摘要
Grain growth of nanostructured Al6061produced by cryorolling and aging process was investigated during isothermalheat treatment in100?500°C temperature range.Transmission electron microscopy(TEM)observations demonstrate that aftercryorolling and aging at130°C for30h,the microstructure contains61nm grains with dispersed50?150nm precipitates and0.248%lattice strain.In addition,an increase in tensile strength up to362MPa because of formation of fine strengtheningprecipitation and nano-sized grains was observed.Thermal stability investigation within100?500°C temperature range showedrelease of lattice strain,dissolution of precipitates and grain growth.According to the X-ray diffraction(XRD)analysis,Mg2Siprecipitates disappeared after annealing at temperatures higher than300°C.According to the results,due to the limited grain growthup to200°C,there would be little decrease in mechanical properties,but within300?500°C range,the grain growth,dissolution ofstrengthening precipitates and decrease in mechanical properties are remarkable.The activation energies for grain growth werecalculated to be203.3kJ/mol for annealing at100?200°C and166.34kJ/mol for annealing at300?500°C.The effect ofprecipitation dissolution on Al lattice parameter,displacement of Al6061(111)XRD peak and Portevin?LeChatelier(PLC)effect onstress?strain curves is also discussed.
研究深冷轧制时效态纳米6061铝合金在100~500°C下等温热处理过程的晶粒生长。透射电子显微镜观察结果表明经深冷轧制及在130°C时效30 h,合金显微组织中含有61 nm的晶粒和50~150 nm的析出相,以及0.248%的点阵畸变。此外,由于形成细小的强化相和纳米晶粒,合金的拉伸强度达到362 MPa。在100~500°C下进行热稳定研究,结果表明,点阵畸变得到减弱,析出相溶解,晶粒长大。X射线衍射结果表明,当退火温度高于300°C时,Mg2Si相将消失。当退火温度低于200°C时,晶粒长大不明显,力学性能下降也不明显。但在300~500°C时,晶粒长大,析出相溶解和力学性能下降都比较明显。在100~200°C时,晶粒长大的活化能为203.3 k J/mol,在300~500°C时,活化能为166.34 k J/mol。讨论了析出相溶解对铝点阵常数和XRD(111)面峰位位移的影响,也讨论了PLC对应力应变曲线的影响。
