Sintered AlNiCo magnet

Alnico magnets are divided into cast Alnico magnets and sintered Alnico magnets according to the manufacturing process. With the vigorous development of rare earth permanent magnets in recent years, the market share of Alnico has gradually declined, but Alnico still occupies a place in some fields requiring high temperatures because of its unique physical properties. Sintered Alnico magnets use a powder metallurgy process, and The qualified rate of sintered Alnico magnets can reach more than 95%. Because of the fine grain and no casting defects, compared with cast Alnico materials, sintered Alnico magnets have high mechanical properties and are suitable for environments with high vibration and shock, and can also be manufactured into various shapes by powder pressing, which is widely used in various small devices. Moreover, due to its precise chemical composition and uniform structure, the magnetic properties of sintered Alnico are thus uniform and stable. Because of the process and economic advantages of sintered Alnico magnets, they are widely used in the electrical instrumentation, radio, and automatic control industries.

In the manufacturing process of sintered aluminum-nickel-cobalt, aluminum has a low melting point, about 660˚C, and poor oxidation resistance, and the melting points of other metal components in the sintering alnico magnets are higher than it, so aluminum is added in the form of intermediate alloys, such as iron-aluminum alloy or cobalt-aluminum alloy. In order to get larger coarse grains and better magnetic properties, usually, there are four kinds of single-element powder, nickel powder, cobalt powder, iron powder, and copper powder, and four kinds of intermediate alloy powder, iron-aluminum alloy, cobalt-aluminum alloy, niobium-iron alloy, and titanium-iron alloy, in the process. They are weighed separately and mixed well to produce sintered AlNiCo magnets. Unlike foreign sintered Alnico production process, the domestic sintered Alnico in China has more reasonable powder froth particles in the production process, and there is no need to add binder in the pressing and forming process, thus making the sintering process without the need to discharge the gas volatilized by the binder, thus in terms of magnetic properties, it is better than the foreign manufacturers. Therefore, some micro BLDC motors usually use sintered alnico magnets from Chinese manufacturers. Our manufacturing process reduces the intermediate alloy powder to 2 types Cobalt-Aluminum alloy and Titanium-iron ally and more pure elements powers to increase the magnetic properties and their stabilities.

alnico magnet

Compared with cast Alnico, the density of sintered Alnico is lower than cast Alnico because of the different manufacturing processes, so the magnetic property of the same grade of sintered Alnico magnets are somewhat lower than that of cast Alnico magnets. Take Alnico 5 as an example, using the IEC naming method, sintered Alnico magnet is usually Alnico 34/5, where 34 means the size of magnetic energy product, 34 kJ/m3, and the coercivity is close to 50 kA/m, which is about 48 kA/m. Cast Alnico is often named Alnico 37/5, with a magnetic energy product of 37 kJ/m3, and the remanence is usually higher than that of sintered Alnico magnet, about 12,500 Gs.

But sintered Alnico magnets can avoid the defects of cast Alnico magnets. Casting Alnico magnets using the atmospheric melting method, the cast alnico magnets are easy to have the defects of sand holes and pores inside, which will affect the magnetic performance of magnets, and the material composition is not very uniform, and the dispersion of the product performance is relatively large. because the production process is limited, small products cannot be formed. Smaller products need to be processed by wire cutting and other machining processes. Sintered Alnico can just make up for these shortcomings. Therefore, sintered Alnico magnets are often used to produce smaller products, direct pressing form, and cost reduction. It is used for low-voltage products such as decouplers and relays, as well as some automotive sensors, etc.

Manufacturing Process of sintered alnico magnet

Vacuum melting of intermediate alloys

Intermediate alloy is a relatively important part of sintered AlNiCo magnet manufacturing process because aluminum has a relatively low melting point and is highly susceptible to oxidation, which cannot be done in a pure powder state, and titanium is also highly susceptible to oxidation, so these two metals need to be made into powder in an alloy state. Other manufacturers also use iron-aluminum alloy, we are now improving the process, mainly with these two intermediate alloys to make powder.

Powder Intermediate Alloys

The intermediate alloy needs to be crushed first and then grind into powder. In the old version of the process, the powder is ground by steel balls, because the powder should be finer than 150 mesh, so the use of steel ball milling equipment requires repeated grinding and sieving with a sieve. Now the steel balls are replaced by an airflow mill, and the powder size is more uniform.

Hydrogen Reduction Powder Material

Iron powder, cobalt powder, copper powder, and nickel powder, these several high purity metal powders will have an oxide, so these metals need to be thermally reduced. Usually, ammonia decomposition devices are used to produce hydrogen gas to reduce these metal powders, in the thermal reduction vessel for 2 hours, and hydrogen gas protection is also required for cooling.

