Alnico . Alnic or alnico is an alloy formed mainly of cobalt , aluminum and nickel , although it can also contain iron , copper and sometimes titanium . Its main use is in magnetic applications.
Alnicus is an acronym, and refers to metal alloys that are mainly composed of aluminum (Al symbol), nickel (Ni symbol) and cobalt (Co symbol), therefore al-ni-co, with the addition of iron , copper , and sometimes titanium , usually Al 8-12%, 15-26% Ni, 5.24% Co, up to 6% Cu, up to 1% Ti, and the rest of Fe.
Alnic alloys are ferromagnetic and are used to make permanent magnets. Before the development of rare earth magnets in the 1970s, they were the strongest type of magnet . Other trade names for the alloys in this family are: Alni, Alcomax, Hycomax, Columax, and Ticonal.
Summary
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- 1 Beginnings of the alnico
- 2 Properties
- 1 Collection and characteristics
- 3 Uses
- 4 Types of Alnico
- 5 Sources
Beginnings of the alnico
The development of alnicus began in 1931 , when T. Mishima in Japan discovered that an alloy of iron , nickel , and aluminum had a magnetic coercivity ( resistance to loss of magnetism) of 400 Oersted, twice the best magnet steels in The time.
Properties
Alnic alloys make strong permanent magnets and can be magnetized to produce strong magnetic fields. Of the most commonly available magnets, only rare earth magnets like neodymium and samarium-cobalt are stronger. Alnico magnets may produce forces of the magnetic field at the poles as high as 1500 gauss (0.15 tesla) or about 3000 times the strength of the magnetic field of the Earth. Some brands of alnico are isotropic and can be magnetized efficiently in any direction. Other types, such as alnico 5 and alnico 8, are anisotropic, each with a preferred direction of magnetization or orientation. Anisotropic alloys generally have a higher magnetic capacity in a preferred orientation than isotropic types. The alnico remanence (Br) may be greater than 12,000 gauss (1.2 T), its coercivity (Hc) may be up to 1000 Oersted (80 kA / m), its product of energy ((BH) max) may be up to 5.5 mg • Oe (about 44 T / m). This means that alnico can produce a magnetic flux in the closed magnetic circuit, but has relatively little resistance to demagnetization.
Obtaining and characteristics
Alnico parts and components are produced by molding or sintering processes. Anisotropic alnico magnets are oriented by heating above a critical temperature , and cooling in the presence of a magnetic field . Both isotropic and anisotropic alnicos require adequate heat treatment for optimal development of magnetic properties – without which their coercivity is about 10 Oe, comparable to that of technical iron , which is a soft magnetic material. After heat treatment the alnic becomes a composite material, called precipitation material, which is made up of iron and cobaltprecipitated in a matrix rich in Ni and Al.
The anisotropic alnic is oriented along the desired magnetic axis by applying an external magnetic field to it during nucleation of precipitated particles , which are produced with a cooling of 900 ° C (1,650 ° F) to 800 ° C (1,470 º F), near the Curie point. Without an external field there are local anisotropies of different orientations, due to spontaneous magnetization. The precipitate structure is a “barrier” against changes in magnetization, as it prefers some magnetizing states that require a lot of energy to obtain the material in any intermediate state. Furthermore, a weak magnetic field changes the magnetization of the single matrix phase, and is reversible.
Alnic alloys have some of the highest Curie points of any magnetic material, around 800 ° C (1,470 ° F), although the maximum temperature is normally limited to about 538 ° C (1,000 ° F). They are the only magnets that have useful magnetism even when heated red-hot.
This property, as well as its fragility and high melting point , is the result of the strong tendency towards order, due to the link between aluminum intermetallics and its other components. They are also one of the most stable magnets if handled properly.
Applications
Alnico magnets are widely used in consumer and industrial applications where strong permanent magnets are needed; As in electric motors, electric guitar pickups , microphones, sensors, speakers, and horseshoe magnets . In many applications they are being replaced by rare earth magnets, whose stronger fields (Br) and larger energy products (BHmax) allow smaller magnets to use them for a given application.
Alnico Types
Based on the preparation process, and the different uses, alnico alloys can be classified into three main types:
- Cast steel alloy
- Sintered Alnico
- Steel alloy bar
