A normal concern of engineers when designing parts proposed for welding is how strong the welded joints will be. Will they be stronger than the base metal?
If you design your joints correctly and you have a skilled welder performing the job, your resultant welded joints will definitely be as strong as the parent materials they are joining.
Achieving reliable simulation on welded can be quite difficult at times. This is due to the numerous associating variables such as welder expertise, weld thickness, technique applied and type of weld. In this article, I’ll explain the strength and kinds of welds, and also compare a finished weld to its base metal.
How Strong Are Welds?
How strong a weld becomes, is partly determined by how pure the base materials are before the weld is designed. You need to make sure your workpieces are void of foreign pollutants, grease or oil. Cold-rolled steel parts do require a moderate amount of cleaning, but hot-rolled steels will demand special cleaning.
Aluminum alloys need etching or wire brushing prior to welding. This helps to remove oxidation and produces superior quality welds.
What Are the Kinds of Welding?
There are two popular kinds of welding. They are Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG):
Metal Inert Gas (MIG): Met inert Gas (MIG) welding creates a bend between an endlessly fed wire filler metal and the metallic workpiece. Both the shielding gas and the molten metal get protection from atmospheric contaminants. Many metals and alloys can be processed with this metal inert gas technique.
Tungsten Inert Gas (TIG): Tungsten inert gas welding generates an arc between the workpiece and a non-inflammable tungsten electrode. You use Inert gas to protect the arc and the workpiece, so you may or may not use filler metal. Like MIG, TIG is efficient in joining most alloys and metals, but it yields better quality welds due to the absence of weld spatter.
In contrast to MIG, TIG can be used to generate fuse-welded joints if there is no filler metal, resulting in a slight eruption above the parent metal. It is possible to create welds in various positions, but this technique is a bit slower than other welding methods. Typically, TIG takes at least twice as long to finish the same type of weld.
Is a Weld Stronger Than the Metal?
The authorized stand of materials science is that if a weld is properly created, it is at least as strong as the original metal. This view can be misleading because even though a weld has a higher tensile capacity, it is usually less malleable which implies it loses some firmness. Firmness in this context has a particular implication which is the result of tensile strength and malleability.
Toughness is a great judge of how much power a part can take up before breaking. This implies that although a weld is “tougher” as judged by tensile capacity, it comes at the price of malleability and usual firmness. In a more practical sense, this means that if a weld is put in a test rig, it will demand additional capacity before it fails.
In a situation where the part is lodged, the failure often occurs near the weld. Although the mechanism behind this phenomenon is complex, it is essentially a function of the weld’s varying elasticity in relation to the mass and strength of the material. The force gets condensed on the areas close to the weld because it doesn’t arc at the same rate with the workpiece.
Due to these complex factors, a component welded from a bulk of material would have a better performance than a part produced from two elements welded together.
How Does a Weld Become Stronger Than the Parent Metal?
From a mechanical view, the material the welding rods consist of possess stronger properties such as tensile and yield strength, than the material worked on. This means that that part of the concluded assembly will be stronger than the rest. Note that the weld itself may be tougher than the parent metal due to variance of materials used.
When you weld, you produce a temperature slope from the weld point to the unchanged material. The temperature is hottest at the weld and cools off towards the end of the base metal. When this occurs, you are actually hardening the metal, as these temperatures can be way above strengthening temperatures.
In some cases, depending on how the weld was created (cooling and post-temperature treatment) you can get single cell conversion from one form to another. For example, creating a body focused cubic to a face centered cubic. So even if the weld itself is stronger, the material encompassing the weld will now become the fragile point of the material.
However, the loss of strength that comes with the heating and cooling process doesn’t account for the capacity to produce a galvanic cell (rapid corrosion). Then the galvanized unit is created at that location because of the distinct metals, and any air immersion gradients that may have formed. It also includes any oxides or hydrides which may have shaped during the procedure.
Again, while the weld on its own may become tougher than the base material, it is quite common for materials to lag. Due to the reasons discussed above, this occurs at the welded location, which is why a skilled welder is priceless. Overall, it isn’t as a result of the separation of alloying components that occurs in the process of solidification.
Lastly, It could be a cast microstructure. As part of normal steel processing, the filler metal components are slightly different from the parent metal. It results in a quality weld strength. Also, depending on the components, some alloys have a heat dirce to increase the malleability and forgo ultimate strength.