Composite metal foam (CMF) is a foam formed by hollow metal balls made of materials such as stainless steel or titanium embedded in a metal matrix made of steel, titanium, aluminum or other metal alloys. This material is lightweight and strong and can be used in areas such as aircraft wings, vehicle armor and human body armor. In addition, CMF has better thermal insulation properties compared to traditional metals and alloys such as steel. The combination of weight, strength and thermal insulation properties means that CMF is also expected to be used to store and transport nuclear materials, hazardous materials, explosives and other heat-sensitive materials. But to realize these applications, manufacturers need to weld multiple CMF parts together. Traditional welding technology will melt the bubbles, making CMF more ideal.

Researchers have now demonstrated that an induction welding technique that relies on electromagnetic fields can weld CMF without damaging the air bubbles in the foam. This illustration shows how it works. Note that CMF is cool enough to be touched by hand, just a few inches away from the soldering point. Source: Afsaneh Rabiei, North Carolina State University

Researchers at North Carolina State University have discovered a new method of welding composite metal foam (CMF) that maintains its lightweight, strong and thermally insulating properties, which are critical for many applications.

Researchers at North Carolina State University have now found a welding technique that can be used to join composite metal foam (CMF) parts together without compromising the properties that make CMF an ideal material. CMF is lightweight, strong and effectively insulates high temperatures, so it is expected to be widely used in various fields.

CMF is a foam that consists of hollow metal spheres made of materials such as stainless steel or titanium embedded in a metal matrix made of steel, titanium, aluminum or other metal alloys. This material is lightweight and strong and can be used in areas such as aircraft wings, vehicle armor and human body armor.

In addition, CMF has better thermal insulation properties compared to traditional metals and alloys such as steel. The combination of weight, strength and thermal insulation properties means that CMF is also expected to be used to store and transport nuclear materials, hazardous materials, explosives and other heat-sensitive materials.

However, to achieve these applications, manufacturers need to weld multiple CMF parts together. This brings up a problem. "Traditional fusion welding uses a filler to join two pieces of metal," said Afsaneh Rabiei, corresponding author of the new research paper and a professor in the Department of Mechanical and Aerospace Engineering at North Carolina State University. "This is problematic because the metal that fuses the two pieces of CMF is solid, so it Lacking the ideal properties of CMF on both sides, any welding method that uses direct heating of the molten metal will cause some of the pores in the CMF to be filled, thus affecting its performance. In short, this means that most forms of conventional welding will not work well with metal foam."

However, researchers have now found a method of welding that works extremely well. Known as induction welding, it uses an induction coil to generate an electromagnetic field that heats the metal to weld it.

"Because CMF is only 30-35% metallic, the electromagnetic field is able to penetrate deep into the material, allowing for a good weld," Rabiei said. "The air pockets that make up the remaining 65-70% of the CMF serve to insulate the material from heat. In this way, induction welding heats the target area where the two pieces of CMF are joined, but prevents heat from spreading outward from the connection. This helps maintain the properties of the CMF."

"This is an important step forward, as the properties of CMF make it attractive in a wide range of applications, but there must be a way to weld CMF parts without compromising the properties that make it attractive."

The paper, titled "Study on Welding of Porous Metals and Metal Foams," was recently published in the journal Advanced Engineering Materials.

Compiled source: ScitechDaily