1. What is metal foam and aluminum foam
In the course of history, the discovery of metal foamed constitutes an important milestone in the revolution of the entire field of materials engineering. Metal foam is a material composed of a metal structure that has a large number of pores and is filled with gas along the structure [2]. The pores of these metal foams can be interconnected or sealed, and are called open-cell foam and closed-cell foam, respectively, as shown in Figure 2(a)(b) [3]. Among them, the aluminum foamed material is currently the most promising foam metal, due to its high porosity, low density, light weight, high strength, good compressibility, strong impact absorption, good sound absorption performance, and good electromagnetic shielding performance. Excellent performance, therefore known as the “metal star” [4], widely used in other processing methods in the fields of aerospace engineering, manufacturing and physical sciences.
Figure 2. Structural characteristics of aluminum foamed: (a) Open-cell aluminum foam; (B) Closed-cell aluminum foam [3]
2. The discovery of aluminum foamed
Throughout history, materials such as bone, wood, and pumice have been widely used for a long time. Many researchers predict that the utility of these materials has promoted the production of man-made materials such as metal foam. Although most of the foaming technologies currently in use have been proposed since the 1950s, studies have shown that the discovery of aluminum foamed can be traced back to 1926, when M.a. De Meller first mentioned metal foaming in a French patent. Meller once suggested that the metal foaming process can be achieved by introducing inert gas into the molten metal, or by using a foaming agent such as carbonate in the molten metal. Although this is just a patent based on the idea, it lays the foundation for the next steps required in the development of aluminum foam. John C. Elliott further developed this idea 20 years later, designing an updated version of the Meller patent and introducing the first available aluminum foam, which in turn contributed to the commercialization of the material in Japan in the 1990s. The release laid the foundation [5].
3. Performance and application of aluminum foamed
Aluminum foamed is a metal with high porosity and porous structure, in which the sealed pores account for about three-quarters of the total volume of the metal material, making the material very light [7]. In addition to the above characteristics, aluminum foamed also has impressive energy absorption characteristics and high compressibility [7]. Regarding the density, the researchers found that the density of most aluminum foamed samples is about 0.4-1.2 g·cm-3 [6]. In addition, aluminum foamed also has sound absorption, recyclability and low thermal conductivity [7].
In terms of application, the electromagnetic shielding, light weight and absorptive properties of aluminum foam make it an ideal candidate for components used in controlled nuclear fusion devices, automobiles, aerospace and construction industries because of its resistance to extreme physical environments. In the controllable nuclear fusion device, closed-cell aluminum foam is an excellent electromagnetic shielding material. Due to the interconnection of the aluminum foam skeleton, it has a huge specific surface area and good ability to absorb and reflect electromagnetic waves. Various losses occur, such as absorption loss, reflection loss, etc., so that foamed aluminum has excellent electromagnetic shielding performance. Moreover, it was also found that the electromagnetic shielding effectiveness of foamed aluminum showed a trend of first decreasing and then increasing with the increase of electromagnetic wave frequency [3]. In the aerospace industry, foamed aluminum is used to make space cones or turbine parts. Due to the low quality of foamed aluminum, it is particularly useful for reducing the total weight of aircraft components [7]. And as an excellent energy-absorbing material, foamed aluminum is used to manufacture spacecraft’s buffers, vibration absorbers and the bottom of the spacecraft’s return cabin, so that the spacecraft can achieve a safe landing and protect the safety of astronauts and space equipment. Through effective energy absorption and shock absorption, foamed aluminum can ensure the safety of astronauts under the impact of the spacecraft landing, as shown in Figure 3 [8].
Figure 3. Improved partial structure of the impact-resistant bilge[8]
1-upper skin; 2-foam aluminum stringers; 3-lower skin
In the automotive industry, foamed aluminum helps reduce the total number of parts used in the frame, makes the assembly process more efficient, and ultimately helps reduce costs and improve performance [7]. At present, foam aluminum is used in anti-collision bars, beams and door beams in automobile body structures on the market, as shown in Figure 4 [9-10].
Figure 4. (a) is a diagram of partial energy absorbing parts of the car body;
(B) Schematic diagram of foam aluminum anti-collision bar
In the construction industry, the main use of foamed aluminum is as a protective, fire-resistant barrier to prevent severe noise. The typical application of closed-cell aluminum foam in architecture is the Shanghai SOHO Fuxing Plaza. The designer uses a large amount of foam aluminum to absorb and insulate sound, as shown in Figure 6 [11].
The discovery of aluminum foamed is considered to be a remarkable achievement. The foamed aluminum material combines excellent electromagnetic shielding performance, light weight, low density, shock absorption and energy absorption performance, so it has very good performance in various industries today. Broad applicability. Interestingly, aluminum foamed is also an environmentally friendly product that can be recycled, which means that it is a sustainable material and is expected to be used in large quantities in future industrial applications.
Post time: Nov-30-2021
