1. Silicon steel

Silicon steel is an alloy. The iron-silicon alloy formed by adding a small amount of silicon (generally less than 4.5%) to pure iron is called silicon steel. This type of iron core has the highest saturation magnetic induction value of 20000 Gauss; Good magnetoelectric performance, easy mass production, low price, low mechanical stress and other advantages, have been widely used in the power electronics industry, such as power transformers, distribution transformers, current transformers and other iron cores.

Silicon steel is the material with the largest output and usage among soft magnetic materials. It is also the material with the largest amount of magnetic materials used in power transformers. Especially suitable for low frequency and high power. Commonly used are cold-rolled silicon steel sheet DG3, cold-rolled non-oriented electrical steel strip DW, cold-rolled oriented electrical steel strip DQ, suitable for medium and small power low-frequency transformers, chokes, and reactors in various electronic systems and household appliances , Inductor core, this kind of alloy has good toughness and can be processed by punching and cutting. The core has laminated and winding types. However, the loss increases sharply at high frequencies, and the general use frequency does not exceed 400 Hz.

From an application point of view, the choice of silicon steel should consider two factors: magnetism and cost. For small motors, reactors and relays, pure iron or low-silicon steel sheets can be selected; for large motors, high-silicon hot-rolled silicon steel sheets, single-oriented or non-oriented cold-rolled silicon steel sheets can be selected; single-oriented cold-rolled silicon steel sheets are often used for transformers sheet. When used under power frequency, the thickness of the commonly used strip is 0.2~0.35 mm; when used under 400Hz, the thickness of 0.1 mm is usually selected. The thinner the thickness, the higher the price.

2. Permalloy

Permalloy often refers to iron-nickel alloys with a nickel content in the range of 30 to 90%. It is a very widely used soft magnetic alloy. Through appropriate technology, magnetic properties can be effectively controlled, such as initial permeability exceeding one hundred thousand, maximum permeability exceeding one million, coercivity as low as two thousandths of Oersted, close to 1 or close to With zero rectangular coefficient, permalloy with a face-centered cubic crystal structure has good plasticity, and can be processed into 1 micron ultra-thin ribbons and various forms of use. Commonly used permalloys are 1J50, 1J79, 1J85 and so on.

The saturation magnetic induction of 1J50 is slightly lower than that of silicon steel, but its magnetic permeability is dozens of times higher than that of silicon steel, and its iron loss is also 2 to 3 times lower than that of silicon steel. It is made into a transformer with a higher frequency (400~8000Hz), and the no-load current is small. It is suitable for making small high-frequency transformers below 100W.

1J79 has good comprehensive performance and is suitable for high frequency and low voltage transformers, leakage protection switch cores, common mode inductor cores and current transformer cores.

The initial permeability of 1J85 can reach more than 100,000, which is suitable for low-frequency or high-frequency input and output transformers, common mode inductors and high-precision current transformers with weak signals.

3. Amorphous alloy

Both silicon steel and permalloy soft magnetic materials are crystalline materials. The atoms are regularly arranged in three-dimensional space to form a periodic lattice structure. There are grains, grain boundaries, dislocations, interstitial atoms, magnetocrystalline anisotropy, etc. Defects are not good for soft magnetic properties. From the perspective of magnetic physics, the irregular arrangement of atoms, the absence of periodicity and the amorphous structure of grain boundaries are ideal for obtaining excellent soft magnetic properties.

Amorphous metals and alloys are a new material field that came out in the 1970s. Its preparation technology is completely different from the traditional method, but adopts the super rapid solidification technology with a cooling rate of about 1 million degrees per second. From the molten steel to the finished strip, it is formed at one time, which is better than the general cold-rolled metal strip manufacturing process Many intermediate processes are reduced. This new process is called a revolution to traditional metallurgical processes. Due to super-rapid solidification, the atoms cannot be ordered and crystallized when the alloy is solidified. The obtained solid alloy has a long-range disordered structure without the crystal grains and grain boundaries of the crystalline alloy. It is called an amorphous alloy and is called a metallurgical material. A revolution in learning.

