The Rise of Metallurgy and a Look at Materials Joining Technology
Metallurgy is one of the most important sciences in modern engineering. Specifically, it's the science of extracting metals from the ores where the metals are found and then modifying the metal to be more useful.
You can think of the science of metallurgy as a combination of physics, chemistry, and a little bit of engineering.
To understand this realm of science and how it came to be, let's take a look at the history of Metallurgy.
The modern usage of metals didn't come easily. In fact, our modern ability to work with metals so accurately is the result of nearly 7,000 years of development.
The first metals discovered were gold, silver, and copper, which are all found in their natural metallic state. This means that ancient cultures would've been able to find these metals and start working with them with very little modification.
Gold specifically can be combined together with other pieces into one larger piece through cold hammering. This made gold a fairly easy metal to work with. During the metal age, civilizations made the discovery that copper could be melted down and cast into shapes around the 4th Millennium B.C.
During this time period, we started seeing copper axes come into prominence.
Metalworking now became a process beyond cold-hammering, moving into casting, and forging. It was following this discovery of heating metals that it was found that some metals could be recovered from minerals.
This discovery of non-metallic state metal lurking in minerals would slowly yield the discovery of the smelting process involving heating copper to temperatures higher than 700°C. This process was also the first time that ancient civilizations started introducing new minerals and elements to the metallurgy process to purify the metal and alter its process.
To recap, it's best to think of the history of metallurgy as an evolving process. First, there were metallic metals discovered that could be worked together without heat. Next, it was discovered that metals could be cast through a melting and hardening process.
Then, civilizations realized that metals could be recovered from minerals – with the final stepping stone being the discovery of metal additives or alloys. This leads us to look into the history of one of the first alloys: bronze.
Bronze first appears to have been discovered as a copper alloy around 3000 to 2500 B.C. The metal is a copper alloy with about 12 percent tin. Bronze was one of the first alloys ever discovered as civilizations started experimenting with mixing elements in metallurgical processes.
Tin was the primary discovery that led to the formation of bronze as a workable metal. It's believed that at first, this metal was made in small localities, but knowledge of it eventually propagated because of trade throughout the Middle East and Europe.
As the growth and dominance of bronze through the Bronze Age continued, eventually Iron was discovered, leading to a new age: the Iron Age.
There's not really a concrete turning point between the bronze and the iron age, rather a gradual transition. One of the earliest pieces of iron ever discovered was found in the Netherlands and dates back to 1350 B.C. Traditionally, this time period would've been considered the middle of the bronze age, so it appears that both metals were produced in conjunction for some time.
Iron really reached dominance by about 1000 B.C. as it was then being fashioned into large scale weapons. This transition likely started around 1200 B.C. — usually, the time marked as the beginning of the Iron Age.
Early civilizations developed a process of melting iron oxide with charcoal. However, at the time, metalworkers couldn't achieve the high temperatures of 1,540 °C that were needed to smelt the elements together fully. This process created a spongy mass of metal mixed with a liquid-like slag. Metalworkers would repeat the low temp smelting process over and over again until it created wrought iron, a more workable iron product. The interesting note (as archaeologists studied the Iron Age) was pinpointing exactly when the process of adding carbon to strengthen iron began.
As early metallurgy techniques involved low temps, the result of burning the iron with charcoal was pure iron. As the furnaces of the time improved and the temperatures increased, more carbon was absorbed into the iron – unintentionally. This result wasn't consistent, so much of the iron at this time had a wide variety of carbon inside.
As ironwork got more refined, so too did the knowledge of carbon's effect on iron. Carbon infused iron could be made harder by quenching the metal.
However, during the early Iron Age, there is little evidence that this process was carried out as the iron needed to both be quenched then tempered in order to take advantage of the increased strength.
Rather than the process of quenching and tempering, archaeologists have seen that iron-age metalworkers took on a process of cold forging to strengthen the metal.
From the iron age onward, there was a significant development in how metals were refined and forged, which has continued on into the modern era.
