Effects of Solution Treatment on Microstructure and High-Cycle Fatigue Properties of 7075 Aluminum Alloy

Self Cite

The fatigue performance of high-strength Al-Cu-Mg alloys is generally influenced by the process of creep age formation when applied to acquire higher strength. The results show that creep aging accelerates the precipitation process, leading to a more uniform precipitation of strengthening phases in grains, as well as narrowed precipitation-free zones (PFZ). Compared with the artificially aged alloy, the yield strength and hardness of the creep aged alloy increased, but the fatigue resistance decreased. In the low stress intensity factor region (∆K ≤ 7 MPa·m 1/2 ), the fatigue crack propagation (FCP) rate was mainly affected by the characteristics of precipitates, and the fatigue resistance noticeably decreased with the increased creep time. In a 4 h creep aged alloy, the microstructure was dominated by Cu-Mg clusters and Guinier-Preston (GP) zones, while S" phases began to precipitate in the matrix, showing better fatigue resistance. After aging for 24 h, the needle-shaped S' phases were largely precipitated and coarsened, which changed the mode of dislocation slip, reduced the reversibility of slip, and accelerated the accumulation of fatigue damage. In stable and rapid crack propagation regions, the influence of precipitates on the FCP rate was negligible.in the creep aged alloy and increase its density and uniformity, leading to a shortened time for peak aging and improved strength.The current research on creep aged alloys focuses mainly on conventional mechanical properties and less on the fatigue properties. Influenced by frequent takeoff, landing, and airflow, creep aging-formed fuselage skin, wings, and other components are the most vulnerable to fatigue failure [15]. The fatigue crack propagation (FCP) resistance of aerospace structural components is an extremely important indicator. Yin [16] and Shou [17] et al. discussed the influence of grain size on the crack growth rate of 2524 aluminum alloy. Yin suggested that within the range of low stress intensity factor ∆K, the crack closure effect of the coarse grain samples was greater than that of the fine grain samples, and the grain refinement degraded the fatigue resistance. Shou demonstrated that when the grain size was between 50 and 100 µm, the crack growth rate was relatively low, and the crack growth path became more zigzagged. Srivatsan et al. [18] studied the effect of test temperature on the high-cycle fatigue and fracture properties of AA2524, indicating that the fatigue life decreased with the increasing test temperature. Baptista et al. [19] introduced an enhanced two-parameter exponential equation model to describe the subcritical FCP behavior of 2524-T3 aluminum alloy, which performed better than other test models. However, the aforementioned studies focused on the materials without thoroughly examining the impact of the creep age forming process.Liu studied the fatigue behavior of creep aged AA2524 at 180 • C and suggested that the crack growth resistance of the alloy was reduced after treatment [20]. On the contrary, the research of Wenke...

Section: Microstructurementioning

confidence: 99%

Precipitate Evolution and Fatigue Crack Growth in Creep and Artificially Aged Aluminum Alloy

Liu

et al. 2018

Self Cite

“…The EDS analysis result shows that the stoichiometries of the lamellar eutectic phase are 81.13% Al, 7.08% Zn, 3.79% Mg, and 7.99% Cu (molar fraction), as shown in Figure 2b, which are similar to the stoichiometries of Mg(Zn,Cu,Al)2 phases. The EDS analysis result indicates that the stoichiometries of the massive eutectic phase are 78.98% Al, 1.98% Zn, 2.43% Mg, 11.19% Cu, and 5.42% Fe (molar fraction), as shown in Figure 2c, which are similar to the stoichiometries of Al7Cu2Fe phases [18]. Figure 2d-f show the microstructure and EDS spectra of Al2O3np/7075 composites at high magnification obtained under solution treatment at 480 °C for 5 h, respectively.…”

Section: Microstructure Evolutionmentioning

confidence: 55%

Effect of T6 Heat Treatment on Microstructure and Hardness of Nanosized Al2O3 Reinforced 7075 Aluminum Matrix Composites

Zhang

Yan

Liu

et al. 2019

In this study, 7075 aluminum matrix composites reinforced with 1.5 wt.% nanosized Al2O3 were fabricated by ultrasonic vibration. The effect of T6 heat treatment on both microstructure and hardness of nanosized Al2O3 reinforced 7075 (Al2O3np/7075) composites were studied via scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy, and hardness tests. The Mg(Zn,Cu,Al)2 phases gradually dissolved into the matrix under solution treatment at 480 °C for 5 h. However, the morphology and size of Al7Cu2Fe phases remained unchanged due to their high melting points. Furthermore, the slenderness strips MgZn2 phases precipitated under aging treatment at 120 °C for 24 h. Compared to as-cast composites, the hardness of the sample under T6 heat treatment was increased ~52%. The strengthening mechanisms underlying the achieved hardness of composites are revealed.

“…Al-Mg-Si-xCu alloys have been widely used in the fields of aviation, rail transportation, and the automobile industry, due to the combination of good formability and excellent corrosion resistance [1,2]; however, the relatively low strength has restricted their applications, due to the increasing requirements for larger, faster vehicles. Thus, it is necessary to develop Al-Mg-Si-xCu alloys with better mechanical properties [3,4].…”

Section: Introductionmentioning

confidence: 99%

Influences of Cu Content on the Microstructure and Strengthening Mechanisms of Al-Mg-Si-xCu Alloys

Chen

Pan

et al. 2019

The effects of the Cu content on the microstructure and strengthening mechanisms of the Al-Mg-Si-xCu alloys were systematically investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and mechanical tensile tests. The results show that, the strengthening mechanisms change with the Cu content. For as-quenched alloys, solution strengthening (σSS) is predominant when the Cu content ≥2.5 wt.%, and of equivalent importance as grain size strengthening (σH-P) when the Cu content ≤1.0 wt.%. With respect to peak-aged alloys, precipitation strengthening (σppt) is predominant when the Cu content ≥2.5 wt.%, but σSS becomes predominant when the Cu content is 4.5 wt.%. As the Cu content increases from 0.5 to 4.5 wt.%, the main type of precipitates in alloy tends to change from a β″ phase to Q′ phase, and then to a θ′ phase. Among the three types of precipitates, θ′-precipitate causes the largest increase in yield strength (σ0.2) and the largest decrease rate in elongation. β″-precipitate leads to the smallest increase in σ0.2 and the smallest decrease rate in elongation. The increase of Cu content reduces Si solubility in the Al matrix and thus decreases the nucleation rate of β″ phase during subsequent aging.