Magnetic properties of alnico 8 sintered magnets produced by powder injection moulding

摘要

Magnets of the alnico group have a several times lower energy product compared to Re-Co and NdFeB magnets. However application of these latter magnets is limited by the maximum operating temperature of 180°C for NdFeB and about 350°C for Re-Co compared to 540°C for alnico. Additionally, mechanical properties and thermal stability of magnetic properties, which are also important in practice, are much higher for alnico. PIM (powder injection moulding technology] is used for large scale manufacturing of small and highly complex parts, making it attractive to introduce alnico in PIM since complex-shaped anisotropic components can be obtained. This was studied in the present work. First the alnico 8 starting powder was additionally milled until a mean particle size of d_(80)=8 μm was attained. Properties of the original-as-received and as-milled powder were investigated using SEM and XRD analysis. The milled powder was then mixed with a solvent-type binder. The feedstock thus prepared was injected into a cylindrical mould. This step was then followed by debinding and sintering. Different sintering temperatures and times were used in order to optimise the sintering process. The C, S, N and 0 contents in the samples were measured. Thermomagnetic treatments of the sintered samples were performed in order to obtain optimal magnetic properties. These were measured on sintered samples before, between and after thermomagnetic treatment processes. The final maximum magnetic energy product value obtained for the currently applied optimal sintering conditions ((BxH)_(max) = 22.95 kJ/m~3) was not as high as the ones obtained using classical methods for alnico manufacturing, but acceptable for a first attempt. Thus it can be concluded that application of PIM in manufacturing of alnico magnets with complex shapes is possible but requires further optimisation of the sintering and thermomagnetic treatment processes and also of the debinding procedure since the content of C and 0 in the samples also needs to be reduced.