminum also happens to be one of the metals that require a pre-welding and post-welding process. During welding, aluminum tends to form an oxide layer with a higher melting point compared to the aluminum itself. So that you can avoid the presence of aluminum oxide particles that are un-melted in the weld, it is important to undertake an oxide removal process. This process should be done prior to the welding and can involve either chemical cleaning or wire brushing. There are some aluminum alloys that are artificially aged in order to increase their strength. Apart from thin aluminum strips, alloys such as 6061-T6 can be artificially aged to increase their strength. However, the strength acquired by the thin aluminum strips is greatly reduced during welding especially the heat-affected areas of the metal. This is why artificial aging should be conducted on the thin aluminum strips as part of post-welding process.