摘要
211ZX铝合金是新一代Al-Cu-Mn系耐热高强韧铝合金,为进一步提升该材料的室温成形性、力学性能和工业应用价值,通过形变热处理工艺在该合金中构筑了由超细晶、纳米晶、位错网状结构和纳米析出相组成的复合结构,使纳米薄板材的拉伸强度和塑性同时得到提高。该工艺包括固溶处理、室温多道次累积轧制变形和后续低温时效。相较于传统T6态,复合纳米结构使合金的屈服强度提升了~213 MPa,与大变形制备的211ZX铝合金纳米薄板材相比,该复合纳米结构使合金的均匀延伸率提升了~5%。通过X射线衍射仪(XRD)、激光共聚焦显微镜(CLSM)和透射电子显微镜(TEM)等微观结构表征,结合强化机制的分析,研究发现细晶强化和析出强化对具备复合结构薄板材的材料屈服强度贡献最大。借助硬度、拉伸曲线、断口截面TEM分析、位错密度及纳米析出相的演变规律分析,可以明确位错回复和高密度的纳米析出相是提升211ZX铝合金板材塑性的主要因素。
With the increasing requirements for light weight metal materials,the application of 2-series Al-Cu alloys in industry was becoming more and more extensive.211ZX aluminum alloy was a new generation of Al-Cu series alloy in dependently developed by China.In order to expand the application of the material in industry,it was necessary to improve its room temperature formability and mechanical properties.The method to improve the formability and mechanical properties of the alloy at room temperature was thermomechanical treatment,which included solution treatment,multi-pass rolling deformation at room temperature and low temperature aging.Four equal sheets of 20 mm×30 mm×5 mm were cut from the original sample.The first sheet was aged at 160℃for 10 h(T6 treatment).The second sheet was subjected to two passes of rolling deformation with a true strain of 2.04 at room temperature.After ten passes of rolling deformation with true strain of 2.04,the third and fourth sheet were aged for 30 h at 100 and 160℃,respectively.The mechanical properties of the samples were tested by hardness and tensile tests.Through X-ray diffraction(XRD),confocallaser scanning microscopy(CLSM)and transmission electron microscopy(TEM)microstructure characterization,the micro morphology and precipitation of the alloy in different states were observed respectively.Through the analysis of the microstructure and mechanical properties,the following conclusions could be drawn:(1)After the solution treated sample was deformed by two passes with a true strain of 2.04,the surface had obvious macroscopic appearance.Cracks and rolling defects,while the surface integrity of the sample after ten passes of rolling deformation was better without obvious defects.(2)In the sheet after ten-pass rolling deformation,the grains on transverse direction-normal direction(TD-ND)surface were elongated into a layered structure,and S-shaped shear bands could be observed on rolling direction-normal direction(RD-ND)surface.(3)The hardness of the rolled sheet reached its peak after aging at 100℃for 25 h.The tensile test results showed that the yield strength of the alloy in this state was 561 MPa,which was much higher than the 348 MPa in T6 state.In addition,the uniform elongation of the alloy in this state was increased by 5%compared to the deformed sample.(4)After 25 h of aging at 100℃,the dislocation density of the rolled samples decreased,forming a typical network structure.The number of nanograins increased slightly,and the size remained basically unchanged.At the same time,low-temperature aging introduced high-density nano-precipitates.(5)TEM analysis of the fracture surface after tensile test revealed that the dislocation density around the nano-precipitated phase was significantly increased.In the case of the same amount of deformation(true strain of 2.04),obvious macroscopic cracks appeared in the sheet after two-pass rolling deformation,while the integrity of the sheet after tenpass rolling deformation was better,and no obvious cracks appeared.This was because the multi-pass rolling reduced the heat of deformation,so that the copper element in the alloy existed in the aluminum matrix in the form of solid solution atoms,so there was no obvious precipitation,thereby improving the formability of the sheet.After multi-pass cumulative rolling deformation,the grains on TD-ND surface were elongated into a layered structure,and S-shaped shear bands could be observed on RD-ND surface.This was because the supersaturated solute atoms inhibited the cross-slip during the deformation process,and accelerated the accumulation of structural deformation and deformation defects inside the sheet,thereby forming an S-shaped shear band.In order to obtain a refined nanostructure,the solid solution sample was subjected to multi-pass cumulative cold rolling.The remaining T phase after solution treatment could be used as a source of dislocations to emit dislocations during the deformation process,it ccould also promote the proliferation of dislocations,or as an obstacle to accumulate dislocations.During the rolling deformation process,T phase could also reduce the mean free path of dislocation movement and promote the conversion of dislocations to other structures.Moreover,there was a certain strain gradient between T phase and the matrix during the deformation process,which was also helpful to accelerate the evolution of the structure around T phase.With the prolongation of aging time,nano-scale grains had appeared near T phase.In addition,when the low temperature aging was applied,many dislocations annihilated by meeting an opposite sign dislocation,turning the highly entangled dislocation area into a dislocation network structure.It was worth noting that the high-density dislocations near T phase form nanocrystals through severe dislocation movement(such as gliding,accumulation,and spatial rearrangement)during the aging process.The quantitative analysis of the strengthening mechanism showed that although the reduction of dislocation density reduced the contribution of dislocation enhancement to the strength,the grain boundary strengthening caused by ultra-fine grains/nanograins and the precipitation strengthening caused by high density nanocrystals eventually improved the strength of the rolled sheet.At the same time,the plasticity of the rolled sheet could be improved after low-temperature aging.This was due to the recovery of dislocations and the precipitated phases which increased the storage capacity of dislocations during the tensile deformation process,thereby increasing the plasticity of the deformed alloy.
作者
刘青青
胡德玲
杨明
李波
黄朝文
Liu Qingqing;Hu Deling;Yang Ming;Li Bo;Huang Chaowen(College of Materials and Metallurgy,Guizhou University,Guiyang 550025,China;High Performance Metal Structure Material and Manufacture Technology National Local Joint Engineering Laboratory,Guiyang 550025,China;Guizhou Electric Power Research Institute,Guiyang 550025,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2023年第7期959-966,共8页
Chinese Journal of Rare Metals
基金
贵州大学大学生创新创业训练计划项目(贵大(国)创字2019(003))
贵州省自然科学基金重点项目(ZK[2021]重点054)
贵州大学引进人才项目(贵大人基合字[2017]02)资助
关键词
211ZX铝合金
超细晶
纳米析出
力学性能
211ZX aluminum alloy
ultrafine grain
nano-precipitation
mechanical properties
