Explore the vast range of titles available.

Magnesium is the lightest structural metal, and alloying with lithium makes it even lighter. However, multi-phase Mg-Li alloys typically undergo rapid corrosion, and their strength decreases at room temperature due to natural age-softening. Here, we engineer a rapidly degrading dual-phase Mg-Li-Al alloy to be durable via friction stir processing followed by liquid CO 2 quenching. The best performing alloy has a low electrochemical degradation rate of 0.72 mg·cm −2 · day −1 , and high specific strength of 209 kN·m·kg −1 . We attribute this electrochemical and mechanical durability to its microstructure, which consists of a refined grain size of approximately 2 µm and dense nanoprecipitates. This microstructure suppressed the formation of the detrimental AlLi phase, and an aluminium-rich protective surface layer also formed. This processing route might be useful for designing lightweight and durable engineering alloys. Mg-Li alloys are attractive for their low density, yet typically suffer from limited strength and rapid corrosion. Here, both these issues are addressed in a Mg-Li-Al alloy by friction stir processing followed by liquid CO 2 quenching, resulting in a durable microstructure.

The AlSi10Mg alloy was processed by selective laser melting using both hot- and cold-build platforms. The investigation was aimed at defining suitable platform pre-heating and post-process thermal treatment strategies, taking into consideration the peculiar microstructures generated. Microstructural analyses, differential scanning calorimetry, and high-resolution diffraction from synchrotron radiation, showed that in the cold platform as-built condition, the amount of supersaturated Si was higher than in hot platform samples. The best hardness and tensile performance were achieved upon direct aging from cold platform-printed alloys. The hot platform strategy led to a loss in the aging response, since the long processing times spent at high temperature induced a substantial overaging effect, already in the as-built samples. Finally, the standard T6 temper consisting of post-process solution annealing followed by artificial aging, resulted in higher ductility but lower mechanical strength.

In this paper, we examine the effect of a small amount of Sn, Sr and Ca on the hardening and the kinetic properties of Pb. Experimentally, we analyze the specific process from the structural hardening evolution to equilibrium of PbCaSrSn alloy occurring in two steps. In the first one, a discontinuous transformation hardening and a continuous precipitation take place. A lamellar discontinuous precipitation that occurs after aging, characterizes the second step. Theoretically, we study the aging and overaging kinetics of the alloy by using the two complimentary methods needed to calculate the apparent activation energies of the Pb0.058%Ca0.12%Sr1.09%Sn associated with the various transformations, characterizing its hardening at 20 and 80 °C. We show that activation energies of aging and overaging of Pb0.058%Ca0.12%Sr1.09%Sn alloy are 25 and 28 kJ/mole, respectively, which are four times lower than the self-diffusion energy of Pb. Moreover, the addition of Ca, Sr and Sn leads to an amplification of the maximum hardness from 5 ± 5% HV to 21 ± 5% HV and an acceleration of the transformation hardening process responsible for aging.

The long production time required for large-scale parts fabricated by laser powder bed fusion (LPBF) tends to induce cracks, distortions, and overheating problems. In this work, to address these challenges, we explored and established a suitable strategy for producing large AlSi10Mg components. The platform temperatures to prevent cracks and distortions were firstly determined. Then, the in situ aging behavior was investigated for samples under various platform temperatures and holding times. Our results revealed that platform temperatures of 150°C and 200°C can effectively prevent cracks and minimize distortions. Besides, using 150°C, samples can reach peak hardness with a holding time less than 13 h. In comparison, those samples produced with a holding time longer than 13 h at 150°C and 200°C show obvious over-aging responses and thus lower hardness. However, such a hardness impoverishment can be recovered by using a T6 post-process heat-treatment.

The present study aims to evaluate plastic deformation's effect by cold-rolling on the precipitation sequence of 2024 aluminum alloy. X-ray diffraction, scanning/transmission electron microscopy, and Vickers microhardness tests have been used to characterize the microstructure and mechanical behavior of the alloys. It was observed that plastic deformation induces changes in the precipitation sequence, which affects the mechanical properties and delays the overaging stage. In the deformed alloy, two hardening peaks were observed. These peaks occurred at 30 min (248 HV ± 5) and 600 min (230 HV ± 2) and were attributed to the θ' and S' phases, respectively. However, in the non-deformed alloy, only a single hardening peak was observed. This peak arose after 300 min aging (208 HV ± 4) and was attributed to the S' phase formation. Thus, the precipitation sequence in the deformed alloy was the following: αSSS–CuMg clusters → GPB-II zones/θ''/θ'/ → S' → S, and for the non-deformed alloy was αSSS–CuMg clusters → GPB-II zones/S'/ → S.

