Quick answer: a soft magnetic alloy is selected for easy magnetization and demagnetization, low coercivity and controlled magnetic loss. The best grade is not determined by permeability alone: saturation induction, frequency, part geometry, final annealing condition and the required test method must be specified together.
What Makes an Alloy “Soft Magnetic”?
Soft magnetic materials respond strongly to an applied magnetic field but retain relatively little magnetization after the field is removed. Their narrow hysteresis loop helps reduce energy loss in components that are repeatedly magnetized. Typical engineering indicators include coercivity, initial and maximum permeability, saturation induction, remanence, core loss and electrical resistivity.
These values are affected by alloy family, grain structure, residual stress, thickness, surface condition and test frequency. Forming, machining or welding can introduce stress and reduce magnetic performance, which is why a final magnetic anneal may be part of the component manufacturing route.
Main Soft Magnetic Alloy Families
| Alloy family | Selection strength | Typical decision question |
|---|---|---|
| Nickel-iron | High permeability and low coercivity | Is low-field sensitivity more important than high saturation? |
| Iron-cobalt | High saturation induction | Must the component carry high magnetic flux in limited space? |
| Iron-silicon / electrical steel | Balanced cost, resistivity and core-loss control | What frequency, lamination thickness and loss limit apply? |
How to Select a Soft Magnetic Alloy
1. Define the magnetic duty
State whether the priority is maximum permeability, low coercivity, high saturation, low AC core loss or a controlled hysteresis-loop shape. Include the operating field, frequency and temperature.
2. Specify the product form and final geometry
Strip thickness, bar diameter, part section and magnetic path influence performance. Thin laminations can reduce eddy-current loss in AC service, while solid bar may suit machined pole pieces or shielding components.
3. Control the processing condition
Cold work and machining stress can change coercivity and permeability. The RFQ should identify whether the material is required in a mill-annealed condition or whether the finished component will receive a specified magnetic anneal.
4. Define how properties will be verified
List the magnetic property, test method, specimen orientation, frequency, field strength and acceptance limit. Do not compare supplier data measured under different test conditions as if the values were directly interchangeable.
RFQ Checklist
- Alloy designation or required magnetic-property envelope
- Strip, sheet, bar, wire or finished component geometry
- Dimensions, tolerances, surface condition and quantity
- Required delivery and final annealing condition
- Magnetic test method, orientation, frequency and limits
- Mechanical, chemical, dimensional and documentation requirements
Request a Material Review
Send the application, magnetic targets, product form, dimensions and inspection requirements. SASAALLOY can review the requested material form and identify the information needed for a quotation; availability and final properties must be confirmed against the order specification.
Technical reference: Carpenter Technology, Leadership in Soft Magnetics.
Post time: Nov-20-2018