Welding involves the art & science of joining materials, typically metals, through the application of heat and pressure. The process demands a deep understanding of the properties of different metals, the intricacies of welding techniques, and the interplay between these factors.
In this guide we will discover what metals cannot be welded. So stay tuned-
Weldability Defined
Weldability refers to the ease with which a particular metal can be successfully joined or welded with a certain procedure.
Metals are considered weldable if they can be easily and simply welded. And provided that, precautions such as metal preparation, preheating, controlled cooling & specific heat treatment are required before welding, then the material is considered non-weldable.
The concept of weldability encompasses a range of factors. Such as melting point, thermal conductivity, chemical composition, ductility and toughness, cleanliness and hydrogen embrittlement.
Issues In Welding Incompatible different materials
You can weld any similar metals easily. The problem arise when you try to weld dissimilar metals and metal alloys. There are two issues that create difficulties in welding. And they are
- Welding process &
- Metal combination
When you plan to do fusion welding to join incompatible materials, challenges arise.
- Intricate metallurgy of each base material can hinder the robust joints of metals which is one of the problems.
- Moreover, contrast in melting point between two materials results in unsound joint formation.
- Distinctions in thermal expansion coefficients, thermal conductivity, and specific heat exist between the two materials complicates the whole process either.
What Metals Can Not Be Welded
Here are a few examples of metals that are challenging to weld:
- Hg (Mercury): Mercury is a liquid metal at room temperature, which makes traditional welding methods impractical. Due to its low boiling point, attempting to weld mercury would result in vaporization rather than a solid joint.
- Na (Sodium): Sodium is highly reactive with moisture and air. When exposed to these elements, sodium forms oxides and hydroxides, making it challenging to achieve a clean, stable weld. The reaction with water also produces hydrogen gas, posing safety hazards.
- Cs (Cesium): Similar to sodium, cesium is highly reactive and can combust upon contact with air. Welding cesium is not practical due to the risk of fire and the metal’s extreme reactivity.
- Fr (Francium): Francium is an extremely rare and highly radioactive alkali metal. Its scarcity and radioactivity make it practically impossible to handle for welding purposes. Moreover, francium rapidly decays into other elements, further complicating any attempt at welding.
- Ga (Gallium): Gallium has a unique property of remaining in a liquid state near room temperature. While it solidifies at slightly higher temperatures, the liquid phase at common welding temperatures poses challenges for creating stable welds.
- Ru (Ruthenium) and Os (Osmium): These platinum group metals have extremely high melting points, making them difficult to weld using conventional methods. The temperatures required to melt these metals are beyond the capabilities of standard welding equipment.
- Re (Rhenium): Rhenium has one of the highest melting points of all elements, making it challenging to weld. Its exceptional hardness and brittleness further complicate the welding process.
- Magnesium: Magnesium, valued for its low density and high strength-to-weight ratio, poses challenges in weldability due to its high reactivity with oxygen. Specialized techniques, including the use of inert gas protection and precise heat control, are essential for successful magnesium welding. The low melting point of magnesium demands careful handling to prevent overheating and avoid weld porosity.
- Tin: Tin, often used as a coating or alloying element, is generally considered non-weldable in the traditional sense due to its low melting point. With a melting point of just 231.93°C (449.474°F), attempting to weld tin can result in rapid and complete melting rather than forming a stable joint. As a result, joining techniques such as soldering, which utilizes lower temperatures, are typically preferred for working with tin.
- Lead: Lead is non-weldable in conventional terms due to its propensity for complete melting at just 327.46°C (621.428°F). As a result, traditional welding processes are not suitable for lead. Instead, lead is commonly joined using alternative methods like soldering, where lower temperatures are employed to create a reliable bond.
There are also few alloy and metal combinations that creates complications in fusion welding. For example- steel (stainless or carbon) and aluminum, copper and aluminum, steel and titanium are few combinations which can’t be welded without altering the properties of the materials.
Solution To The Problems
There are few options open for a welder to join two non-weldable metals.
- By modifying the welding technique you may be able to weld various combination of metal. If fusion welding technique cannot provide the solution then you have many options like
- mechanical fastening,
- brazing,
- adhesives (JB weld),
- soldering,
- solid state welding (friction, ultrasonic, magmatic pulse, explosion weld etc.)
- Diffusion bond
- You may go for mix option or combination of welding techniques also. For example: Suppose you are trying to join a stainless steel tube to aluminum tube. You may use a bimetallic transition part where one portion is 100% stainless steel and another portion 100% aluminum. Now you may friction weld the bimetallic part and then arc or mig weld the stainless part of transition part to the base stainless steel tube and aluminum part of transition part to parent aluminum tube.
- If changing process is not possible, then only one way is out and that is to change at least one material. But in few case metals are not weldable no matter what technique you apply.
- If it doesn’t work, then you have to modify the metal combination. For example you may melt & cast the metals and change the properties for fusion purpose.
Conclusion
It’s important to note that advancements in technology and specialized welding techniques may overcome some of these challenges.
However, in practical terms, welding certain metals may not be feasible or may require unconventional methods due to safety concerns, extreme reactivity, or the limitations posed by the physical properties of the metals.
Related Articles
Sources
- industrialmetalsupply.com/blog/what-metals-can-be-welded
- makeitfrommetal.com/can-steel-be-welded-to-aluminum/