Metal foam: A new metallic material that is both “strong” and “lightweight”.

Metal Foam has a unique structure, combining the characteristics of metal and the functional properties of porous materials. Metal foam belongs to the porous metal materials, the internal porosity can be as high as 90% or more, the shape is like “foam” or “honeycomb”, breaking the traditional concept of dense structure of metal, both metal “strong” characteristics and bubble “light” characteristics, is a new structure-function integration of metal materials. “It breaks the traditional concept of dense structure of metal and has both the characteristics of metal and bubble, which is a new type of metal material with structure-function integration. Due to its unique structure, foam metal not only retains the conductivity, ductility, weldability and other characteristics of the base metal material, but also has the functional properties of porous materials, such as energy absorption and vibration damping, noise reduction, electromagnetic shielding, air permeability and water permeability, which has attracted widespread attention in the field of materials science at home and abroad and is widely used in aerospace and petrochemical fields.

The main ways to categorize metal foam are:
(1) According to the size of pore diameter and porosity: pore diameter less than 0.3mm, porosity between 45% and 90%, known as porous metal; and pore diameter of 0.5-6mm, porosity greater than 90%, known as metal foam;
(2) According to the pore structure: it is divided into through-pore structure and closed-pore structure;
(3) According to the preparation process: initially prepared by foaming method is called metal foam, and later developed a percolation casting and other methods of preparation is also called ventilation metal;
(4) According to the type of matrix: aluminum foam, nickel foam, copper foam and so on. Preparation process, the traditional preparation method to get the metal foam is mostly complex irregular pore structure, and 3D printing can accurately control the pore structure, in terms of precision to empower the metal foam to broaden the application scenarios, such as porous titanium in the medical, precision instruments and other fields to fill the foam metal application gaps.

Structural-functional integrated material, metal foam application prospect is broad
Metal foam integrates structure and function: as a structural material, metal foam has the characteristics of light weight and high specific strength; as a functional material, metal foam has a variety of phySical properties such as porous, vibration damping, damping, sound-absorbing, soundproofing, heat dissipation, shock absorption, electromagnetic shielding and so on. With its unique properties, metal foam has been widely used in industrial fields and high-tech fields:
(1) Utilizing light weight and high specific strength characteristics, it is used to make water flotation devices, sports equipment (such as sledges, etc.), and corresponding parts of aerospace vehicles;
(2) The use of porous, with the production of chemical filters, for the purification of water used in the gasification processor, automatic refueling of oil bearings, scented decorations, etc.;
(3) the use of vibration damping, damping performance, with its production as a buffer, vibration absorber, such as the landing gear of the spaceship, elevator transmission safety cushions and a variety of boxes, especially air transport boxes, machine tool beds, bases, damping rings, and so on;
(4) The use of its electromagnetic shielding, lightweight and excellent sound absorption, sound insulation properties, has been used to make the construction industry's sound insulation panels, electronic instruments shell and electric shielding room structure.

In specific materials, the metal foam is widely used in aluminum, nickel, copper and its alloys, the main characteristics of different matrix materials and application areas vary.
(1) Aluminum foam: As the earliest developed foam metal material, the main advantage of aluminum foam lies in light weight, heat insulation, sound insulation, electromagnetic shielding, absorption of impact energy, etc., which is used in the impact protection layer of missiles, aircraft and their recycled parts, and is also used in the fields of automobile buffer, electronic and mechanical vibration damping device, electromagnetic wave shielding cover of power supply in the pulse, and so on;
(2) Nickel foam: with its connected pore structure and high porosity, nickel foam in the high ventilation, high surface area and capillary force, while in the corrosion resistance has significant advantages, commonly used in the production of fluid filters, catalytic converters, atomizers and battery electrode plates and heat exchangers;
(3) Copper foam: copper foam has good electrical conductivity and ductility, in the preparation of battery negative electrode (carrier) materials, catalyst carriers and electromagnetic shielding materials and other aspects of considerable potential.