Permalloy commonly refers to iron-nickel alloys, with nickel content ranging from 30% to 90%. It is a widely used soft magnetic alloy. Through appropriate processing, the magnetic properties can be effectively controlled, such as an initial permeability exceeding 105 and a relative permeability exceeding 106. High permeability, coercivity as low as 2‰ Oersted, and a rectangular coefficient close to 1 or 0, permalloy with a face-centered cubic crystal structure boasts excellent plasticity, capable of being processed into ultra-thin 1μm strips and various forms for use. Common alloys include 1J50, 1J79, 1J85, etc.
The saturation magnetic induction of 1J50 is slightly lower than silicon steel, but its permeability is several tens higher and the iron loss is 2~3 times lower than that of silicon steel. It is suitable for manufacturing transformers with higher frequencies (400~8000Hz), which have small no-load currents and are ideal for small, high-frequency transformers under 100W. 1J79 offers excellent comprehensive performance and is suitable for high-frequency, low-voltage transformers, leakage protection switch cores, common-mode inductance cores, and current transformer cores. The initial permeability of 1J85 can exceed one hundred thousand (105), making it suitable for weak-signal low-frequency or high-frequency input/output transformers, common-mode inductors, and high-precision current transformers.
Nickel-iron permalloys are classified by composition into four main categories: 35%-40% Ni-Fe, 45%-50% Ni-Fe, 50%-65% Ni-Fe, and 70%-81% Ni-Fe alloys. Each type can be manufactured into materials with circular hysteresis loops, rectangular hysteresis loops, or flat hysteresis loops.
35%～40%
Within the 35% to 40% nickel content range, the magnetic anisotropy K1 decreases with increasing nickel content, and the squareness ratio Br/Bs also diminishes, indicating a circular hysteresis loop. This circular loop, combined with high resistivity (at 40% nickel content, ρ=60μΩ·cm; at 48%, ρ=45μΩ·cm) and fine-grained isotropic microstructure, results in lower core losses. For instance, a 0.05mm thick 40% Ni-Fe alloy strip has a loss of 9 watts per kilogram at 0.1T and 20kHz; while the corresponding loss for a 48% Ni-Fe alloy strip is 14 watts per kilogram. This type of alloy is suitable for square wave transformers, DC converters, and more.
45%～50%
Alloys within this composition range possess properties similar to permalloys. High saturation magnetization intensity, with K1 > 0, easy magnetization direction is <100>. Rectangular hysteresis loops can be obtained by forming cubic texture, suitable for magnetic amplifiers, chokes, and transformers. Circular hysteresis loops can also be achieved by forming {210} texture through secondary recrystallization, or by forming fine-grained isotropic microstructure through primary recrystallization. This alloy boasts high permeability and low coercivity, and is suitable for current transformers, grounding fault circuit breakers, micro-motors, and relays, etc.
50%～65%
Alloys within this composition range High Curie temperature, high saturation magnetization intensity, and an ordered state with K1≈0, thus the magnetic field heat treatment effect is particularly pronounced, capable of producing strong induced magnetic anisotropy. At low temperatures (below the Curie point at about 130℃), the hysteresis loop during magnetic field heat treatment is rectangular, DC High permeability, but poor dynamic characteristics; the squareness ratio of the hysteresis loop decreases during magnetic heat treatment at high temperatures (below the Curie point, about 60℃); DC High permeability is not high, but the dynamic characteristics are good. Nickel-iron alloy containing about 55% nickel (with 2% molybdenum) is heat-treated at high temperatures to form {210}<001> texture or fine-grained secondary recrystallization structure, followed by high-temperature longitudinal magnetic field heat treatment, which can significantly improve μi and μm. Nickel-iron alloy with 65% nickel and a fine-grained isotropic microstructure, when subjected to longitudinal magnetic field heat treatment, yields materials with good dynamic properties and rectangular hysteresis loops, suitable for magnetic amplifiers. This alloy, when heat-treated with a transverse magnetic field, produces low Br flat loops; its permeability varies little within a certain magnetic field strength range, and is known as a constant permeability alloy, suitable for inductive components.
70%～81%
The permalloy within this composition range possesses High permeability. Although K1 and λ in binary nickel-iron alloys cannot both drop to zero simultaneously, by adding appropriate alloying elements such as molybdenum, chromium, and copper within this composition range and controlling the cooling rate of heat treatment, K1 and λ can both approach zero, resulting in high permeability and low coercivity. Generally, the μi of such alloys can reach 40 to 60 mH/m. In 1947, Americans R.M. Bozorth and others used purer raw materials, vacuum melted and Finally, after annealing at high temperatures of 1200-1300°C in pure hydrogen, a Ni79Mo5 alloy with extremely high μi and μm values, known as Superalloy, was obtained. Its μi can reach above 150 mH/m, and μm can reach up to 1130 mH/m.
Basic Features
permalloy
Highly permeable iron-nickel soft magnetic alloy under weak magnetic fields.
Nickel Alloys
PM alloy
To enhance resistivity and improve process performance, elements such as Mo, Cr, and Cu are often added to Fe-Ni binary alloys. Besides Fe-Ni alloy systems, other types of permalloys include Fe-Si-Al alloys and amorphous cobalt-based alloys.
The soft magnetic properties of permalloy are excellent, with an initial magnetic permeability μi ranging from 37.5 to 125 mH/m. High permeability μm up to 125~375 mH/m, coercive force Hc of 0.8 A/m, resistivity ρ of 60~85 μΩ·cm.
Alloys are melted in a vacuum induction furnace and then processed into cold-rolled strip, cold-drawn wire, or hot-rolled (forged) sheets and bars through thermal and cold plastic deformation.
Used for manufacturing audio transformers, inductors, magnetic amplifiers, magnetic modulators, chokes, and audio magnetic heads.
