The magnetic field is a kind of non-contact, green, high-energy, multi-effect physical field, which can change the material preparation process conditions of thermodynamics and kinetics and transfer high intensity energy to the atomic scale of matter without contact. Moreover, it directly affects the material’s migration, matching, and arrangement of atoms, molecules, ions, or grain. The magnetic field has a great and profound effect on the microstructure and properties of materials ^[1][2][1,2].

Since the 1960s, when scholars found that magnetic field can affect the microstructure and mechanical properties of ferromagnetic materials ^[3][4][3,4], they tried to use the magnetic field to treat non-ferromagnetic materials and also found that it can affect material structure and properties ^[5][6][5,6]. Therefore, magnetic field treatment in material modification has been rapidly and widely concerned and has become an important technical means to develop new materials and optimize material properties.

In recent years, researchers have been using the magnetic field to regulate the structure and properties of different magnetic materials. With the deepening of research, many new magnetic phenomena have been discovered. Utilizing electromagnetic stirring technology, the magnetic field achieved significant advancements that improved the microstructure and characteristics of the metal solidification process. It gradually regulates the direction of the microstructure and properties of the solid metal material development, mainly reflected in magnetic field-assisted metal material heat treatment, assisted plastic deformation, and independently treated metal materials to improve material structure and properties ^{[7][8][9][10]}[7,8,9,10], which have achieved good results.

To eliminate the residual internal stress generated by the high temperature gradient and quick solidification of Ti-6.0Al-4.4V alloy during selective laser melting (SLM) process, as well as to optimize the microstructure and properties, the magnetic field-assisted annealing treatment was performed under a magnetic field induction intensity of 2–10 T magnetic field induction intensity ^[11][12][11,12]. The annealing temperature was 400 °C, and the annealing time was 30 min.

Under the coupling effect of temperature and magnetic field, the α’ phase of martensite was promoted to transform into α + β phase, and the width of α’/α phase was reduced and more refined. Meanwhile, when the magnetic induction intensity is 8 T, the alloy elongation reaches 15.1%, which was increased by 62.4% compared with 9.3% without the magnetic field. The tensile strength of the alloy was slightly increased by 2.8%. The strength and plasticity of Ti-6.0Al-4.4V alloy are improved synchronously by the magnetic field.

To study the influence of magnetic field on the properties of different magnetic metals, high-purity Al, Ni, and Cu samples were firstly stressed, relieving annealing, then subjected to 30% compression deformation, and finally subjected to heat preservation and alternating magnetic field [13]. With the increase of magnetic induction intensity, the microhardness of paramagnetic pure Al and Ni (temperature above Curie point) gradually increased, while the microhardness of ferromagnetic pure Ni (temperature below Curie point) and diamagnetic pure Cu steadily declined. The microhardness of alloys increased by 8.6%, increased by 5.9%, decreased by 6.2%, and decreased by 12.3%, respectively, compared with that without a magnetic field. It found that the microhardness of different magnetic metals is not consistent when the magnetic field assisted heat treatment.

After solid solution, the sample of paramagnetic Al-5%Cu alloy aged at 130 °C, and a pulsed magnetic field was applied [14]. Compared with that without magnetic field after three hours of aging, more Al₂Cu phase was dispersed and precipitated inside the alloy, and the hardness value increased by 30.0% to 115.2 HV.

The paramagnetic AA2219 aluminum alloy was solid solution after forging, and an alternating magnetic field was applied during the subsequent aging process [15]. It was found that the microhardness of the alloy with magnetic field was higher than that without magnetic field at the same aging time. After 8 h of aging, the alloyʹs microhardness with magnetic field increased by 10.7% compared with that without magnetic field. The changes of microhardness of the alloy was mainly due to the magnetic field affecting the number and distribution of θʹ phase precipitation.

Diamagnetic beryllium bronze alloy, which had been solid solution treatment, was aged in the constant magnetic field of 0.7 T ^{[16][17][18][19]}[16,17,18,19]. It can be found that the microhardness of beryllium bronze alloy decreases basically, and the microhardness of Cu-1.6Be alloy decreases by 25.0% at most after magnetic field treatment. However, the microhardness of Cu-1.9Be-0.33Ni alloy increased by 38.0% after the addition of the Ni element.

According to the above research contents ^{[11][12][13][14][15][16][17][18][19][20][21]}[11,12,13,14,15,16,17,18,19,20,21], the changes in microhardness of magnetic field-assisted heat treatment of aluminum and aluminum alloy, beryllium-bronze alloy, and titanium alloy compared with that without magnetic field are sorted into Table 1. It can be seen from Table 1 that the magnetic field can significantly change the hardness of the alloy during metal heat treatment assisted by a magnetic field. In particular, magnetic field-assisted annealing can significantly improve the plasticity of Ti-6.0Al-4.4V alloy prepared by selective laser melting process.

Analyzing the microhardness changes of beryllium bronze alloys No. 7–14 in Table 1 found that the microhardness of beryllium bronze alloys without the addition of Ni element (No. 10 except) decreased with magnetic field-assisted aging. In contrast, the microhardness of alloys containing the Ni element added increases. Analyzing the microhardness changes of aluminum alloys No. 15–18 in Table 1 found that the microhardness of aluminum alloys increased with magnetic field-assisted aging as compared to that without a magnetic field. However, only the microhardness of No. 7 aluminum alloy containing the Fe element decreased. After applying the magnetic field, the microhardness of beryllium bronze alloy containing Ni and aluminum alloy containing Fe showed a different trend from that of other alloys without adding Ni or Fe whether this phenomenon is related to the ferromagnetic Fe and Ni element, and the influence of ferromagnetic elements on the properties of alloys with paramagnetic or diamagnetic base, which is worth further study.