The magnetic properties of aluminum-nickel-cobalt vary minimally with temperature, and they are still widely used in permanent magnet devices requiring high temperature stability, such as instruments and motors. They are particularly suitable for applications in weapons systems like torpedoes, missiles, and aircraft, as well as spacecraft such as satellites. These materials have a high residual flux density, up to 1.3.5 T, but their intrinsic coercivity is very low, typically less than 160 kA/m. Their demagnetization curve exhibits nonlinear behavior, and the recovery line of aluminum-nickel-cobalt permanent magnets does not coincide with the demagnetization curve. Therefore, special attention must be paid to their unique characteristics during the design and manufacturing of magnetic circuits; stable magnetization treatment is required for the permanent magnets beforehand. Due to the low coercivity of aluminum-nickel-cobalt permanent magnets, it is strictly prohibited to expose them to any ferromagnetic materials during use to prevent local irreversible demagnetization or distortion in the flux density distribution. Additionally, to enhance their demagnetization resistance, the pole surfaces of aluminum-nickel-cobalt permanent magnets are often designed as long cylinders or rods. Furthermore, these materials have low mechanical strength, high hardness, and are brittle, with poor machinability. As a result, they cannot be used as structural components; only limited grinding or electrical discharge machining can be performed during processing, and forging or other mechanical processing methods are not applicable.
Aluminum-nickel-cobalt permanent magnet materials are one of the first permanent magnet materials widely used, and their production processes and technologies are quite mature. The table below lists the common grades of aluminum-nickel-cobalt permanent magnet materials produced in China.
Table: Alnico permanent magnet material grades
|
Code Number
|
Br
(T)
|
HcB
(kA/m)
|
(BH)max
(kJ/m3)
|
αBr
(%/℃)
|
Μr
|
|
LN10
|
0.60
|
36
|
10
|
-0.022
|
6.0~7.0
|
|
LNG13
|
0.68
|
48
|
13
|
6.0~6.7
|
|
LNG32
|
1.20
|
44
|
32
|
-0.016
|
3.5~4.8
|
|
LNG3X2H
|
1.10
|
56
|
32
|
3.2~4.5
|
|
LNGT32
|
0.80
|
100
|
32
|
-0.020
|
2.4~3.6
|
|
LNGT40
|
0.72
|
410
|
40
|
|
LNG52DIV>
|
1.30
|
56
|
52
|
-0.016
|
2.4~3.6
|
|
LNG60
|
1.35
|
60
|
60
|
2.4~3.6
|
|
LNGT56
|
0.95
|
104
|
56
|
-0.02 ~ -0.025
|
2.4~3.6
|
|
LNGT70
|
>0.90
|
145
|
70
|
|
LNGT72
|
1.05
|
111
|
72
|
0.02 ~ -0.025
|
2.0~3.2
|
|
LNGT85
|
1.8
|
120
|
85
|
2.0~3.0
|
|
LNGS9
|
0.5
|
35
|
<9
|
6.0~6.7
|
|
LNGS25
|
1.05
|
46
|
2_5
|
3.2~4.3
|
|
LNGTS28
|
0.7
|
95
|
28
|
Note: L stands for aluminum, N stands for nickel, G stands for cobalt, T stands for titanium, S stands for sintering
The notable feature of aluminum-nickel-cobalt permanent magnet materials is:
① The temperature coefficient is small, and the remanent magnetization reversible temperature coefficientαBrOnly -0.02%/℃ approximately, the remanent force reversible temperature coefficient is +0.015%/℃ approximately;
② Excellent corrosion resistance
③ The Curie temperature reaches 860 °C, and the applicable temperature can reach 550 °C.
