Initial holding time dependent warm deformation and post-ageing precipitation in an AA7075-T4 aluminum alloy
Initial holding time dependent warm deformation and post-ageing precipitation in an AA7075-T4 aluminum alloy
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DOI：
10.1016/j.jmatprotec.2021.117111
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发表时间：
2021-02
影响因子：
6.3
通讯作者：
Feng Zhuangzhuang-;Chunhui Liu;P. Ma;Jianshi Yang;Chen Kailiang-;Guohui Li;Chen Longhui-;Zhibin Huang
中科院分区：
文献类型：
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作者：
Feng Zhuangzhuang-;Chunhui Liu;P. Ma;Jianshi Yang;Chen Kailiang-;Guohui Li;Chen Longhui-;Zhibin Huang
保温时间和成形温度等工艺参数是影响等温温成形性能和成形后力学性能的关键因素。通过180℃的温压模拟了AA7075-T4铝合金的等温温锻过程。采用快速加热和短期初始保温的温变形制度有利于提高高强度AA7075-T4合金的成形性，因为它降低了流动强度，显著提高了塑性。差示扫描量热仪和透射电子显微镜分析表明，在180℃保温4min的初始保温过程中，自然时效团簇迅速溶解，然后形成GP区，甚至形成Gp2相。通过在等温温变形前限制粗化析出物的生长，获得了120℃时温变形性和后续时效硬化潜力的最佳平衡，初始保持量小于30 S。温压引起的位错在后时效过程中大部分保留，加速了硬化动力学，并促进了峰值时效样品中高密度η‘/η-2析出相的形成。通过考虑AA7075-T4合金在时效初期和时效后自然时效团簇的逆转和溶质的再析出，提出了AA7075-T4合金温变形温度、初始保温时间与硬度之间的关系图。该研究不仅可以指导AA7075-T4铝合金温成形工艺的优化，而且对于建立准确的基于微观组织的AA7075-T4铝合金温变形模型也是有益的。
Process parameters such as soaking time and forming temperature are critical for the isothermal warm forming performance and post-form mechanical properties. The isothermal warm forging process of AA7075-T4 aluminum alloy has been simulated through the warm compression at 180 ℃. The warm deformation schedule including fast heating and short-term initial holding is found to be advantageous for enhancing the formability of high-strength AA7075-T4 alloy due to the reduced flow strength and significantly increased ductility. As revealed by differential scanning calorimetry and transmission electron microscopy, the natural ageing clusters quickly dissolve, then the GP zones and even η'/η2phases form during initial holding at 180 ℃ for 4 min. The optimum balance of warm-deformability and subsequent age hardening potential at 120 ℃ is obtained with an initial holding for less than 30 s, by restricting the growth of coarsening precipitates before isothermal warm deformation. The warm compression induced dislocations are largely retained during post-ageing, accelerating the hardening kinetics and promoting the formation of a high density of η'/η2precipitates in the peak-aged sample. Through considering the reversion of natural ageing clusters and solutes reprecipitation during the initial holding and post-ageing, a temperature-time-property sketch is proposed to explain the relationship between the warm deformation temperature, initial holding time and the obtained hardness for the AA7075-T4 alloy. This study could guide the optimization of warm forming process and is fruitful for establishing an accurate microstructure-based model for the warm deformation of AA7075-T4 aluminum alloy.