Study On Soft Magnetic Properties,Crystallization Mechanism,and Corrosion Behavior Of Fe-based Nanocrystalline Alloys By Aluminum Doping

The research on Fe-based nanocrystalline soft magnetic alloys mainly focuses on improving the magnetic properties of the material itself.However,when iron-based nanocrystalline soft magnetic alloys are used in complex and harsh environments（such as a humid atmosphere rich in chloride ions）,they will face problems such as corrosion and the resulting deterioration of magnetic properties.Therefore,it is necessary to obtain iron-based nanocrystalline alloys with excellent soft magnetic properties and corrosion resistance through composition design and heat treatment process control.However,there are few studies on the effects of aluminum（Al）doping on the magnetic properties and corrosion properties of iron-based nanocrystalline alloys.In this paper,the soft magnetic properties and corrosion resistance of Fe_75.8Si₁₂B₈Nb_2.6Cu_0.6P₁（Al0）alloys are regulated by the Al element doping and heat treatment process.On the one hand,it is revealed that Al doping affects the alloys and the soft magnetic properties of this series of alloys.On the other hand,the effects of heat treatment temperature and Al element content on the corrosion resistance of this series of alloys in 3.5wt.%Na Cl solution was explored,and the relevant corrosion mechanism model was established.The main results are as follows:（1）Al element doping optimizes the soft magnetic properties and heat treatment process stability of Fe Si BNb Cu PAl alloy.The Al content was increased from 0 to 6 at.%,the heat treatment temperature rangeΔT of the alloy was widened from 172 K to 205 K,and the 1 k Hz magnetic permeability（μ_e）of the nanocrystalline alloy was increased from 27000 to 30000,and the coercivity（H_c）was decreased from 0.78 A/m to 0.35 A/m.Because the Al-doped alloys formed high-density fine and uniform nano-grains after crystallization,and Al and Si elements were dissolved inα-Fe together to form theα-Fe（Si,Al）phase,which reduces the magnetic anisotropy of the grains,thereby optimizing the soft magnetic properties of the alloy.In addition,the Al0 alloy was annealed at 843 K for 1 h,the H_c was about 27 A/m and theμ_e decreased to below 10000;the Al6 alloy was annealed at 843 K for 2 h,and the H_c remained below 1 A/m,while theμ_e remained above 25000.Because the doping of the Al element effectively inhibits the precipitation of hard magnetic phases such as Fe₂B and Fe₂₃B₆,the alloy exhibits high heat treatment process stability.（2）Appropriate heat treatment process and Al content make Fe Si BNb Cu PA1nanocrystalline alloy have both excellent soft magnetic properties and corrosion resistance.The corrosion resistance of Al0 alloy is sensitive to the heat treatment temperature.After heat treatment at 903 K for 30 min,Fe,Si,and Nb elements are enriched in the alloy,so Si and Nb oxides cooperate to form a dense insoluble protective layer during the corrosion process,which improves the corrosion resistance of the alloy.After doping with the Al element,the nanocrystalline alloy is enriched with the Al element.After contacting the corrosive medium during the corrosion process,Al₂O₃ oxide film is preferentially reacted on the surface of the alloy,which hinders charge transfer and ion exchange at the solid-liquid interface,thereby protecting other elements that do not corrode further,improving the corrosion resistance of the alloy.