7N01アルミニウム合金の冷間加工性に及ぼす第2相析出状態の影響

抄録

Japanese Industrial Specification recommends Al-Zn-Mg alloys are annealed at 688K followed by furnace cooling. However sometimes the cold working (drawing or rolling) of annealed material in the above condition becomes more difficult because of natural age hardening. In this study, the effect of annealing temperature (493-683K) on both mechanical property and cold workability in annealed Al-Zn-Mg extruded bars was investigated from the view point of precipitation of second-phase particles. In the case of annealing at 573K or less, high elongation, low tensile and yield strength were obtained compared with annealing at 683K, and furthermore the hardness was not changed during room temperature aging. The material annealed at 548K can be rolled up to 95% reduction without edge cracking. However, edge cracking with shearing was occurred at 80-85% reduction in the material annealed at 683K. A lot of particles with a diameter of about 0.1μm, which are estimated as MgZn₂-phase precipitates having no coherency with matrix, were observed in annealing at low temperature. While, these particles were reduced at annealing at 683K and solute atoms increased. The reason why cold workability of materials annealed at low temperature was improved is that homogeneous deformation occurs and shearing fracture is inhibited because of dynamic recovery around particles.