This amorphous alloy has many unique properties, such as excellent magnetic properties, corrosion resistance, wear resistance, high strength, hardness and toughness, high electrical resistivity and electromechanical coupling properties. Due to its excellent performance and simple process, it has become the focus of research and development in materials science at home and abroad since the 1980s. At present, the United States, Japan, and Germany have complete production scales, and a large number of amorphous alloy products have gradually replaced silicon steel, permalloy and ferrite to the market.

Commonly used types of amorphous alloys are: iron-based, iron-nickel-based, cobalt-based amorphous alloys and iron-based nanocrystalline alloys.

3.1 Fe-based amorphous alloy 

The iron-based amorphous alloy is composed of 80% Fe and 20% Si, B type metal elements. It has high saturation magnetic induction intensity (1.54T), the loss of iron-based amorphous alloy and silicon steel is compared, the magnetic permeability, excitation current All aspects such as iron loss and iron loss are superior to the characteristics of silicon steel sheet, especially low iron loss (1/3-1/5 of oriented silicon steel sheet), replacing silicon steel as a distribution transformer can save 60-70% energy. The strip thickness of the iron-based amorphous alloy is about 0.03 mm. It is widely used in distribution transformers, high-power switching power supplies, pulse transformers, magnetic amplifiers, intermediate frequency transformers and inverter cores, and is suitable for use at frequencies below 10kHz.

3.2 Fe-Ni based-amorphous alloy

The iron-nickel-based amorphous alloy is composed of 40% Ni, 40% Fe and 20% Si, B type metal elements. It has a medium saturation magnetic induction intensity (0.8T), a high initial permeability and a high maximum Magnetic permeability and high mechanical strength and excellent toughness. It has low iron loss at medium and low frequencies. The heat treatment in air will not oxidize, and a good rectangular loop can be obtained after magnetic field annealing. The price is 30-50% cheaper than 1J79. The application range of iron-nickel-based amorphous alloy corresponds to that of medium-nickel permalloy, but its iron loss and high mechanical strength are far superior to crystalline alloys; it is widely used in leakage switches, precision current transformer cores, magnetic shields, etc. Fe-Ni-based amorphous alloys are the earliest developed in China and are currently the most widely used amorphous variety among domestic amorphous alloys, with an annual output of about 200 tons. The iron oxide nickel-based amorphous alloy (1K503) does not occur in the air heat treatment and has obtained the national invention patent and the US patent.

3.3 Cobalt-based amorphous alloy

Cobalt-based amorphous alloy is composed of 80% Co and 20% Si, B type metal elements. It has the highest magnetic permeability among all amorphous alloys, and has lower saturation magnetic induction, low coercivity, and low coercivity. Loss, excellent wear resistance and corrosion resistance, good temperature stability and aging stability, shock and vibration resistance. Generally used in demanding military power supplies such as transformers and inductors to replace permalloy and ferrite, but the price is high.

4. Microcrystalline (Nanocrystalline) Alloy（Nanocrystalline alloy）

Nanocrystalline special amorphous alloy, iron-based nanocrystalline alloy is an amorphous material formed by the rapid solidification process by adding a small amount of Nb, Cu, Si, and B elements as the main element of iron. After heat treatment, this kind of amorphous material can obtain microcrystals with a diameter of 10-20 nanometers, which are dispersed on the amorphous matrix and are called microcrystals, nanocrystalline materials or nanocrystalline materials.

Nanocrystalline materials have excellent comprehensive magnetic properties: high saturation magnetic induction (1.2T), high initial permeability (80,000), low Hc (0.32A/M), low high-frequency loss under high magnetic induction (P0. 5T／20kHz＝30 W/kg), the resistivity is 80 micro ohm cm, which is higher than permalloy (50-60 micro ohm cm). After longitudinal or transverse magnetic field treatment, high Br (0.9) or low Br value can be obtained (1000Gs).

Nanocrystalline is currently the material with the best comprehensive performance on the market; applicable frequency range: 50Hz-100kHz, best frequency range: 20kHz-50kHz. It is widely used in high-power switching power supplies, inverter power supplies, magnetic amplifiers, high-frequency transformers, high-frequency converters, high-frequency choke cores, current transformer cores, leakage protection switches, and common-mode inductor cores.