时效温度对SiC/Al-Zn-Mg-Cu复合材料时效析出行为的影响

Influence of Aging Temperatures on Precipitation Behaviors of SiC/Al-Zn-Mg-Cu Composites

SiC/Al-Zn-Mg-Cu复合材料力学性能的提升需要充分理解SiC颗粒的添加对Al基体时效析出行为的影响。但由于受到表征手段的限制,其内在机制尚不明确。本工作结合原位小角中子散射、透射电子显微术和拉伸实验等手段,研究了时效温度(100和160℃)对15%SiC(体积分数)增强Al-7.5Zn-1.8Mg-1.7Cu(质量分数,%)复合材料时效析出行为与沉淀强化机制的影响,并与Al-7.5Zn-1.8Mg-1.7Cu合金进行了对比。结果表明,100℃时效时,随着时效时间由0.5 h延长至3 h,复合材料中的析出相由GPI区演变为GPI区+GPII区,且尺寸明显增加。但由于该温度下时效动力学缓慢,析出相的体积分数仅略有增加。析出相尺寸和体积分数的增加均可以增大位错切过析出相的阻力,从而提升复合材料的沉淀强化能力。160℃时效温度下时效动力学加速,复合材料中析出相的尺寸和体积分数均随时效时间的延长而增加,析出相类型也由时效0.5 h的GPII区+η'相演变为时效3 h的η'相+η相。此时的沉淀强化机制以绕过型为主,尽管析出相体积分数的增加有利于提高复合材料的强度,但其尺寸的增大以及强化能力较差的平衡相η相的出现却会削弱强化效果,因此复合材料的屈服强度随时效时间的延长仅有小幅提高。与Al-7.5Zn-1.8Mg-1.7Cu合金相比,100与160℃时效3 h后复合材料的屈服强度均降低,但相关机制并不相同。100℃时效时2种材料中析出相的类型和尺寸大致相同,但复合材料由于SiC/Al界面反应消耗Mg导致析出相的体积分数减少,从而使得沉淀强化能力减弱。160℃时效时加速的时效动力学补偿了Mg消耗引起的析出相体积分数的减少,但复合材料中较低的空位浓度导致析出相粗化且平衡相η相占比增加,这也会削弱其沉淀强化能力。

A comprehensive understanding of how the addition of SiC particles influences the precipitation-strengthening behaviors of SiC/Al-Zn-Mg-Cu composites is essential for the advancement of high-performance aluminum matrix composites.However,the intrinsic mechanisms have remained unclear for a long time owing to limited characterization methods.Herein,the effect of aging temperatures(100 and 160℃)on the precipitation behaviors and strengthening mechanisms of SiC/Al-7.5Zn-1.8Mg-1.7Cu(mass fraction,%)composites containing 15%SiC(volume fraction)was investigated using in situ small angle neutron scattering,transmission electron microscopy,and tensile testing.A comparison was also made with the Al-7.5Zn-1.8Mg-1.7Cu alloy.As the aging time extended from 0.5 h to 3 h at 100℃,the precipitates in the composites evolved from GPI zones to GPI zones+GPII zones,accompanied by a noticeable increase in size.However,the increase in the volume fraction of precipitates was not substantial owing to slow aging kinetics.This increase in both the size and volume fraction of precipitates can enhance the resistance to dislocation cutting through precipitates,thereby improving the precipitationstrengthening capacity of the composites.Aging kinetics accelerated at 160℃,leading to an increase in both the size and volume fraction of precipitates in the composites with extended aging time.The types of precipitates transitioned from GPII zones+η'phase at 0.5 h toη'phase+ηphase at 3 h.Nevertheless,the primary precipitation-strengthening mechanism at this temperature was dislocation bypassing strengthening.Although the expanding volume fraction of precipitates increased the yield strength of the composites,the coarsening of precipitates and the appearance of equilibriumηphase with inferior strengthening capacity imposed limitations on the yield strength increment.Compared with the Al-7.5Zn-1.8Mg-1.7Cu alloy,the composites exhibited low yield strength after aging at 100 and 160℃for 3 h,albeit with differing mechanisms.During aging at 100℃,the type and size of precipitates in both materials were roughly the same,but the composites had a lower volume fraction of precipitates owing to Mg consumption caused by SiC/Al interface reactions,thus weakening the precipitation-strengthening capacity.Conversely,during aging at 160℃,accelerated aging kinetics compensated for the reduction in precipitates volume fraction caused by Mg consumption.However,a low vacancy concentration led to precipitate coarsening and an increased proportion of equilibriumηphase,further weakening the precipitationstrengthening capacity of the composites.