Effect of Minor Er Additions on the Microstructures and Mechanical Properties of Cast Al-Cu-Mg-Ag Alloys

The microstructures and mechanical properties of novel cast Al-Cu-Mg-Ag alloys with and without minor additions of Er (0.09 and 0.2 wt %) are investigated by Vickers hardness tests, tensile tests, optical metallographic examination, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results reveal that the Er addition decreases the hardness value of peak-aged Al-Cu-Mg-Ag alloy but has little influence on the time required for achieving the peak aging condition. Meanwhile, the Ω phase is suppressed in Er-added alloys, leading to a lower tensile strength at room temperature, which causes the (Mg, Ag, Er, V, Ti)-rich phase in the matrix in Er-added alloys. This blocky phase consumes available Mg and Ag atoms for Ω nucleation, leading to the low number density of Ω plates. The strength properties of Er-added alloys at 300 °C are found to be enhanced, which benefits from the pinning effect of the Al8Cu4Er phase on grain boundaries. Meanwhile, the brittle fracture of Er-added alloys at room temperature is directly associated with the Al8Cu4Er phase and the blocky (Mg, Ag, Er, V, Ti)-rich phase, which acts as the source of microcracks during deformation. In addition, no obvious grain refinement effect can be observed in Er-added alloys.

Effect of Aging Treatment on the Corrosion Resistance Properties of 7N01 Extrusion Aluminum Alloy

The influences of non-isothermal aging (the temperature range is 150–180 °C, and the heating rate is 5 and 20 °C/h alternately), single-peak aging (aging at 120 °C for 24 h, then water quenched was followed at room temperature), and two-stage aging (aging at 105 °C for 8 h first, then increasing aging temperature to 135 °C and keeping for 12 h, followed by water quenching at room temperature) on the corrosion resistance and microstructure of the 7N01 aluminum alloy under 3.5 wt.% NaCl were investigated using electric polarization curve test and exfoliation corrosion. After aging, the hardness of samples was measured by a Vickers micro-hardness tester, and the electrical conductivities were obtained using the eddy current method. The results show that the steady phase η and metastable phase η′ are precipitated in the grain boundary of 7N01 aluminum alloy after non-isothermal aging, and their distribution is discontinuous. The hardness of the alloy can reach 136.9 HV1 and the electrical conductivity can reach 35.8% IACS, which is close to the hardness of single-peak aging and the conductivity of two-stage aging, respectively. Compared with single-peak aging, the corrosion current density of non-isothermal aging is reduced by 15.5%, and that of two-stage aging is reduced by 28.9%.

Aging Behavior of Intercritically Quenched Ductile Iron

Although extensive aging and strain aging (bake hardening, BH) studies have been carried out on dual-phase steels, the aging behavior of the dual matrix structure (DMS) ductile iron (DI), as a potential way to improve its mechanical properties, has not been addressed until now. This research was designed to study the aging behavior of DI with a ferrite-martensite matrix structure. DMS-DI with a martensite volume fraction of 30% was produced by intercritical austenitizing at 785 °C followed by quenching in water to room temperature. Aging treatments were carried out without pre-straining at aging temperatures of 140, 170, and 220 °C for 2–10,000 min. DMS-DI was investigated by light optical microscopy (LOM) for unaged samples and scanning electron microscopy (SEM) for selected samples after aging treatments. The effect of aging conditions on the mechanical properties were investigated. Microhardness measurements for ferrite and martensite were also examined as a function of aging conditions. The increase in yield strength due to aging was determined. The results indicate that the aging conditions have a small effect on the ultimate tensile strength UTS. It is shown that the yield strength increased to a maximum value of 45 MPa (~11% increase) after aging for particular time, which is found to be dependent on the aging temperature. The peak aging response is followed by a decrease in yield strength, which is observed to be attributed to martensite tempering as confirmed by microhardness measurements.

Effects of the aging state and tensile strength on the fatigue properties of 6A01 aluminum alloy

To study the effects of the aging state and tensile strength on the fatigue properties of 6A01 Al alloy, the high-cycle fatigue (HCF) experiments were carried out for different aging states. The results show that the 6A01 Al alloy with the highest tensile strength at peak-aging state can exhibit the highest fatigue strength in comparison with the overaged state and the underaged state. The main reason is that the increased strength of the 6A01 Al alloy at peak-aging state can improve the plastic deformation resistance and inhibit the fatigue crack initiation. Besides, the intermittent distribution of grain boundary precipitates at the peak-aging state is beneficial for reducing the fatigue damage. From these results, it is verified that the tensile strength plays a key role in the fatigue strength relative to the aging state for the low-strength Al alloys.

DFT and HAADF-STEM Investigations of the Zn Effects on β″ Phase Structure in a Zn Added Al-Mg-Si-Cu Alloy

First-principles calculations were conducted to investigate the effects of Zn on the structure of β″ phase. The effects of Cu, which was often added in the alloy, were also taken into consideration. Firstly, single Zn or Cu atom was doped on different sites of the β″ phase. Then the formation enthalpies and lattice constants of doped β″ phases were calculated. The results showed that it was more energetically favorable for single Zn or Cu atom to occupy Si3/Al sites than other sites. Furthermore, different quantities of Zn or Cu atoms were doped on Si3/Al sites. With the amounts of doping atoms increasing, the formation enthalpies of β″ phases doped by Zn were lower than which doped by Cu, indicating that it was more preferential for Zn to enter the β″ phase when Zn content was higher than Cu. Additionally, the doping of Zn could reduce the formation enthalpies of the β″ phase, which promoted the formation of the β″ phases. As a result, the aging hardening response of the alloy was improved. High angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) characterization was also conducted on a peak-aging Zn added Al-Mg-Si-Cu alloy. The HAADF-STEM image of β″ phase showed that the occupancies of Zn atoms were just on the Si3/Al sites and substituted all the Al atoms, which was consistent with the results of first-principles calculations.

