Al–Si–Mg cast alloys can be imparted with a wide range of mechanical properties through heat treatment, thus meeting the required performance of various vehicle components. However, because of the ...characteristics of the high-pressure die casting process, the gas porosities in the casting can lead to blisters during the solution treatment of die-casting parts. Therefore, systematic studies on the solution temperature and solution time are required to prevent such blisters. In this study, the gas porosity and mechanical properties of T6 heat-treated specimens were evaluated under various solution treatment conditions. As the solution treatment temperature and time increased, the numbers and volume of individual gas porosity increased. On the other hand, there were little changes in the shrinkages upon heat treatment. As solution temperature and time increased, the area fraction of the eutectic Si particles and Mg2Si decreased slightly, whereas the area and sphericity of the eutectic Si and Mg2Si increased. As the solution treatment temperature and time increased, the ultimate tensile strength and yield strength increased, whereas the elongation tended to decrease. However, the maximum UTS and YS were obtained on treatment at 520 °C for 1.5 h.
•Vacuum die casting of Al–Si–Mg alloy under solution treatment conditions.•Separation of gas porosities and shrinkage and their quantitative measurement.•Mechanical property comparison between T6 heat-treated and as-cast specimens.
The 7xxx series alloys are heat treatable wrought aluminium alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. ...Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effects of homogenisation, solution treatment, quenching and ageing treatments on the evolution of the microstructure and properties of some important medium to high-strength 7xxx alloys. With a focus on recent work at Monash University, where the whole processing route from homogenisation to final ageing has been studied for thick plate products, it is reported how microstructural features such as dispersoids, coarse constituent particles, fine-scale precipitates, grain structure and grain boundary characteristics can be controlled by heat treatment to achieve improved microstructure–property combinations. In particular, the paper presents methods for dissolving unwanted coarse constituent particles by controlled high-temperature treatments, quench sensitivity evaluations based on a systematic study of continuous cooling precipitation behaviour, and ageing investigations of one-, two- and three-step ageing treatments using experimental and modelling approaches. In each case, the effects on both the microstructure and the resulting properties are discussed.
The simple assembling process and lower manufacturing cost are crucial for wide application of perovskite solar cells. In this work, we report an efficient interface passivation strategy for ...preparing high-performance planar perovskite solar cells, which does not require well-controlled moisture and oxygen atmosphere. A NH4F solution-based additive is introduced to passivated TiO2 electron transfer layer, which offers reduction of oxygen-induced defects and residual surface hydroxyl groups, and lower trap state level. Using a typical planar structure of FTO/NH4F-TiO2/CH3NH3PbI3/Spiro-OMeTAD/Au, the champion device achieves a power conversion efficiency of 15.61%. After 28-day durability test, the device with NH4F-treated TiO2 storing in air without any encapsulation exhibits a little efficiency loss (<10%). Our work demonstrates a generic approach to develop air-processed efficient planar perovskite solar cells by interface engineering for future commercialization.
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•A NH4F additive is introduced to passivated TiO2 electron transfer layer.•The oxygen-induced defects and residual hydroxyls at interface are suppressed.•The air-processed device achieves a power conversion efficiency of 15.61%.•The NH4F-treated device storing in air exhibits a little efficiency loss.
The dense 2219 Al alloy was successfully fabricated by the Wire + Arc additive manufacturing (WAAM) technology. It was subsequently processed through solution and aging (T6) heat treatment to improve ...its performance. There were some θ' phase precipitated because of the thermal cycling during the WAAM forming process. Then, the supersaturation of copper in the α-Al matrix was reduced. The influence of solution temperature on the precipitation behavior of the θ″ phase and the microstructure evolution were investigated in detail. The experimental and calculative results demonstrate that the precipitation strengthening of the θ″ phase improves with the increasing solution temperature, and the strengthening contribution of θ″ phase is 202.1 MPa, 165.2 MPa, and 150.3 MPa corresponding to the solution temperature at 540 °C, 530 °C, and 520 °C, respectively. The average ultimate tensile strength, yield strength, elongation, and micro-hardness of the WAAM processed samples were obtained after T6 treatment with 540 °C, 45 min/Water quenching +180 °C, 6 h/Water quenching, which is 397 ± 4 MPa, 303 ± 5 MPa, 5.3 ± 1%, and 139 ± 6 HV respectively. Compared to the casting + T6 treated 2219 Al alloy, the samples in this research present a similar tensile strength and slightly lower ductility.
•θ' phase precipitates due to the thermal cycle in the WAAMed 2219Al.•The supersaturation of copper in Al affects the precipitation strengthening in WAAMed 2219Al.•The higher solution temperature (<540°C) leads to largerleads to increment of yield strength.
Cast Al–Mg alloys with high Mg content have attracted considerable interest as a result of exceptionally low mass density and enhanced Mg solid-solution strengthening effect. However, poor ductility ...in this class of cast Al–Mg alloys originating from the increased amount of brittle Al3Mg2 phase presents a challenge. This work aims to improve ductility of a cast Al-10 wt%Mg alloy by prolonging time and/or increasing temperature during solid-solution treatment, hence minimizing the amount of the Al3Mg2 phase. The amounts of Al3Mg2 decrease and the concentrations of solute Mg increase with prolonging time and/or increasing temperature, improving both ductility and strength. Solid-solution treatment at 425 °C for 9 h or at 438 °C for 3 h induces complete dissolution of the Al3Mg2 phase, achieving an average uniform elongation of ~27% accompanied by an average 0.2% offset yield strength of ~186 MPa. The mechanisms improving both ductility and strength are discussed.
