Thursday, March 31, 2022

How Do You Distinguish Between Different Metal Alloys For Welding?

Rolls of metal sheeting in a warehouse

It is important to know what type of metal you are working with before welding. Some metals are weldable, others are not - but knowing the type will help you determine the proper technique and methods needed for successful welding. 

The more you work with metals and the greater experience you have, you may easily come to recognize what is in front of you. Until then, we’ve got some tests to help you distinguish between different metal alloys for welding. 

Common Ways to Test Metal Alloys

There are 7 general tests that can help you distinguish between metal alloys, including: 

  • Visible surface appearance

  • Spark test

  • Chip test

  • Magnetic test

  • Torch test 

  • Chemical test

  • Hardness test

Let’s take a closer look at each. 

Visible surface appearance. Familiarizing yourself with the visible appearance of metal alloys as well as their common applications, you can get an idea for the type of alloy you are working with - or at least narrow it down. 

Spark Test. You can determine the type of metal you are getting ready to weld by determining whether or not there is a spark when holding it against a grinding wheel. If there is, you may be dealing with stainless steel, cast iron, wrought iron, nickel, etc. Otherwise, you won’t find sparks with metals such as bronzes, coppers, brasses, lead, aluminum alloys, and zinc alloys.  

Chip Test. Using a chisel to chip a small piece off of the metal can give you some insight. The size of the chip, whether its edges are smooth or sharp, the grain, and so on can all be important key aspects of identification. For example, copper chips are smooth with sawtooth-like edges. Brass and bronze have the same characteristics. The differing factor is that copper chips in a continuous strip while the latter has smaller, more brittle chips. 

Magnetic Test. Ferrous metals are magnetic, nonferrous metals are not. All you need is a small magnet to perform this test. You will find that steel, nickel, and iron alloys are strongly magnetic. Copper alloys, aluminum alloys, and zinc alloys are not. 

Torch Test. By firing up a torch and heating the metals, welders are able to better distinguish between them. This is done by visibly inspecting the melted metal as well as paying attention to how fast it melted. Each metal will react a little differently to the heat. For instance, brass and bronze melt rapidly and turn red before they do. Brass may give off white flumes. Copper requires a larger flame to melt and its color becomes very pronounced just before it melts. It does so slowly and may tend to bubble if close to the flame. 

Chemical Test. Certain chemicals can be used to determine the metal you are using. Of course, it is important to have an understanding of what you are doing before you attempt these tests. An example is putting a few drops of 45% phosphoric acid onto stainless steel - if it bubbles, then it is stainless steel. There are a few different tests for various metals that you can use. 

Hardness Test. This test can be done in different ways, but it involves pressing a specific object known as the indenter into the surface of the metal. Its hardness can be determined based on the depth of the penetration or the size of the impression. By understanding the hardness of common metals, you can narrow down which one you may be confronting. 

Learn More About Metal Alloys at AtlasBronze

There are quite a few different metals and metal alloys so it can be tough to always know exactly which is which. But, if you are a welder, it is important to know the properties of each of the metals you are using at all times. 

If you are looking for the right metal for your application - or you aren’t sure which one is best - the experienced professionals at AtlasBronze can help. Contact us at (800) 478-0887 or reach out to us online. 

Wednesday, March 30, 2022

Is It Possible To Weld Two Different Metals Together?

A welding torch making sparks

Many different industries and applications join dissimilar materials together for a variety of reasons. Combining dissimilar metals can allow the best properties of each metal to be used. 

At Atlas Bronze, we know that before any welding operation can begin, the welder must be able to identify and understand the characteristics of each material. For these reasons, welding different metals together, requires expert skill and knowledge.

Equipped with that knowledge, whether for brass welding or copper welding, an experienced welder can join even materials that are difficult to weld, skillfully and successfully.

Dissimilar Metal Welding 

Dissimilar metal welding is the welding process that joins different metal alloys. 

To successfully weld these disparate types of material, the welder must understand:

  • Dilution and Alloying -  metals require a solid solution in which the mixture will produce stable metallurgical phases, whether that takes one or more phases. The amount of dilution necessary determines the phase.

  • Level of Weldability - joining dissimilar metals can lead to a high risk of hot or solidification cracking. Weldability measures how metals can be joined without cracking occurring.

  • Electrochemical characteristics -  Corrosion can develop at the part of the joint where the metals transition from one to the other, in what is called the intermetallic zone; or on the overlay surface. The risk of corrosion is highest if metals have significantly different electrochemical properties caused by dilution.

  • Melting point - metals may melt at different temperatures. A pre-heating process will rapidly bring all metals to their melting point, so melting is not required.

  • Thermal expansion coefficient - this expansion refers to the ways in which metals expand, changing size and shape, when heated. Should two metals being welded change shape at different rates or degrees, the weld can strain as it sets, causing thermal cracking.

  • Heat affected zone - if there are heat affected zones immediately adjoining the weld, that weld can display majorly different physical properties from the original base metal. Higher hardness occurs in this way with high carbon or cast iron, leading to reduced strength and brittle fracture.

How Dissimilar Metals are Joined

Traditionally, dissimilar metals are joined through fusion ARC welding to prevent degradation of strength, toughness, and corrosion.

Laser weld overlay can also be used to join these metals. Laser classing of dissimilar materials offers benefits such as: 

  • Less sensitive laser weld overlay to different melt temperatures.

  • Very low dilution

  • Thinner clads

  • Reduced sensitivity to thermal expansion 

  • Control of detrimental metallurgical phases

  • Reduction or elimination of solidification cracking 

  • Higher corrosion resistance in a single thin layer

  • Elimination of multiple layer requirements 

  • Lesser pre-machining

  • Smaller heat affected zone for less distortion

  • High hardenability of materials without preheat

  • Reduction or elimination of preheat requirements 

  • Ability of laser overlay of ductile cast iron without significant preheat

  • Post weld heat treatment eliminated or reduced

  • High quench rates for finer grain structure and higher corrosion potentials

In short, laser is the ultimate heat source tool for the welding/cladding of dissimilar materials.

Are There Any Materials That Can’t Be Welded?

The answer to this question depends on the type of welding method. Fusion welding can’t be used for the welding of:

  • Aluminum and carbon steel

  • Aluminum and copper

  • Aluminum and stainless steel

  • Titanium and steel

However, non-fusion welding, such as diffusion bonding, explosion welding, ultrasonic, and friction welding are very effective for joining these metal combinations as well as other insoluble metals.

Ready to Learn More about Welding Different Types of Metals?

At Atlas Bronze, our skilled experts are here to help. Reach out to us today!