AlNiCo Magnets: Performance, Applications, and Advantages Explained

AlNiCo (Aluminum Nickel Cobalt) magnets were once the strongest permanent magnets before the rise of rare earth materials in the 1970s. While modern magnets like ferrites and rare earth magnets have since taken over many applications, AlNiCo magnets still hold a critical role in specific industries. Their unique combination of high-temperature stability and magnetic strength makes them irreplaceable in specific high-performance environments.

In this post, we’ll explore the performance, advantages, limitations, and key applications of AlNiCo magnets. Additionally, we’ll take a closer look at the production process behind these remarkable magnets and their continued relevance in today’s industrial landscape.

AlNiCo Magnet Performance and Comparison

To understand where AlNiCo magnets stand in today’s market, it’s essential to compare their properties with other types of permanent magnets. Here’s a performance comparison of various permanent magnets:

Magnet Type	Residual Magnetism (Br/kGs)	Coercivity (Hcj/kOe)	Maximum Energy Product (BHmax/MGOe)	Curie Temperature (Tc/°C)	Maximum Operating Temperature (Tw/°C)
Ferrite	8-14	0.3-0.8	1-7	680	400
AlNiCo	6-13.5	0.5-1.8	1-12	860	550
Soft Ferrite	2-5	1-5	2-5	450	250
SmCo (Samarium Cobalt)	7-11.5	5-25	15-35	850	350
NdFeB (Neodymium-Iron-Boron)	10-15	8-40	20-60	312	200

As the table shows, AlNiCo magnets offer a unique balance between high residual magnetism and high Curie temperature, making them ideal for applications where temperature stability is crucial. Although newer materials like NdFeB and SmCo offer stronger magnetic fields, AlNiCo remains the go-to choice for high-temperature and corrosion-resistant environments.

Key Advantages and Limitations of AlNiCo Magnets

Like any material, AlNiCo magnets come with their own set of pros and cons. Here’s a breakdown of what makes them stand out and where they fall short.

Advantages:

High Residual Magnetism: AlNiCo magnets maintain strong magnetic fields, ensuring long-term stability in demanding applications.
Minimal Temperature Coefficient: With a Curie temperature of up to 860°C, AlNiCo magnets retain their magnetism in high-temperature environments.
Excellent Corrosion Resistance: These magnets resist rust and degradation, which is especially important in industries like aerospace, marine, and high-humidity environments.

Limitations:

Low Mechanical Strength: AlNiCo magnets are more brittle than some other types, which means they require careful handling.
Difficult Machinability: Due to their hardness, shaping and machining AlNiCo magnets can be challenging.
Vulnerability to Demagnetization: AlNiCo magnets have lower coercivity, making them susceptible to losing their magnetic properties if exposed to vibration, shock, or reverse magnetic fields. This calls for specialized design considerations to prevent demagnetization.

Due to the low coercivity of AlNiCo permanent magnet materials, measures are often taken to enhance their resistance to demagnetization. For example:

Magnetic poles are typically designed in elongated cylindrical or rod-like shapes.

Strict control is required over the reverse magnetic field in the operating environment to prevent irreversible demagnetization or distortion in the magnetic flux density distribution.

Applications of AlNiCo Magnets

While AlNiCo magnets are no longer as common in low-cost, high-strength applications, they are still indispensable in certain specialized fields. Some notable applications include:

Aerospace and Military Equipment: AlNiCo’s high temperature and corrosion resistance make it essential for components in aircraft and defense technologies.
High-End Audio Equipment: AlNiCo magnets are used in speakers and microphones, where their stability and corrosion resistance are crucial for sound clarity and longevity.
Automotive and Metrology Instruments: AlNiCo magnets play a vital role in sensors and devices that require precise measurements and high stability.
Electromagnetic Applications: From magnetic chucks to sensors, AlNiCo is used in various electromagnetic devices requiring stable, long-lasting magnetism.

Performance Grades

Commercial AlNiCo grades are generally categorized into levels 2, 3, 4, 5, 6, 8, and 9, primarily distinguished by their magnetic properties and composition. Among these, grades 2, 3, and 4 are isotropic magnetic materials, while the rest are anisotropic magnetic materials.