To learn a little bit more about different metallurgical processes, take a look at this video:
Now that we've covered the rise of metallurgy let's take a look at some materials joining techniques used with modern metals, specifically in the realm of welding.
Welding is a very broad term covering hundreds, if not thousands of specific materials joining processes. Even if you are not a welder by trade or a materials joining engineer, understanding how various materials can be joined is crucial to excelling in your engineering profession.
To start off our understanding of welding processes, let me throw out a bunch of acronyms and terms, then we can dive into specific processes a little later on.
The main welding processes are shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW/TIG) gas metal arc welding (GMAW/MIG), flux-cored arc welding (FCAW), submerged arc welding (SAW), electro slag welding (ESW), and lastly resistance welding.
Did you get all that?
Those are only the basic welding methods, and there are many different variations of each, along with techniques that weld using friction, lasers, or even electron beams.
Each process is specifically designed for different metals, and there are even processes that can weld dissimilar metals. There’s no way we can cover an extensive review of all the welding processes in this blog post, but we can probably cover enough so you can keep up in a conversation about welding if you ever find yourself in one of those…
All welding processes induce fusion through some energy source; in other words, the base metal is melted in some way. Processes like SMAW use an electrode that melts both induce fusion on the base metal and act as a filler metal for the joint. GTAW, or what you might know by the name of TIG welding, uses a tungsten electrode and an inert gas (helium) to weld the base metal.
What you will find is common between all of the processes mentioned above, is that there is some form of arc or electrode being used to spark the fusion reaction, thus the “A” in all of the acronyms. The only exception in the list above is resistance welding, which uses electric current to generate heat through the resistance of two overlapping metals — simply a slightly different use of electricity to weld.
Arc welding is the most common, but it is important to note that there is also gas welding and energy beam welding. These processes use gas or energy beams to heat up the material, rather than current and voltage. Gas and energy methods, while variant, are fairly simple to understand in basic mechanics.
Each different arc technique uses a different electrode and a different setup of applying flux to the weld. Flux is a purifying agent that helps welds bond materials and maintain uniform structure, therefore increasing strength.
Different welding techniques
For most of the welding techniques, you can somewhat infer how they work from their names. We are engineers, after all, right? Flux-cored arc welding uses a wire with, you guessed it, a flux core.
Contrary to what you may think, submerged arc welding isn’t an underwater process. It uses a consumable electrode to weld under a blanket of flux, therefore submerging the weld under the flux to keep it safe from the atmosphere. Now that we have some background on all of the various welding techniques, we can begin to understand how to weld various metals.
Instead of writing tons of text going into the welding of different metals, here’s a quick guide demonstrating the joining metal along with the processes you can use:
Steel: SMAW, MIG, FCAW, TIG (DC), Resistance
Stainless Steel: SMAW, MIG, FCAW, TIG (DC), Resistance
Aluminum: SMAW, MIG, TIG (AC)
Cast Iron: SMAW
Copper/Brass: TIG (DC)
Magnesium Alloy: TIG (AC)
Titanium: TIG (DC)
As you probably noticed, iron-based metals can be welded with various techniques, but other metals with less compatible cell structures take specific techniques to weld. The reason behind both steel’s wide range of techniques and other metals specific techniques has to do with cell structure, phase changes, melting points, and many other factors.
If you want to join two dissimilar metals, say, aluminum to steel, welders, have to get creative in their techniques. The most common way to weld dissimilar metals, or metals not compatible with each other, is to use a filler metal that is compatible with both. In the case of aluminum and steel, zinc can be used as a transition metal, or special transition inserts can be fabricated.
If you want to learn about the welding of dissimilar metals, these processes are on the cutting edge of materials joining techniques. Groundbreaking research is continually being done in the areas of friction-stir welding, laser welding, and even explosive welding (Google it, you won’t be sorry).
Welding is both an incredibly simple thing to grasp, yet also a process filled with endless complexities and sciences. Whether you use it on a daily basis or not at all, welding has aspects of almost every engineering discipline, and can surely captivate even the dullest of engineers.
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