Study On Nd-Fe-B Sintered Permanent Magnets Produced By Modifying Intergranular Phase

Nd-Fe-B sintered magnets have been widely used in various applications due to their outstanding magnetic properties,and become the best important permanent magnets.However, poor corrosion resistance and low coercivity limit their applications and development.Both corrosion resistance and coercivity are very sensitive to intergranular phase.Therefore, modifying intergranular phase are very effective methods to improve both corrosion resistance and coercivity of Nd-Fe-B sintered magnets.In this dissertation,Nd-Fe-B sintered magnets were prepared by single alloy sintering method and binary alloy sintering method,respectively.Microstructure,corrosion resistance and coercivity of Nd-Fe-B sintered magnets with intergranular addition of Cu₆₀Zn₄₀ and Mg₇₀Zn₃₀ powders were systematically investigated and analyzed,respectively.Meanwhile,the intergranular phase was modified by adding(Pr,Nd)_32.5Fe₆₂Cu_5.5 alloy,and microstructure, corrosion resistance and coercivity of Nd-Fe-B sintered magnets were systematically investigated.The design principle of Nd-Fe-B sintered magnets with high corrosion resistance was suggested.The main results are as follows:Both corrosion resistance and magnetic properties of Nd-Fe-B sintered magnets are effectively improved with intergranular addition of Cu₆₀Zn₄₀ and Mg₇₀Zn₃₀ powders, respectively.Enhancement of the electrochemical potential of the intergranular phase,decrease of the total contents of Nd.uniform distribution of the Nd-rich phase and increase of magnet density are responsible for the corrosion resistance improvement.Especially.the corrosion resistance of magnets with intergranular addition of Cu₆₀Zn₄₀ powders is improved approximately one order of magnitude in 3.5 wt%NaCl solution.Moreover,the uniform distribution of Nd-rich phase and grains refined resulting in the enhancement of coercivity,and the increase of magnet density leading to the improvement of remanence and maximum energy product.Modifying intergranular phase by adding(Pr,Nd)_32.5Fe₆₂Cu_5.5 alloy can effectively improve corrosion resistance and coercivity of Nd-Fe-B sintered magnets.Corrosion current density of magnet with 12 wt%(Pr,Nd)_32.5Fe₆₂Cu_5.5 alloy and RE_30.2B_0.96Fe_bal magnets prepared by single alloy sintering method are 3.484μA/cm² and 9.870μA/cm² in 3.5 wt%NaCl solution, respectively,exhibiting that the corrosion resistance of magnets with the addition of (Pr,Nd)_32.5Fe₆₂Cu_5.5 alloy is effectively improved.Meanwhile,the enhancement of coercivity is about 69%in the case of 12 wt%(Pr,Nd)_32.5Fe₆₂Cu_5.5 alloy addition compared with that for additive-free magnet.