Analysis of the optimal heat treatment temperature for AlNiCo-based semi-hard magnetic materials based on temperature-dependent yield strength prediction model

To improve the starting characteristics of permanent magnet hysteresis motors, AlNiCo-based on semi-hard magnetic materials (ASMM) is proposed. The microstructural design is carried out by combining the advantages of soft magnetic composites (SMCs) and AlNiCo8 while choosing BaTiO₃ with the negative thermal expansion property to eliminate the voids. The material composition as well as the range of heat treatment temperatures are determined by the phase transition kinetics. The temperature-dependent yield strength prediction model considering stress-equivalent magnetic fields is then developed. The model establishes the quantitative relationship between yield strength, ambient temperature, magnetostriction coefficient, elastic modulus, and Poisson's ratio. The comparisons between the model and experiments are made. It can be obtained that the yield strain is related to the microstructure and morphology, and the optimum heat treatment temperature is 680°C under the condition of ensuring the highest yield strength. This method can be used to optimize the parameters of the material preparation process and provide a reference for the optimized design of high-speed and ultra-high-speed motors.