Xu-hu Zhang

Microstructure and mechanical properties of Mg, Ag and Zn multi-microalloyed Al–(3.2–3.8)Cu–(1.0–1.4)Li alloys

Abstract To develop super-high strength Al–Li alloy, the microstructures and mechanical properties of Mg, Ag and Zn micro-alloyed Al–(3.2–3.8)Cu–(1.0–1.4)Li alloys (mass fraction) with T8 temper were studied. The results showed that 1% of lower Li content restricted the strengthening effect of increasing Cu content, while simultaneous increase in Cu and Li contents contributed effectively to the enhancement of strength. The alloys were mainly strengthened by plenty of fine and well dispersed T1(Al2CuLi) precipitates. There were also some minor precipitates of θ ′(Al2Cu) and δ′(Al3Li), which became less in number density, even disappeared during the aging process. Meanwhile, higher Li content favored the formation θ ′ and δ ′ and a small amount of S′(Al2CuMg) phases. In addition, strengthening effect and microstructure variation were analyzed through total non-solution mole fraction of Cu and Li and their mole ratio. To obtain Al–Li alloy with super-high strength, the total mole fractions of Cu and Li should be increased, and their mole ratios should also be kept at a certain high level.

Influence of cooling rate after homogenization on microstructure and mechanical properties of aluminum alloy 7050

The influence of cooling rate (0.009–220 °C/s) after homogenization on the microstructure and mechanical properties of high strength aluminum alloy 7050 was investigated by tensile testing, optical microscope, X-ray diffraction, scanning electron microscope, and transmission electron microscope. A lower cooling rate after homogenization resulted in lower mechanical properties after aging. The drop in strength was significant when the cooling rate was decreased from 0.5 °C/s to 0.1 °C/s. A lower cooling rate gave rise to a larger amount of remnant S(Al2CuMg) phase and a higher fraction of recrystallization after solution heat treatment. Consequently, the increase in strength after aging due to precipitation hardening and substructure hardening was less significant in the case of slow cooling. This was supposed to be responsible for the lower mechanical properties due to a lower cooling rate after homogenization.

Hot deformation behavior and microstructure evolution of 1460 Al–Li alloy

Abstract The hot deformation behavior and microstructure evolution of 1460 Al–Li alloy were investigated by isothermal compression test conducted at various strain rates (10 −3 –10 s −1 ) and temperatures (573–773 K). The flow stress curves were corrected by considering the friction at the platen/specimen interface and the temperature change due to the deformation heating. The effects of strain, strain rate and temperature on the deformation behavior were characterized by the Zener–Hollomon parameter in a hyperbolic-sine equation, and the constitutive equations were established according to the peak flow stress associated with dynamic recovery, dynamic recrystallization and the dissolution of T 1 phases. In the entire strain rate and temperature range, the prediction capabilities of the developed constitutive equation are proved to be feasible and effective with a linear correlation coefficient and an average absolute relative error coefficient of 0.9909 and 6.72%, respectively.

Microstructural evolution of Mg, Ag and Zn micro-alloyed Al–Cu–Li alloy during homogenization

Abstract The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al–3.8Cu–1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, including T B (Al 7 Cu 4 Li), θ (Al 2 Cu), R (Al 5 CuLi 3 ) and S (Al 2 CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, the T B , θ, R, S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al 7 Cu 2 Fe and AlCuMn phases, and the size of Al 7 Cu 2 Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.

Effect of Zr Addition on Localized Corrosion Behavior of Al–Zn–Mg Alloy

The effects of Zr addition on localized corrosion resistance of Al–Zn–Mg alloy were investigated by means of intergranular corrosion (IGC) immersion and exfoliation corrosion (EXCO) immersion tests. The mechanism was discussed based on microstructural characterization by optical microscopy (OM) and scanning transmission electron microscopy (STEM). The results showed that Al–Zn–Mg–Zr alloy exhibited a smaller intergranular corrosion depth and exfoliation corrosion depth than Al–Zn–Mg alloy. Zr inhibited recrystallization and refines grains. The subgrain boundaries could retard the propagation of corrosion. Compared with Al–Zn–Mg alloy, Al–Zn–Mg–Zr alloy has lower Zn and Mg content of the grain boundary precipitates and narrower precipitate free zone near grain boundaries.