Microstructure And Properties Of Magnetic Nd₂Fe₁₄B_p/Al Composites Prepared By Microwave Sintering

The motor magnetic components of new energy vehicles have need of lightweight and miniaturization,the current way to lose weight is to use aluminum steel,carbon fiber composite materials replace traditional steel structural materials,but has not yet involved the weight reduction of large amount of magnetic materials and the strength and toughness of the device to improve the processing and safety performance.The existing Nd₂Fe₁₄B magnetic materials have the best comprehensive magnetic properties,but it has high density,poor electrical and heat conductivity,brittleness and difficult to be processed.It can not meet the requirements of lightweight and safe use of magnetic devices.When Al is used as matrix and Nd₂Fe₁₄B magnetic powder is used as composite phase,Al matrix composites are expected to achieve lightweight,high strength and toughness,and high thermal conductivity.In this study,Nd₂Fe₁₄B was used as the reinforcing phase,and we used microwave sintering technology to replace the conventional sintering process in the production of Nd₂Fe₁₄B_p/Al composites by the traditional powder metallurgy approach.By adjusting the process parameters to optimize the microstructure and magnetic properties,a new type of magnetic aluminum matrix composites with integrated structure and function was obtained.The respective advantages of matrix and reforced phase in aluminum matrix composites were brought into full play.The microstructure and phase composition of the materials were analyzed by means of SEM and XRD,nano-indentation and other modern material detection methods,and the density,hardness,compressive strength and magnetic properties,including coercivity（H_c）,remanence（B_r）,maximum magnetic energy product(（BH）_max)and saturation magnetization（M_s）were also measured.The main conclusions were summarized as follows:（1）The DSC and XRD phase analysis of Nd₂Fe₁₄B_p/Al composites prepared by microwave sintering shows that only matrix phase Al and reinforced phase Nd₂Fe₁₄B exist in the composites and no other new generated phases in the composites.（2）The microstructure of the composite prepared by microwave sintering is related to powder size,the content of Nd₂Fe₁₄B and sintering temperature.The finer of the powder size,Nd₂Fe₁₄B_p/Al composites have the higher relative density.When the content of Nd₂Fe₁₄B was15wt.%,and the sintering temperature was 580℃,the particle dispersion is relatively uniform and the microstructure stability of the composites is the best.The compactness is 92%,and the compressive strength and yield strength of the samples are 222MPa and 168MPa respectively,which are increased by 28%and 21%,respectively compared with the sample of pure aluminum sintered at 580℃.（3）The magnetic properties of the composites sintered at different temperatures were tested and the results show that when sintered at 580℃,the sample have the best magnetic properties.The coercivity（H_c）,remanence（B_r）,maximum magnetic energy product(（BH）_max)and saturation magnetization（M_s）are 0.61T,0.60T,59.89kJ/m³ and 152emu/g respectively.（4）Co has an effect on the microstructure and magnetic properties of the composites,and Co is mainly distributed at the phase boundary and has the effect of grain refinement.When the content of Co was 5wt.%,the sample have stable structure and best magnetic properties.Compared with Nd₂Fe₁₄B_p/Al composites（0wt.%Co）,the magnetic properties of the sample have significant changes.When the Co content was 5wt.%,the maximum values of the coercivity（H_c）,remanence（B_r）,maximum magnetic energy product(（BH）_max)and saturation magnetization（M_s）are 0.80T,0.73T,88.63kJ/m³ and 251emu/g,respectively.（5）The effects of microwave and conventional sintering on the microstructure and properties of Nd₂Fe₁₄B_p/Al composites were studied.The results show that microwave sintering are better than conventional sintering,and the structure of sample are more uniform and have better mechanical and magnetic properties.