Low-dose damage evolution in pure magnesium under electron irradiation: Effect of foil orientation and pre-existing dislocations

•Damage evolution in Mg has been studied with 200 keV electron irradiation at RT.•The occurrence of visible damage required incubation due to low electron flux.•Irradiation defects consisted of basal-plane ⅙ loops, exclusively.•The [12¯10] foil orientation favoured loop growth and population increase.•Pre-existing dislocations (1014 m−2) suppressed the build-up of loop population. Low-dose damage evolution in commercial purity (99.95 wt%) magnesium has been investigated, under 200 keV electron irradiation at room temperature, up to ∼0.03 displacements per atom. Quantitative defect production and evolution statistics were obtained for two types of prism foils (z = [12¯10], [101¯0]), in samples of as-received and heat-treated (400 °C/1 h) condition. An incubation period was found to produce visible damage in all samples, in correspondence with about ⅓ of the maximum dose. The damage microstructure consisted of basal-plane 16 loops, exclusively; while no voids were observed throughout the course of irradiations. Steady-state accumulation of dislocation loops was found at doses beyond the incubation limit in heat-treated samples. Higher loop number density and large loop average size were confirmed in [12¯10] than in [101¯0]. One-dimensional loop rafts were developed via elastic interaction. In as-received samples, the presence of pre-existing dislocations (on the order of 1014 m−2) gave rise to suppressed build-up of loop population. Saturation of loop growth was confirmed, when loop average size reached ∼20 nm. Underlying mechanisms of foil orientation effect and pre-existing dislocation effect upon microstructure development are discussed. The paper concludes with a brief comparison between electron irradiation and fission neutron irradiation in magnesium, aiming to bring new insights upon displacement damage studies in materials with hexagonal close-packed structure.