Soft magnetic composites were industrialized in the 1980s. Due to their structure featuring fine and uniform air gaps, these materials experience minimal magnetic field leakage during inductance use, which results in good electromagnetic compatibility for inductive components and reduces eddy current losses caused by leakage magnetic fields. As a result, they have found widespread application.
Meaning of Soft Magnetic Composites
Soft magnetic composites, also known as magnetic powder cores, are a new type of magnetic material made from soft magnetic metals that undergo powdering, insulation treatment, binding, pressing, and heat treatment. They possess advantages such as magnetic isotropy, high magnetic permeability, low coercivity, high Curie temperature, and low losses. They are acclaimed as the “fourth generation” of soft magnetic materials.
Soft magnetic composites combine the advantages of metal and ferrite soft magnetic materials, significantly improving their resistivity compared to soft magnetic metals. This effectively reduces eddy current losses and provides higher saturation magnetization than soft magnetic ferrites, thus meeting the miniaturization and integration requirements of power electronic devices.
These materials can be pressed into various complex shapes, such as rings, E shapes, and U shapes, enabling integrated production of components. Consequently, soft magnetic composites have become the fastest-growing magnetic materials in development and application, used in the production of various inductors, filters, choke coils, and transformers, which are key components in power electronics. They are widely applied in energy, information, transportation, and national defense fields, serving as critical foundational materials for national economic and defense construction.
Classification of Soft Magnetic Composites
According to differences in composition and performance, soft magnetic composites can be categorized into alloy magnetic powder cores and iron powder cores.
Alloy Powder Cores / Alloy Soft Magnetic Composites
Alloy magnetic powder cores are soft magnetic materials made from iron-based alloy powders that undergo surface insulation coating and mixing with inorganic binders, followed by pressing and high-temperature treatment. Based on the different alloy compositions, there are mainly five categories: iron-silicon-aluminum magnetic powder cores (Sendust Cores), silicon-iron magnetic powder cores (Si-Fe Cores), iron-silicon-nickel magnetic powder cores (Neu Flux Cores), high-flux iron-nickel magnetic powder cores (High Flux Cores), and iron-nickel-molybdenum magnetic powder cores (MPP Cores).
Iron Powder Cores / Iron Soft Magnetic Composites
Iron powder cores are soft magnetic materials made from high-purity reduced iron powder or base iron powder that have undergone surface insulation coating and binding agent mixing and pressing. They exhibit good DC superposition characteristics. Their production process is simple, and they are the most economical among various metal magnetic powder cores. Currently, they are the most widely used and consumed type among all metal magnetic powder cores.
Advantages of Soft Magnetic Composites
| Soft magnetic composites have a high saturation magnetic flux density, significantly surpassing that of ferrite soft magnets, which is practically significant for achieving high capacity and miniaturization in electronic components.
| The overall resistivity of soft magnetic composites is increased during manufacturing, reducing eddy current losses caused by leakage magnetic fields.
| They exhibit good stability in magnetic performance, including frequency characteristics, temperature stability, and time stability.
| Soft magnetic composite materials demonstrate good stability in DC bias fields, a benefit that arises from the simultaneous occurrence of high saturation magnetic flux density and low losses.
These materials possess controllable performance. By controlling and varying the conditions of the production process, it is possible to obtain metal soft magnetic powder core materials that satisfy various special usage scenarios and possess unique properties, thus maximizing the fulfillment of specific requirements for special occasions. This is of great practical significance for improving the performance of various electronic products and enhancing product quality.
Soft Magnetic Composites Vs. Silicon Steel
| SMC (Somaloy®) | Silicon Steel | |
|---|---|---|
| Forming Capability | Supports three-dimensional near-net forming, waste rate ≤ 5% | Limited to two-dimensional stamping, waste rate ≥ 15% |
| High-frequency Loss | Eddy current loss will be reduced by 20%-30% (above 1kHz) | Significant eddy current loss |
| Carbon Footprint | 0.83 kg CO2eq/kg (Somaloy 5P) | Typical value 2.5-3.0 kg CO2eq/kg |
| Mechanical Strength | 80-120 MPa | 200-300 MPa |
Method for Preparing Soft Magnetic Powder
In the preparation of soft magnetic composites, the selected magnetic powder particle size is generally less than 100 μm, or even smaller. To achieve high magnetic permeability, a particle size distribution is also necessary. The primary methods for preparing metal magnetic powder include mechanical grinding and atomization.
Mechanical Grinding Method
This method mainly involves producing metal magnetic powder through a ball milling process. In a high-speed rotating ball mill, hard metal balls continuously impact, collide, mix, and grind the raw materials, ultimately crushing the alloy into micron-sized metal magnetic powder.
The ball milling process is simple and cost-effective, making it the most commonly used powder preparation method for soft magnetic composites, which can be divided into wet milling and dry milling. The wet milling process typically involves adding deionized water or anhydrous ethanol as a liquid milling medium into the ball mill container. During milling, the milling medium isolates the magnetic powder from the air, preventing oxidation of the magnetic powder, and making it suitable for easily oxidizable soft magnetic alloys.
Atomization Method
This method involves directly breaking liquid metal into droplets with diameters less than 150 μm, which then condense to form a metal magnetic powder. Atomization includes two types: water atomization and gas atomization.
| Gas atomization: Gas atomization usually employs inert gases such as argon and helium as the atomizing medium, which effectively reduces the oxygen content and minimizes alloy oxidation. The gas as an atomizing medium cools the metal droplets at a slower rate, allowing them to gradually shrink into spherical shapes instead of immediate solidification. Therefore, gas atomization is conducive to producing spherical metal magnetic powder.
| Water atomization: Water atomization, on the other hand, uses water as a cooling medium, resulting in a faster cooling rate compared to gas atomization. However, due to the oxidation issues of alloys during the water atomization process, this method is only suitable for alloys with relatively stable compositions. The equipment and process for atomization are more complex, involve higher production costs, and yield lower quantities of metal magnetic powder.
Applications of Soft Magnetic Composites
| Axial Flux Motors: Soft magnetic composites possess good machinability and can be formed in three dimensions, which enhances the material utilization rate in axial flux motors.
They also have higher power density, making axial flux motors lighter, more compact, and easier to integrate into systems.
Additionally, soft magnetic composites in axial flux motors feature high torque and high power density characteristics, reducing high-frequency losses.
Somaloy is ideal for axial flux motors due to its support for 3D magnetic flux, enabling compact, integrated designs. Its high resistivity reduces eddy current losses at high frequencies, and it offers better thermal uniformity than laminated steel. While its saturation is slightly lower, the gains in efficiency and design flexibility often outweigh that. Today, many motor design software tools include various Somaloy grades for easy simulation and optimization.
| Photovoltaic Inverters: String inverters are mainly used in distributed photovoltaic generation. These inverters operate at high switching frequencies, requiring soft magnetic materials to have low-loss characteristics. The low power loss of soft magnetic composites is particularly suitable for string inverters.
| Charging Stations: Charging stations, onboard chargers (AC/DC), and onboard DC-DC converters are three primary application areas for soft magnetic materials in new-energy vehicles. PFC inductors made from metal soft magnetic powder cores and ferrite powder cores are widely used in charging stations, serving to store energy and filter signals.
Neodymium Magnets and Soft Magnetic Composites Provider
At Tengye, We provide both neodymium iron boron magnets and soft magnetic composites, and we can also supply customized soft magnetic composites according to customer needs.
We made some Somaloy® 700HR-5P for an axial flux motor prototype.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: Bomatec & Gtbcomponents & Linkedin & Gtbcomponents & Mdpi & Sumitomoelectric
