Soft magnetic alloys are characterized by high magnetic permeability and low coercivity in weak magnetic fields. They are widely used in the radio electronics industry, precision instruments, remote control, and automatic control systems. Together, they primarily serve in energy conversion and information processing, making them an important material in the national economy.
Definition of Soft Magnetic Alloy Materials
Soft magnetic materials mainly include metal soft magnetic materials, ferrite soft magnetic materials, and other soft magnetic materials. Soft magnetic alloy materials have low coercivity and high magnetic permeability, which can be easily magnetized and demagnetized. Their main functions include guiding magnetism and converting and transmitting electromagnetic energy.
Classification of Soft Magnetic Alloys
There are many types of soft magnetic alloys, which can be classified based on the elements that constitute the alloy, such as electromagnetic pure iron, iron-silicon alloys, iron-nickel alloys, iron-aluminum alloys, iron-silicon-aluminum alloys, and iron-cobalt alloys.
With appropriate processes, the magnetic properties of soft magnetic alloys can be effectively controlled, achieving initial permeabilities over 105, maximum permeabilities over 106, coercivities as low as 2‰ Oersted, and rectangular ratios approaching 1 or 0. Soft magnetic alloys with a face-centered cubic crystal structure exhibit excellent plasticity and can be processed into ultra-thin strips of 1μm thickness in various forms.
Factors Affecting the Performance of Soft Magnetic Alloys
| Chemical Composition: The chemical composition is one of the main factors determining the performance of soft magnetic alloys. For example, good soft magnetic performance is observed in iron-nickel alloys with nickel content ranging from 36% to 83%. Adding certain alloying elements, such as molybdenum, can improve resistivity, reduce sensitivity to stress, and enhance initial permeability, but may decrease saturation magnetization and Curie temperature.
For iron-silicon-aluminum alloys, the relationship between composition and magnetic properties is even more critical, with slight deviations in composition leading to significant declines in magnetic performance. In iron-cobalt alloys, increasing cobalt content raises saturation magnetic induction and Curie temperature, with Bs exceeding 2.4T at 35% Co.
| Impurities: Certain impurity elements can exist in soft magnetic alloys as interstitial or substitutional solid solutions, causing lattice distortion and creating micro-stresses that hinder the free movement of domain walls. Some elements do not dissolve and form compounds of carbon, nitrogen, or oxygen.
These non-magnetic inclusions can pin the domain walls, resulting in increased coercivity and decreased permeability. High-quality soft magnetic alloys require not only pure alloy raw materials with minimal impurities but also often employ vacuum melting and high-temperature heat treatment in pure dry hydrogen or high vacuum to further remove impurities.
| Grain Orientation: In the crystal structure, some directions are easy to magnetize, and others are difficult to magnetize. When magnetized along the easy direction, the magnetic performance is better. Soft magnetic alloys are primarily formed through cold and hot processing. The magnetism of hot-processed materials is generally isotropic, but cold processing can create a cold-rolled texture or crystalline texture, leading to grain orientation. Magnetic performance varies with magnetization direction; iron-nickel and iron-silicon alloys exhibit better magnetic performance along the rolling direction. Thus, magnetization should be conducted along the rolling direction during use.
| Stress: The magnetic performance of soft magnetic alloys is very sensitive to stress. Internal stresses during manufacturing can lead to reduced permeability and increased losses. External forces also influence the magnetic properties of soft magnetic alloys, particularly for high-performance alloys, where the adverse effects can be significant.
Therefore, it is essential to enclose the core in a protective casing. Coupling between external stress and magnetostriction can alter the direction of magnetization, causing stress anisotropy. Different methods of applying force can either improve or worsen the magnetic conductivity of the alloy.
| Temperature: Changes in environmental temperature, as well as temperature variations caused by losses in the core, will affect magnetic performance. As temperature increases, atomic arrangements tend to become more chaotic, leading to reduced spontaneous magnetization intensity. The changes in permeability and coercivity are related to magnetic crystalline anisotropy and magnetostriction coefficients, both of which vary with temperature.
| Thickness of Cold-Rolled Strips: The thickness of cold-rolled soft magnetic alloy strips affects their performance in that eddy current losses, due to the eddy current effect in alternating magnetic fields, are proportional to the square of the thickness. Additionally, due to the skin effect, the thickness of the alloy must be less than a certain value at a specific frequency. Therefore, in practical production, reducing thickness helps lower eddy current losses and improve material utilization. However, reducing thickness may increase abnormal losses and production costs.
Applications of Soft Magnetic Alloys
Soft magnetic alloy materials have developed rapidly in recent years, holding a significant advantage in high-end applications. They are primarily used in transformers, relays, inductors, semiconductor materials, magnetic shielding covers, and electric motor stators and rotors, with substantial room for growth in product application demand.
| Transformers: For instance, distribution transformers using amorphous soft magnetic alloys can reduce iron losses, improve efficiency, and achieve energy conservation. In high-frequency transformers, nanocrystalline soft magnetic alloys exhibit high saturation magnetism and low losses, effectively reducing transformer size and increasing power density.
| Inductors: In circuits such as switching power supplies and inverters, inductors made from soft magnetic alloys can store and convert electrical energy. For example, the high permeability and low loss characteristics of nanocrystalline soft magnetic alloys make them widely used in high-frequency inductors, enhancing the performance and efficiency of inductors.
| Reactors: In power systems, reactors are used to limit short circuit currents and absorb reactive power. Reactors made from amorphous soft magnetic alloys possess advantages such as low losses and high saturation magnetism, improving reactor performance and reliability.
Magnet Manufacturer
At Tengye, we’re thrilled to be early participants in your new projects. Our passion for magnets extends from material selection and design optimization to providing magnetic solutions. We hope to bring our knowledge and experience to the forefront by actively engaging in your upcoming projects. Work with our magnet experts to get the right magnet solution.
Image Source: Ars.els-cdn & Carpenterelectrification & Mdpi & Researchgate
