Effect of quench-induced precipitation on microstructure and mechanical properties of 7085 aluminum alloy

et al. 2019

Mater. Res. Express

The time-temperature-property (TTP) and the time-temperature-transformation (TTT) curves of 7097 aluminum alloy are determined by interrupted quenching experiments in order to investigate the quench sensitivity. The quenching sensitive zone is 230°C-370°C, and the nose temperature and transformation time are about 320°C and 1.2 s, respectively. The evolution of quench-induced precipitates during different isothermal temperatures treatment has been observed by the transmission electron microscope. The number and size of quench-induced precipitates are gradually increased with the extension of isothermal holding time. Moreover, the quenching sensitivity of 7097 aluminum alloy is lower than that of 7055 aluminum alloy and 7050 aluminum alloy, but higher than that of 7085 aluminum alloy, and the influence of alloy composition on the quenching sensitivity is investigated.

Section: The Conductivity Measurement and Ttt Curvessupporting

confidence: 89%

Section: Phase Transformation Kinetics and Microstructure Evolutionsupporting

confidence: 49%

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Study on quenching sensitivity of 7097 aluminum alloy

Xie

et al. 2019

Mater. Res. Express

“…Furthermore, Chen et al [20] found that the higher Cu content leads to higher quench sensitivity in Al-Zn-Mg-Cu alloys with the same content of Zn, Mg, and other trace elements. Moreover, the effect of alloying elements on the quench sensitivity, microstructure and mechanical properties of 7085 aluminum alloy has been deeply investigated [21][22][23][24]. However, only the effect of a single alloying element or Zn/Mg ratio on the quench sensitivity of 7085 aluminum alloy has been studied and reported.…”

Section: Introductionmentioning

confidence: 99%

Investigation on the Quench Sensitivity of 7085 Aluminum Alloy with Different Contents of Main Alloying Elements

2019

Metals

The quench sensitivity of 7085 aluminum alloy with different contents of the main alloying elements (Zn, Mg and Cu) was investigated using time-temperature-transformation (TTT) curves and end quenching experiments. Then, the quenching microstructure was analyzed using transmission electron microscopy. With increasing the contents of the main alloying elements, the transitions and nose temperatures of the TTT curves are obviously increased, while the incubation time of 0.5% η (MgZn2) phase precipitation content is decreased. In addition, as the contents of the main alloying elements decrease, the conductivity of the quenched samples is increased, but the hardness of the quenched samples is decreased. Moreover, the size and area fraction of the η phase are increased with increasing the contents of the main alloying elements. Based on the experimental results, the increase of Mg and Cu contents can decrease the stability of supersaturated solid solution and increase the lattice distortion energy, which can increase the quench sensitivity of 7085 aluminum alloy.

“…Nowadays, the 7xxx series of aluminum alloys have been widely applied in the aerospace industry, profiting from their excellent combination of low density, high specific strength and high toughness [1,2]. With the rapid development of the aerospace industry and the innovation of science and technology, the demand for large-scale structural parts of high strength Al-Zn-Mg-Cu aluminum alloy is more urgent.…”

Section: Introductionmentioning

confidence: 99%

Effect of Cu on the Fracture and Exfoliation Corrosion Behavior of Al-Zn-Mg-xCu Alloy

Jiao

et al. 2018

Metals

In the present work, the influence of Cu content on microstructure, mechanical properties and exfoliation corrosion behaviors of Al-Zn-Mg-xCu alloy extrusions has been investigated in longitudinal-transverse (L-T) and short-longitudinal (S-L) directions by means of mechanical tensile and exfoliation corrosion testing combined with optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that a higher Cu content significantly decreased the fracture toughness and ductility of the alloy in S-L direction compared with L-T direction. Concomitant with the increase in Cu content, a transition in fracture mode was observed from transgranular dimpled rupture to intergranular rupture in S-L direction. Moreover, the exfoliation corrosion (EXCO) resistance of the alloy decreased as the Cu content increased and the exfoliation corrosion resistance of the alloy in short-transverse (S-T) direction was better than that of L-T direction. These results were mainly associated with the large number of coarse intermetallics caused by high Cu content in the L-T direction of alloy.Boeing 787 and Airbus A380 aircraft [5][6][7]. With the development of aerospace industry, the demand for large-sized cross-section components (especially thick plates) is becoming more and more urgent and the requirements such as hardenability and mechanical property uniformity of the alloy are also becoming stricter [8][9][10]. Wu et al.'s research showed that the anisotropy of fatigue crack propagation was ascribed to the coarse inclusion particles and T 1 precipitates [11]. Jata et al. suggested that the yield stress anisotropy may be due to the combined synergistic effect of particles and crystallographic texture [12]. Hu et al. showed that the occurrence of the anisotropy in over-aged 7050 aluminum alloy was mainly attributed to the microstructures, which were further characterized by visible precipitate free zones (PFZs) and coarse precipitates in (sub)grain boundaries [13]. However, there are few studies on the influence of alloy composition on the anisotropy of mechanical properties for Al-Zn-Mg-Cu aluminum alloy thick plate or forging, such as the Cu element. As the main alloying element of Al-Zn-Mg-Cu alloy, Cu has its solid solution strengthening effect and its addition could change the precipitation phase structure of the alloy and make the aging precipitates more dispersed and uniform, which could improve the strength and plasticity of the alloy. However, as the content of Cu increases, the alloy will have a problem of high corrosion sensitivity. Marlaud et al. observed that the precipitates were easy coarsening in the lower Cu-containing alloy due to slower diffusivity of Cu in Al compared to Mg and Zn atoms [14]. Knight et al. believed that the reduction of quenching rate contributed to the increase of Cu content in grain boundary, thereby improving the stress corrosion resistance [15]. It has also been reported that the increase of Cu content in the alloy would lead to an incre...