Effects of Pre-stretching and Aging Treatments on Microstructure, Mechanical Properties, and Corrosion Behavior of Spray
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JMEPEG https://doi.org/10.1007/s11665-020-05142-9
Effects of Pre-stretching and Aging Treatments on Microstructure, Mechanical Properties, and Corrosion Behavior of Spray-Formed Al-Li Alloy 2195 Yongxiao Wang, Xinwu Ma, Huakun Xi, Guoqun Zhao, Xiao Xu, and Xiaoxue Chen (Submitted February 24, 2020; in revised form June 1, 2020) In this study, different pre-stretching and aging processes were applied to spray-formed Al-Cu-Li alloy 2195. The effects of different processes on the microstructures, mechanical properties, and corrosion behaviors of the alloy were examined. The strengthening and corrosion mechanisms were investigated. The samples treated with pre-stretching and aging have higher strength than the only aged samples. However, the strength is not significantly improved with the increase in the amount of pre-stretching. The prestretching treatment can suppress the formations of grain boundary precipitates (GBPs) and precipitatefree zones (PFZ), and the intergranular corrosion (IGC) sensitivity of the alloy is therefore reduced. The increase in pre-stretching promotes massive precipitation of the T1 phase, which leads to the negative shift of open-circuit potential. The over-aging treatment after pre-stretching leads to the growth of the PFZ and GBPs as well as the coarsening of the T1 phase. These changes in microstructure cause a decrease in mechanical properties and the re-sensitivity to the IGC. Under the same pre-stretching deformation, the two-step aging treatment (110 °C/12 h + 160 °C/24 h) can result in more intensive precipitation of the T1 phase, which enhanced the strength to a higher level. Meanwhile, the two-step aged alloy was immune to the IGC. The evolution mechanism of IGC for the alloy with different pre-stretching and aging processes was proposed based on the TEM characterization and the observation of IGC morphology. Keywords
Al-Cu-Li alloy, aging treatment, corrosion, mechanical property, microstructure, pre-stretching
1. Introduction In recent years, Al-Li alloys have attracted great interest in aerospace applications due to their high specific strength, specific stiffness, and low density (Ref 1, 2). This light alloy offers significant weight reduction and fuel savings for aircraft, so it can increase the aircraft capacity and range (Ref 3, 4). The problems of poor ductility and toughness in earlier generation AL-Li alloys have been solved in the new third-generation alloys by reducing Li content (about 1 wt.%) and increasing Cu content (usually more than 3 wt.%) (Ref 4, 5). The improved Al-Li alloys have been widely used as substitutes for 2000 and 7000 series aluminum alloys in the manufacture of air and space equipment (Ref 5). The third-generation Al-Li alloy 2195 is a kind of heattreatable alloy. The mechanical properties of the alloy are predominated by the precipitates in the matrix. The microstructure evolution during heat treatment and its effect on mechanical properties have been reported in recent years (Ref 6-15). Yongxiao Wang, Xinwu Ma, Guoqun Zhao, Xiao Xu, and Xiaoxue Chen
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