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Abstract：
In this research, the influence of short-term natural re-aging after T351 temper on the microstructural evolution and mechanical behavior of AA2024 aluminum alloy was investigated. Grain growth occurred in the microstructures of the natural re-aged sample and a large number of Al7Cu2Fe particles were located inside the alpha grains. At the re-aging time of 1440 min, the peaks of XRD were shifted strongly to the right due to the formation of θ\'\', S″, θ\', and S\'. The results revealed that the precipitation rate was high in the AA2024 alloy during natural aging. With increasing the re-aging time, texture parameters remained almost unchanged. The hardness increased slowly within the first 60 min, then enhanced rapidly between 60 and 2880 min, and finally became stable at around 139 HV between 2880 and 11520 min. When the natural re-aging time increased from 240 to 2880 min, the strengthening trended speed up, viz, the yield strength increased from 226.6 to 357.3 MPa, and the ultimate tensile strength enhanced from 452.2 to 535.5 MPa. Compared to the as-received sample (T351 temper), the ultimate tensile strength of the re-aged sheet improved from 455.5 to 535.5 MPa, the ductility remained unchanged, and the hardness increased from 128.8 to 138.2 HV, which was owing to the acceleration of the precipitation caused by the presence of high-content Al7Cu2Fe particles in the interior of the alpha-aluminum grains in the natural re-aged sample. It was found that the Portevin-Le Chatelier instability of AA2024 alloy was effectively postponed after natural re-aging. With increasing the natural re-aging time, the strain hardening rate of the AA2024 sheet increased. The strengthening of the natural re-aged sample for 1440 and 2880 min was a result of a synergistic effect of precipitation hardening due to the formation of θ\'\', S″, θ\', and S\' phases, elimination of Portevin Le-Chatelier instability, and highly efficient load transfer from alpha-aluminum to Al7Cu2Fe. Finally, to use the A2024 alloy produced by natural re-aging for 1440 or 2880 min, two methods were proposed.
摘要：
在这项研究中,研究了T351回火后短期自然再时效对AA2024铝合金显微组织演变和力学行为的影响。晶粒生长发生在自然再老化样品的微观结构中，大量的Al7Cu2Fe颗粒位于α晶粒内部。在1440分钟的再老化时间，由于θ\'\'的形成，XRD的峰向右强烈移动，S″,θ\',和S\'。结果表明，AA2024合金在自然时效过程中的析出率很高。随着再老化时间的增加,纹理参数几乎保持不变。硬度在最初的60分钟内缓慢增加，然后在60到2880分钟之间迅速增强，最终在2880至11520分钟之间稳定在139HV左右。当自然再老化时间从240分钟增加到2880分钟时，加强趋势加快，即,屈服强度从226.6兆帕增加到357.3兆帕，极限抗拉强度从452.2提高到535.5MPa。与收到的样品(T351回火)相比，再老化片材的极限拉伸强度从455.5MPa提高到535.5MPa，延展性保持不变，硬度从128.8HV增加到138.2HV，这是由于在自然再时效样品中的α-铝晶粒内部存在高含量的Al7Cu2Fe颗粒引起的沉淀加速。研究发现，AA2024合金的Portevin-LeChatelier不稳定性在自然再时效后被有效地推迟。随着自然再老化时间的增加,AA2024板材的应变硬化率增加。1440和2880分钟的自然再时效样品的强化是由于形成θ\'\'而产生的沉淀硬化的协同作用的结果,S″,θ\',和S'阶段，消除PortevinLe-Chatelier的不稳定性，从α-铝到Al7Cu2Fe的高效负载转移。最后,使用由1440或2880分钟自然再时效生产的A2024合金，提出了两种方法。
