Alnico Magnets

Alnico magnets as they are known consist of alloys: Al (aluminum) Ni (nickel) Co (cobalt), hence Al-ni-co, with additional alloys, iron, copper and titanium and other elements to enhance heat treatment in magnetic properties. They were developed in late 1930’s and commercially available in the early 1940’s. Some of the trade name alloys are: Alcomax, Alni, Arnox, Columax, Hycomax, and Lodex.

alnico magnetsTo produce Alnico magnets conventional methods are used: casting in resin bonded molds and a sintering process. Each process produces Isotropic and Anisotropic magnets. Isotropic Alnico magnets are produced with no orientation and without exposure to electromagnetic field and can be magnetized in any direction. On the other hand, the Anisotropic Alnico magnet castings are heated above their Curie temperature, and then cooled at a controlled temperature rate with an electromagnetic field applied in a specific direction to achieve the desired improved properties.

Anisotropic Alnico magnets can only be magnetized in the direction of orientation.

Sintered MagnetSintered Alnico magnets are produced using a powder metallurgy process and compacted into forming dies. The formed shapes are sintered at high temperature under hydrogen atmosphere. To optimize greater mechanical and magnetic properties heat treatment is used. In the final process, annealing is introduced which enhances magnetic properties, stabilizes the alloy structure and reduces the brittleness. With high operating temperatures of 1020 ⁰F/ 550⁰C alnico magnets are well suited for many applications especially when temperature is a critical point of operation. Alnico magnets are excellent choices for applications involving, high-speed switching and motion, vibration, shock, corrosion resistance, high mechanical properties and relatively low cost.

Typical Magnetic Properties of Alnico Magnets
Isotropic Cast Alnico
Alnico
Grade
Max Energy BHmax
Residual Induction Br
Coercive Force Hc
Intrinsic Coercive Force Hci
Operating Temp Max
Density
MGOe
kJ/m3
kGs
mT
Oe
kA/m
Oe
kA/m
°F
°C
lbs/in3
g/cm3
2
1.65
13.1
7.2
0.72
560
45
580
46
840
450
0.250
6.9
3
1.35
10.7
7.0
0.70
480
38
500
40
840
450
0.249
6.9
7
2.20
18.0
5.8
0.58
1130
90
1250
102
840
450
0.263
7.3
Anisotropic Cast Alnico
5
5.5
43.8
12.8
1.28
640
51
640
51
975
525
0.264
7.3
5DG
6.5
57.7
13.3
1.33
670
53
670
53
975
525
0.264
7.3
5-7
7.5
59.7
13.5
1.35
740
59
740
59
975
525
0.264
7.3
6
3.8
30.2
10.3
1.03
760
61
790
63
975
525
0.265
7.3
8
5.3
42.2
8.1
0.81
1640
130
1850
147
1020
550
0.262
7.3
8HC
5.0
39.8
7.2
0.72
1900
151
2170
173
1020
550
0.262
7.3
9
9.0
71.6
10.6
1.06
1500
119
1500
119
1020
550
0.262
7.3
Anisotropic Sintered Alnico
5
3.9
31.0
10.9
1.09
620
49
630
50
1020
550
0.250
6.9
6
2.9
23.1
9.4
0.94
790
63
820
65
975
525
0.250
6.9
8
4.0
31.8
7.4
0.74
1500
119
1690
134
1020
550
0.253
7.0
8HC
4.5
35.8
6.7
0.67
1800
143
2020
161
1020
550
0.253
7.0
12
5.4
39/43
8.6
0.86
1540
123
1600
127
1020
550
0.260
7.2
15
6.03
44/48
8.8
0.88
1980
160
2050
163
1020
550
0.260
7.2

Unit Conversion: 1 mT=10 Gs, 1 kA/m=4Π Oe, 1kJ/m³=4Π x 10⁻²MGOe

Typical Mechanical & Thermal Properties of Alnico Materials
 
Grade Cast
Coefficient of Thermal Exp. 10⁻⁶ per C
Electrical Resistivity Ohm-cm x 10⁻⁶ at 20⁰C
Transverse Modulus of Rupture
Tensile Strength
Hardness Rockwell C
psi
Pa x 106
psi
Pa x 106
Alnico 2
12.4
65
7,000
48
3,000
21
45
Alnico 3
13.0
60
23,000
158
12,000
83
45
Alnico 5
11.4
47
10,500
72
5,400
37
50
Alnico 8
11.0
53
30,000
207
10,000
69
55

Note: Alnico magnets are inherently brittle, lock ductility; they should not be used for any structural components in design. *All of the data shown above is compiled from industries and research sources and only should be use for reference only.

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