Microstructures and Tensile Fracture Behavior of 2219 Wrought Al–Cu Alloys with Different Impurity of Fe

The Fe-rich intermetallic phases have a broadly detrimental effect on the mechanical properties of Al–Cu alloy. In this paper, the continuous evolution of Fe-rich intermetallics and their effects on mechanical properties, especially the tensile fracture behavior of 2219 wrought Al–Cu alloys as a function of Fe content against different processing approaches (i.e., as-cast, homogenization, multidirectional forging, and solution-peak aging treatment) were investigated using optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that needle-like Al7Cu2Fe or Al7Cu2(Fe, Mn) intermetallics mainly presented in the final microstructures of all alloys with various Fe contents. The size and number of Al7Cu2Fe/Al7Cu2(Fe, Mn) intermetallics increased with the increase of Fe content. The increase of Fe content had little influence on the ultimate tensile strength and yield strength, while obvious deterioration in the elongation, because fracture initiators mainly occurred at the Al7Cu2Fe/Al7Cu2(Fe, Mn) particles or particles–matrix interface. Therefore, the 2219 Al–Cu alloy with 0.2 wt.% Fe content presented relatively low tensile ductility. The tensile fracture mechanism has been discussed in detail.

Processing of high strength Mg–9Gd–3Nd–1Sn–1Zn–0.6Zr alloy by hot rolling and subsequent aging

Magnesium alloy plates can be strengthened by rolling, however, it is easy to crack or even break when the reduction of Mg–RE alloys is too large. Herein, the strengthening mechanical of the Mg–9Gd–3Nd–1Sn–1Zn– 0.6Zr alloy under different treatment conditions were investigated after hot-rolling to 80% reduction in thickness (0.8 mm) by multi-step methods. Furthermore, the rolled alloy by aging strengthening are explored. The results show that the hot-rolled alloy with 80% reduction are basically composed of dynamically recrystallized grains with the size of about 60 m, improving the mechanical properties significantly. The precipitates within grains undergo SSSS→ β″ → β′ phase transformation with the aging treatment up to 200 °C. Fine β″ precipitates were found in the grains of the rolled alloy under aged time (2 h), while β″ precipitates changed into β′ phase when the aging time was extended to 32 h. The base phase which is perpendicular to phase was precipitated in the alloy in longer aging time (96 h). In addition, the thickness of precipitates and precipitation-free zone (PFZ) at the grain boundary gradually increased as the time went on. Meanwhile, the discontinuous equilibrium phases at the grain boundary are gradually become continuous. The ultimate tensile strength and hardness were reached to 431.14 MPa, 105.9 HV at peak-aging, in addition, the elongation is reached to 3.11%, respectively. The formation of crack sources is due to the stress concentration between the brittle PFZ and the magnesium matrix, which leads to the decrease of ductility.

Effect of Retrogression Re-aging Treatment on Corrosion Behavior of 7055 Al-Zn-MG Alloy

The effect of retrogression re-aging treatment (RRA) on corrosion behavior of 7055 Al-Zn-Mg alloy were studied. Results provides the corrosion resistance could be greatly improved by RRA. After the RRA treatment, the isolated precipitates occurred on grain boundaries (GBs) and the low angle grain boundaries (LAGBs) presented a larger fraction compared to the single-stage peaking aging. The samples after RRA treatment also show better corrosion resistance than the single-stage peak aging. The results of electrochemical impedance spectroscopy (EIS) show that impedance spectrum is consisted of semi-infinite layer diffusion impedance and stagnant Weber impedance. The semi-infinite layer diffusion impedance corresponded a limited retention layer on the electrode surface. In corrosion process, Weber impedance corresponded to stagnant layer of corrosion products generated by the anode branches. The RRA sample has the high Rf and low Cf, Cp values, and the corrosion current density of the RRA samples is ten times less than the single-stage peak aging samples with the 10% hardness losing.

Effect of Cu Content on Ageing Behavior for AA3104-H19 Can Body Sheet

AA3104 ingots with different Cu content (0.1wt.%, 0.2wt.% and 0.3wt.%) were prepared by DC casting, and then the ingots were processed to 0.26mm sheets with the method of making AA3104 can be body sheet. The AA3104-H19 sheets were aged at 180°C and the aging strengthen effect were found in the 0.2wt.%Cu and 0.3wt.%Cu alloys. Optical micrograph (OM), X-ray diffraction, high resolution transmission electron microscope were used on the sheets after different ageing time. Rod like coherency precipitates with the length about 5-10nm and the thickness about 2-3nm which were parallel to the [111] plane of the matrix was precipitated at peak aging (180°C-2h). According to the result of the thermodynamic phase diagram calculation, the precipitates should be S-Al2CuMg phase, but the structure of the precipitates were different from the precipitates reported in 2XXX alloy.