【摘要】 采用拉伸试验和双剪试验，结合金相显微镜（OM）、电子背散射衍射（EBSD）和透射电子显微镜（TEM）观察，研究了退火热处理对5056铝合金线材组织和性能的影响。结果表明，与冷拉态线材相比，经250℃/2 h退火处理后5056铝合金线材组织形貌与冷拉态基本一致，以变形态组织为主，内部发生了回复和少量再结晶；经280℃/2 h退火处理后5056铝合金线材组织基本完成再结晶，此后升高退火温度或延长退火时间均未显著影响线材的晶粒组织形貌。随退火温度的升高，5056铝合金线材的强度先降低后在退火温度为280℃（即再结晶基本完成的温度）时保持稳定，延伸率则是整体呈现增加的趋势；在280℃下延长保温时间，线材的力学性能未随退火制度的变化而显著改变。因此确定280℃/2 h为适宜的退火制度，该制度下5056铝合金线材抗拉强度为288 MPa，屈服强度为140 MPa，剪切强度为177 MPa，延伸率为32.4%。更多还原

【Abstract】 5056 aluminum alloy is an Al-Mg alloy with high plasticity, medium strength and excellent corrosion resistance in the annealed heat treatment condition, and high quality 5056 aluminum alloy wire has become the main raw material for aerospace core rivets. In this work, the influence of annealing heat treatment on microstructure and properties of 5056 aluminum alloy wire was investigated by tensile test, double-shear test, optical microscopy(OM), electron back-scattered diffraction(EBSD) and transmission electron microscopy(TEM), and the correlation between the microstructure and properties of 5056 wire was also discussed. The evolution of the microstructure and properties of the wire with 44.3% cold-drawn deformation in the final pass was studied during the complete annealing heat treatment. The results indicated that, compared with the cold-drawn wire, a small amount of recovery occurred after annealing at 250 ℃ for 2 h, but the deformation microstructure was still dominant, and there was a high density of dislocation entanglement and a small amount of substructure in the matrix. The degree of recovery increased after annealing at 260 ℃ for 2 h, and significant recrystallization occurred after annealing at 270 ℃ for 2 h, indicating that the average orientation difference fraction of 0～1°grains in the fully recrystallized ratio was 95.3%. The wire had completed recrystallized after annealing at 280 ℃ for 2 h, and the degree of recrystallization reached 98.8%, meanwhile the grains was uniform and fine. The recrystallization ratio did not change significantly after the annealing temperature subsequently increased again. Therefore, neither increasing the annealing temperature nor extending the annealing time significantly affected the average grain size of the wire. The reason for this might be that the driving force of the increased temperature could not offset the resistance to grain boundary migration, or it might be that the nanoscale insoluble second phases like Al6(Mn, Si, Cr), Al6(Mn, Fe, Si), Al6(Fe, Mn) and Al13CrMn distributed on the grain boundaries, which prevented the migration of high-angle grain boundaries. With the increase of annealing temperature, the degree of structural homogeneity also underwent an increase and then a decrease. This was due to the formation of high-density dislocation entanglement after cold drawing for recrystallization provided a large number of cores, to meet the thermodynamic conditions of recrystallization occurring, the recrystallized core could grow up uniformly in the matrix and form non-strain recrystallized grains. With the increase of recrystallization, the new strain-free recrystallized grains gradually replaced the deformed grains within the wire, due to the recrystallized grains were more uniform and fine, so the heat treatment temperature ranging from 250 to 280 ℃, the uniformity of microstructure in wire also increased. The wire completely recrystallized after annealed at 280 ℃ based on EBSD results. After that, the recrystallized grains grew up with rising the annealing temperature, the uniformity of the microstructure decreased, meanwhile the degree of fineness decreased.Compared with the cold-drawn state wire, the strength of the annealed wire reduced and the elongation increased, indicating that the annealing heat treatment could effectively offset the work-hardening effect and improve the plastic processing performance. The strength of the wire decreased with annealing temperature ranging from 250 to 280 ℃, while the elongation increased. When the annealing temperature ranged from 280 to 400 ℃, the tensile strength, yield strength and shear strength was 290 MPa, 135 MPa and 175 MPa, respectively, and the elongation showed an overall increasing trend. The shear strength decreased with annealing temperature from 250 to 280 ℃, and remained at the same level of about 177 MPa between 280 and 400 ℃. However, compared with the tensile properties, the shear strength was less affected by the annealing temperature. In summary, the annealing treatment reduced the strength of the wire, increased its elongation, led to a certain softening effect to the wire, and its plastic processing properties were improved. In addition, the mechanical properties of the wires remained at the same level after recrystallization occurred. As for the effect of annealing time, it was found that the extension of annealing time had almost no effect on the tensile strength and yield strength, and the strength of the wire after holding for 8 h(tensile strength of 290 MPa, yield strength of 141 MPa) was comparable with that of the wire after holding for 2 h(tensile strength of 288 MPa, yield strength of 140 MPa), the elongation ranged from 32.7% to 36.8%. In summary, 280 ℃ for 2 h was determined as the optimum annealing regime, which the tensile strength was 288 MPa, yield strength was 140 MPa, shear strength was 177 MPa and elongation was 32.4%.更多还原