Influence of Pulse Time on Microstructure and Properties of AZ31B Magnesium Alloy Surface Modified by High-Current Pulsed Electron Beam

AZ31B magnesium alloy was irradiated by high-current pulsed electron beam, and the surface morphology, phase composition, grain size, hardness and wear resistance of the alloy under different pulse times (3,5,7) were investigated and compared with those of unirradiated alloy. The results show that high-current pulsed electron beam irradiation did not change the phase composition of the alloy, but made the Mg₁₇Al₁₂ second phase particles which originally distributed at the grain boundaries disperse. After irradiation, melting pits appeared on the alloy surface, and the surface roughness increased. With the increase of pulse time, the number of melting pits decreased and its size increased, and the surface roughness of the alloy decreased. There were no obvious defects on the surface of the alloy after three-pulse and five-pulse irradiation, while a few micro-cracks existed on the surface after seven-pulse irradiation. After irradiation, there were a large number of twins on the surface of the alloy, and the grain size decreased obviously. With the increase of pulse time, the grain size decreased slightly. There were large grains and twins in the alloy irradiated for seven pulses, and the grain size distribution was not uniform. With the increase of pulse time, the average hardness of the alloy surface increased. The average hardness after seven-pulse irradiation increased by about 29% compared with that of the unirradiated alloy, but the hardness uniformity was poor. Compared with that of the unirradiated alloy, the wear volume after three-pulse and five-pulse irradiation was smaller, while the wear volume after seven-pulse irradiation was larger. The wear volume after five-pulse irradiation was the smallest, and the wear resistance of the alloy was the best. After five-pulse irradiation, the alloy had the best comprehensive performance; compared with those of the unirradiated alloy, its average grain size decreased by about 32%, the average hardness increased by about 23%, and the wear volume decreased by about 27%.