In this study, heat treatment with varying aging durations is applied on specimens produced by selective laser melting of pre-alloyed powder of Inconel 718 alloy (IN718) to evaluate the impact of aging duration on the microstructure and corrosion resistance. A two-stage aging procedure was adopted after homogenizing the samples at 1000°C for 1 h. The aging was initially done at 740°C for 8 h then cooled to 620°C and kept for 8 h, 15 h, 25 h, and 40 h in the second stage before finally being normalized under ambient conditions. The results revealed that corrosion resistance improved significantly with longer aging durations, with the 40-h aged sample exhibiting the highest resistance. The enhanced corrosion resistance is attributed to the precipitation of γ′ and γ″ phases. Pitting corrosion resistance increased with aging duration up to 15 h in the second stage, then slightly decreased because of overaging. Similarly, hardness declined slightly beyond 25 h of aging because of the transformation of γ′ and γ″ phases into the δ phase. This study emphasizes the need for precise control of aging durations to optimize corrosion resistance and mechanical properties.

Herein, a new kind of overaging strategy: two steps of overaging for tailor rolled blank of dual phase steel (DP-TRB) was investigated. The results indicate that two steps of the overaging process is a useful way to control the mechanical properties of DP-TRB. In the premise of satisfying the requirement for the strength of DP590 grade, the total elongation can be significantly increased (3~7% in most cases). Due to the different degrees of ferrite recrystallization (differences of densities of dislocation) among the thicknesses, the obvious changes of mechanical properties among thicknesses are found. The thicknesses zones of 1.0~1.4 mm show lower strength, while the zones of 1.6~1.8 mm present higher strength. Otherwise, the high density of dislocations in samples of 1.6~1.8 mm provide more locations for Cottrell atmospheres, yield plateau occur easier. The zones with different thicknesses for one DP-TRB show two kinds of yield behaviors (continuous yield and non-continuous yield) simultaneously. The subtle C diffusion control by two step overaging leads to the quite different pinning effect of Cottrell atmospheres. Thus, the pinning effect occurs in a gradual way, and a transition state of yield behavior, which combines the characteristic of smooth curve in continuous yield and the plateau in non-continuous yield, is found.

AA 7020 alloy, widely used in the aviation and automobile industries with its specific strength, has become a material in demand in recent years by different sectors. Heat treatment to T6 temper increases the mechanical strength by precipitating hardening (ageing). Overaging to T73 temper improves the corrosion behavior of the alloy. A RRA (retrogression and re-ageing) heat treatment is a good alternative as it improves the corrosion behaviour compared to T6 temper and provides better mechanical values than precipitates from a material in T6 temper are redissolved by a short-term heat treatment between 160 and 280 °C (retrogression) which is then followed by a re-ageing under T6 heat treatment condition. In this study, the AA7020 alloy was retrogressed for 1, 5, 15, 30, and 45 minutes at 180, 200, and 240 °C. Before, it was re-ageing at 120 °C for 24 hours. The hardness, conductivity, and corrosion behaviour of the heat-treated samples were determined, and the microstructure was evaluated by light microscopy, scanning electron microscope (SEM), and Energy-dispersive x-ray spectroscopy (EDX) methods.

18% Ni maraging steels are based on the Fe-Ni-Co-Mo system with low-carbon content. They display an excellent combination of high strength and high toughness. However, they suffer from a low fatigue ratio, the ratio decreasing monotonically with increasing strength. Considering prospective applications for these steels involving fatigue loading, attempts were made by researchers to improve their fatigue life. The studies suggest that fatigue strengths higher than those realized in peak aged condition can be obtained through controlled overaging with a small amount of reversed austenite playing a critical role. Corrosion fatigue in different environments is a serious problem with these steels. Double aging seems to reduce the susceptibility to corrosion fatigue under high humidity conditions. Inclusion content has a strong influence on the fatigue life, inclusion size and type playing an important role. Surface treatments such as shot peening, laser peening, and nitriding were found to improve the fatigue life; however, it is important to optimize the process parameters. This paper attempts a critical review of studies reported in the published literature aiming to improve the fatigue life of 18% Ni maraging steels.

The mechanical properties and microstructure of Al-Cu-Li alloy sheets subjected to cryorolling (−100 °C, −190 °C) or hot rolling (400 °C) and subsequent aging at 160 °C for different times were investigated. The dynamic precipitation and dislocation characterizations were examined via transmission electron microscopy and X-ray diffraction. The grain morphologies and the fracture-surface morphologies were studied via optical microscopy and scanning electron microscopy. Samples subjected to cryorolling followed by aging exhibited relatively high dislocation densities and a large number of precipitates compared with hot-rolled samples. The samples cryorolled at −190 °C and then aged for 15 h presented the highest ultimate tensile strength (586 MPa), while the alloy processed via hot rolling followed by 10 h aging exhibited the highest uniform elongation rate (11.5%). The size of precipitates increased with the aging time, which has significant effects on the interaction mechanism between dislocations and precipitates. Bowing is the main interaction method between the deformation-induced dislocations and coarsened precipitates during tensile tests, leading to the decline of the mechanical properties of the alloy during overaging. These interesting findings can provide significant insights into the development of materials possessing both excellent strength and high ductility.