Mixing Metal Powder Materials

Calculate the weight needed for each kind of metal powder, weigh it with an electronic scale, mix it in proportion, and need to put it in the mixing equipment for repeated mixing for 60 minutes to make the composition more even. Then use the vacuum packaging machine packaging to prevent moisture or oxidation when preserving.

Press and forming

Sintered Alnico magnets are more distinctive among all magnetic materials in terms of press forming. First of all, sintered Alnico magnet does not need to be oriented in the press forming process even if it is an anisotropic grade(like Alnico 8 magnet). Therefore, the press machine for forming does not need to have a magnetic field. (NdFeB and SmCo magnets need a magnetic field to be oriented in the magnetic direction in the press forming process) Secondly, the advantage of sintered Alnico is small products, so it is basically a single piece forming in place, not like NdFeB or SmCo magnets, which are formed into large squares or cylinders and require subsequent wire cutting processing. Therefore, the pressure used for sintered Alnico magnets is relatively small, 10T-50T press machines can meet the requirements. Only a small amount of forming agent (stearate) is added during the mixing process to facilitate the pressing and forming.

Sintering Process

The sintering process of sintered Alnico magnet is done in a vacuum sintering furnace and the sintering process goes through several temperature intervals and can go through 6-8 steps. The highest sintering temperature can reach around 1400˚C and requires holding and ramping steps at different temperature stages. This allows the sintered Alnico to produce the desired grain size inside the sintered Alnico and the density of the product after sintering.

Heat Treatment

The heat treatment process for sintered Alnico magnets doesn’t not in the vacuum sintering furnace where NdFeB and SmCo are carried out in the vacuum sintering furnace. The heat treatment of sintered Alnico magnets can be divided into several steps. a pretreatment between 800 and 900˚C for 30-50 minutes, a solid melt heat treatment between 1260 and 1280˚C for roughly 30 minutes, and then cooled down by air cooling. The anisotropic ones will be put into a magnetic field furnace with a furnace temperature of 750˚C to 850˚C for 20-30 minutes of orientation and further tempering treatment. It is between 500-650˚C. After such a complex heat treatment process, the magnets will have magnetic properties. A proper heat treatment process ensures the precipitation of α1 and α2 phases and reduces and suppresses the precipitation of γ phases. This is because the γ phase is detrimental to the magnetic properties. the isotropic materials like Alnico 2 and Alnico 7, don’t need to be heat treated in a magnetic field to be oriented. but the anisotropic materials like Alnico 5, and Alnico 8, need to be oriented in a magnetic field during the heat treatment at a temperature of about 750˚C to 850˚C, they different materials would request different temperatures.


Because most magnetic materials are very brittle, machining methods are relatively limited. Grinding is the most common machining method. Because most sintered AlNiCo magnets are small products that are almost to size in the forming stage, most require only simple grinding machining processes. There are also some products that can be divided into rough machining, placed in front of the heat treatment process, and then when the heat treatment is complete, then finish machining is performed to grind the product to the size and tolerance requirements. A few sintered Alnico products will use other processing methods, such as wire cutting, turning, etc. For special size processing.

Magnetic Properties of Sintered Alnico Magnet

The Grades SAlnico N/M- S means Sintered,  N means (BH)max kJ/M3, M means Coercivity kA/m. China Grades FLNG+number, the F means powder sintered, LNG means Alnico, the number means (BH)max. The T means Titanium material, for Alnico 6,7,8.

MMPA – US standard, Alnico 7 is the isotropic version Alnico 8. 

The properties of Alnico magnets can be adjusted to some degree from the standard material properties, depending on the customer’s requirements. That is why, some new properties are added to our material grades and the European standard IEC and the American standard MMPA.

Grade (IEC) Remanence(Br) Coercivity(Hcb) Intrinsic Coercive(Hcj) Max.BH.Product China Grade MMPA
T(kGs) kA/m(kOe) kA/m(kOe) kJ/m3(MGOe)
SAlNiCo4/1 0.87-0.89
SAlNiCo8/5 0.53-0.62
SAlNiCo10/5 0.63-0.70
SAlNiCo12/5 0.70-0.75
FLNG12 Alnico 2
SAlNiCo14/5 0.73-0.80
SAlNiCo14/6 0.62-0.81
SAlNiCo14/8 0.55-0.61
SAlNiCo18/10 0.57-0.62
FLNGT18 Alnico 7
SAlNiCo29/6 0.97-1.20
FLNGT28 Alnico6
SAlNiCo30/6 1.00-1.10
SAlNiCo42/10 0.95-1.10
SAlNiCo33/11 0.70-0.80
FLNGT33 Alnico8
SANiCo35/5 1.10-1.20
FLNG35 Alnico 5
SAlNiCo37/15 0.70-0.80
FLNGT37J Alnico8HC
SAlNiCo39/12 0.83-0.90
SAlNiCo44/12 0.90-0.95
SAlNiCo40/15 0.75-0.85
SAlNiCo44/15 0.80-0.88