Theoretically, the maximum energy product of AlNiCo magnets can reach 30–35 MGOe. However, in practice, commercial magnets have achieved only about one-third of this theoretical value. If AlNiCo magnets could reach approximately 80% of their theoretical value, like other permanent magnet materials such as ferrite, samarium cobalt, and neodymium iron boron, they would have even greater application prospects due to their excellent corrosion resistance and temperature stability.

Grade	Br (mT)	Br (Gs)	Hcb (kA/m)	Hcb (Oe)	(BH)max (kJ/m³)	(BH)max (MGOe)	Density (g/cm³)	αBr (% Change Per °C)	αHcj (% Change Per °C)	Tc (°C)	TW (°C)
LN9	680	6800	30	380	9	11.3	6.9	-0.03	0.02	810	450
AlNiCo3	600	6000	40	500	10	12	6.9	-0.03	0.02	810	450
LNG12	720	7200	45	500	12.4	15.5	7	-0.03	-0.02	810	450
LNG13	700	7000	48	600	12.8	16	7	-0.03	0.02	810	450
LN37	1200	12000	48	600	40	4.65	7.3	–	–	–	–
LN40	1250	12500	48	600	40	5	7.3	–	–	–	–
LN44	1250	12500	30	980	9	1.13	6.9	-0.02	–	525	–
AlNiCo5DG	LN52	1300	13000	56	700	52	6.5	7.3	0.02	860	525
AlNiCo5-7	LN60	1350	13500	69	740	60	7.5	7.3	0.02	860	525
AlNiCo6	LNT28	1000	10000	58	720	28	3.5	7.3	-0.02	–	–
AlNiCo9HC	LNT36/	700	7000	140	1750	36	4.5	7.3	-0.025	860	550
LNT18	580	5800	100	1250	18	2.2	7.3	-0.025	0.02	860	550
LNT32	800	8000	100	1250	32	4	7.3	-0.025	0.02	860	550
LNT40	800	8000	110	1380	40	5	7.3	-0.025	0.02	860	550
LNT60	900	9000	110	1380	60	5	7.3	-0.025	0.02	860	550
LNT72	1050	10500	120	1400	72	9	7.3	-0.025	0.02	860	550

AlNiCo Magnet Production Process

AlNiCo magnets are manufactured using two processes: casting and sintering. Among these, cast AlNiCo offers higher performance and is the mainstream choice in the market. However, due to the poor machinability of cast AlNiCo, sintered AlNiCo is preferred for small components, complex shapes, or applications requiring high uniformity.

Casting Process:

Steps: Material Preparation → Melting → Casting → Heat Treatment → Performance Testing → Machining → Inspection → Packaging
Use: Cast AlNiCo magnets offer superior performance and are commonly used in high-precision applications like audio equipment and scientific instruments.
Advantages: High performance with excellent magnetic properties.
Limitations: Poor machinability, making it less suitable for complex or small components.

Sintering Process:

Steps: Material Preparation → Powdering → Pressing → Sintering → Heat Treatment → Performance Testing → Machining → Inspection → Packaging
Use: Sintered AlNiCo magnets are more cost-effective and ideal for smaller, more complex parts, like sensors and electronic components.
Advantages: Better machinability and suitable for high-volume production of intricate parts.
Limitations: Slightly lower performance compared to cast magnets.

Conclusion

While materials like NdFeB and SmCo have gradually replaced AlNiCo magnets in many low-cost, high-strength applications, they remain essential for specific specialized uses due to their exceptional corrosion resistance, high-temperature stability, and magnetic strength. For industries that require reliable performance in demanding environments, AlNiCo magnets continue to offer an irreplaceable solution.

If you’re looking for custom AlNiCo magnets or expert advice on selecting the right magnet for your application, Jinghong can help. With our expertise in high-quality magnet production, we provide tailored solutions to meet your specific needs.

News

Understanding AlNiCo Magnets: Advantages, Applications, and Manufacturing Process