Diverse microstructure and complex application environments increases the uncertainty of the corrosion resistance of lightweight steels. The effect of solution treatment on the corrosion behavior of ...Fe–16Mn–10Al–1.5C–0.1Ti lightweight steel in Cl−, HSO3− and Cl−–HSO3− environments was investigated using electrochemical measurement, scanning electron microscope (SEM) and X–ray photoelectron spectroscopy (XPS). The lightweight steels are dominated by austenite and contain a small amount of ferrite. The increase in solution treatment temperature leads to more ferrite formation, but it has less effect on grain size. The decrease in austenite content results in more corrosion microcells and a porous oxide film; therefore, the corrosion resistance of the steel deteriorates with increasing temperature. In addition, in the Cl−–HSO3− environment, the synergistic effect of Cl− and HSO3− leads to the formation of a weak protective oxide film, resulting in a significant increase in corrosion rate compared to the Cl−and HSO3− environment.
The influence of Erbium (Er) addition and thermal treatments on the microstructure and hardness of Al-0.5 wt.%Mg-1.0 wt.%Si alloy has been studied. Chemical composition of the alloys was measured by ...optical emission spectrometry (OES) and x-ray fluorescence (XRF). Microstructural evolution of as-cast, solution-treated, and aged samples were characterized by scanning electron microscope (SEM). The phase identification and elemental distribution were obtained from energy dispersive spectroscopy (EDS). From the microstructure, it was confirmed that solutionization at 570 ͦ C for 15 hours dissolved the Mg2Si and Er-rich intermetallics. However, some Fe-rich intermetallics remained after the solution heat treatment. Er addition had a role on the modification of β-AlFeSi and improved the hardness. Er-modified Al-Mg-Si alloy gave a significant improvement in mechanical properties. Therefore, Er is one of the candidate elements that could provide an opportunity for a high-strength Al-Mg-Si alloy.
With the development of nickel-based single crystal superalloys, the quantity of micro-pores generating in solution treatment has increased, and there is an urgent need to develop a solution ...treatment design method that takes account of both residual eutectics and micro-pores. Therefore, the effect of heating processing on the formation of micro-pores during solution treatment of a 4th generation nickel-based single crystal superalloy has been investigated using high-resolution transmission X-ray tomography and electron probe microscopic analyzer. In the temperature range below interdendritic γ' phases solvus, decreasing the heating rate can limit the formation of micro-pores significantly. However, heating method (continuous or stepwise), has a little effect on micro-pores formation. The influence of heating processing on micro-pores formation is associated with composition homogenization degree of the alloy before eutectics dissolve. Moreover, it is found that the dissolution of eutectics is most likely the reason for substantial formation of micro-pores. Finally, a designing thinking for heating processing of solution treatment for high generation nickel-based single crystal superalloys is proposed.
•Transmission X-ray tomography technique was used to characterize the micro-pores.•Severe Kirkendall effect during eutectic dissolution causes formation of H-pores.•Decreasing of heating rate can limit the formation of H-pores significantly.•Heating method of solution treatment has a little effect on H-pores formation.
Owing to their unique microstructure, GH3230 superalloys prepared using laser powder bed fusion (LPBF) exhibit high strength but low ductility, which limits their functional performance in engine ...combustion chambers. In this study, the process parameters were optimized to obtain LPBF GH3230 with minimal defects, and solid-solution treatment (ST) was conducted to modulate its inhomogeneous microstructure and mechanical properties. The results revealed that ST eliminated the substructure of as-printed (AP) samples and transformed nano-M23C6 into micron and submicron M6C/M12C in situ. Significant amounts of M6C/M12C promoted Orowan strengthening, but the quasi-continuous semi-coherent lattice interface between M6C/M12C and the matrix was a weak zone for cracking, resulting in reduced plasticity owing to the presence of micron carbide. The increased solid solution temperature causes the carbide to remelt, triggering a strong plastic transformation. The impact of carbide size on strength and plasticity conversion rate was more significant than that of carbide content. Final, LPBF-GH3230 samples containing micron carbides were obtained in ST below 1230 °C with an ultimate tensile strength (UTS) comparable to that of forgings. Further increase in the ST temperature to 1280 °C eliminated the carbides, a LPBF-GH3230 that fulfilled the strength standard for cast parts (647 ± 23 MPa) with an excellent elongation (39.4 ± 1.7%) was obtained. This study provides a theoretical basis for the practical application of the LPBF GH3230 superalloy in the aerospace industry and offers guidance for improving post-treatment methods to ensure high plasticity.
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•M23C6 served as nucleation sites for M6C/M12C during solid-solution treatment.•Original uneven segregation led to the bimodal size distribution of carbides.•Superalloy plasticity was regulated by controlling the carbide size and content.•Micron carbide size had a greater effect on ductility than did the carbide content.•Superalloys with excellent performance comparable to that of castings were obtained.
