Microstructure control always plays a key role in enhancing properties of high-strength Al alloys. Attempts to improve the microstructure of 7000 series alloys by addition of 1.0 wt% Li have been made for a long time, but unsystematically. This article compares the microstructural features of 1.0 wt% Li-containing A1-Zn-Mg-Cu alloy with those of Li-free Al-Zn-Mg-Cu alloy by using differential scanning calorimetric （DSC） techniques, Vickers microhardness and transmission electron microscopy （TEM）. The results show the dominance of Guinier Preston （GP） zones, η＇ or η phases in 1.0 wt% Li-containing Al-Zn-Mg-Cu alloy, and confirm the capability of Li to retard the rate of precipitates growth and coarsening.
Al Zn Mg Cu系合金在较低温度时效时,形成2种类型的GP区:GP(Ⅰ)区和GP(Ⅱ)区。选用7075,7075+0.58%Li,7075+0.89%Li和7075+1.0%Li4种合金进行343K,240h和393K,24h时效,以获得GP区,并通过DSC实验结果,用Avrami Johnson Mehl(AJM)表达式计算了GP区溶解动力学参数,从而定量地研究Li对7075合金GP区转变的影响。结果表明:经过343K,240h时效后,含Li的7075合金的GP(Ⅰ)区溶解激活能较7075合金的略低,Li促进GP(Ⅰ)区的形成;经过393K,24h时效后,2种合金GP区溶解激活能相差不大。
