Investigation of the relationship between intergranular corrosion and retrogression and reaging in the AA6063

AA6063 was heat treated with different retrogression temperatures and durations, and the effect of heat treatment conditions on the microstructure, hardness, electrical conductivity, intergranular corrosion (IGC) and electrochemical corrosion behaviours of the AA6063 was determined compared with the T6 condition. The IGC test was applied according to the BS EN ISO 11846: 2008 standard. Moreover, potentiodynamic polarization tests were applied to determine the electrochemical corrosion behaviour of the heat‐treated samples. Electrochemical corrosion tests were carried out by using a Ivium Compactstat potentiostat in 3.5 wt.%. NaCl solution at 24°C with a scanning rate of 0.5 mV/s. The corrosion test cell consisted of the reference electrode (Ag/AgCl), working electrode (test sample) and a reference electrode (platinum). The effect of IGC on the microstructure of AA6063 and corrosion depth values was investigated by using a stereo optical microscope and a light metal microscope, respectively. Corrosion depth examinations were performed on microstructures taken from the cross‐sections of the samples. The chemistry of the precipitates formed at grain boundaries and distribution of the precipitates in the microstructure were investigated by scanning electron microscope, energy dispersive X‐ray and transmission electron microscope analyses. The results showed that retrogression and reaging heat treatment improves both the corrosion resistance and the mechanical properties of AA6063. After 50°C/15 min RRA heat treatment, the highest corrosion resistance and a higher hardness value than the T6 level were obtained.     

Corrosion protection of aluminum alloy by epoxy coatings containing polyaniline modified graphene additives

In the study, polyaniline/reduced‐graphene oxide (PANI‐RGO) composites, fabricated by loading 2, 5, and 8wt% graphene oxide, was prepared by in‐situ emulsion polymerization and reduction. They are characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy. Epoxy coatings adding PANI and PANI‐RGO composites were coated on the surface of AA5083 Al alloy. The anticorrosion performance of the coatings is measured by electrochemical impedance spectroscopy and potentiodynamic polarization curve in 3.5wt% NaCl solution. The results demonstrate that the epoxy/PANI‐RGO coating exhibits a better protection against AA5083 alloy corrosion compared with the epoxy/PANI coating. Enhancement of the passivation performance of PANI was obtained by the addition of RGO into epoxy/PANI coating system.     

Corrosion Protection of AA2024-T3 by Cerium Malate and Cerium Malate-Doped Sol-Gel Coatings

Cerium malate (CeMal) was tested as a corrosion inhibitor for AA2024-T3 in this work. Corrosion inhibition on bare AA2024-T3 indicated that the inhibiting effect was a result of the synergistic effect of cerium cations and maleic anions. The corrosion of AA2024-T3 was stagnated by greatly reducing the corrosion current when CeMal was present in NaCl solutions. CeMal was adsorbed on the surface of AA2024-T3 forming a protective film in the initial stage. Then, cerium cations transformed to cerium oxide/hydroxides, precipitating on the cathode sites to inhibit the further corrosion. The electrochemical impedance spectra results of the sol-gel coatings proved that CeMal was an effective corrosion inhibitor in the sol-gel coatings to provide corrosion protection for AA2024-T3.     

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility (HTS) during solidification and improve the quality of Al alloy castings, constitutive equations for AA6111 alloys were developed using a direct finite element (FE) method. A hot tearing model was established for direct chill (DC) casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion. By applying this model to real manufacture processes, the effects of casting speed, bottom cooling, secondary cooling, and geometric variations on the HTS were revealed. The results show that the HTS of the billet increases as the speed and billet radius increase, while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases. This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation, which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.     

Study and evaluation of abrasive water jet turning process performance on AA5083

In this study, the effect of processing parameters on surface roughness and macro surface characteristics was analyzed during the machining of Ø30 mm and 300 mm aluminum alloy AA5083 abrasive water jets. As the processing parameters (up to 10 mm min⁻¹, 15 mm min⁻¹, 20 mm min⁻¹ and 25 mm min⁻¹), abrasive flow rate (50 g min⁻¹, 150 g min⁻¹, 250 g min⁻¹ and 350 g min⁻¹), the lathe chuck rotational speed (25 min⁻¹, 50 min⁻¹, 75 min⁻¹ and 100 min⁻¹) and the nozzle approach distance (2 mm, 5 mm, 8 mm and 11 mm) were used in experiments. In experimental studies, the pump pressure (360 MPa) was used as a constant, in the form of an abrasive Garnet (100 mesh), and the nozzle diameter as 0.76 mm. According to the findings, the best results in terms of surface roughness were obtained as a result of turning speed and abrasive flow rate. When the macro surface characteristics were examined, it was found that the lathe chuck rotational speed increased, the rate of nozzle progression was low, the rate of abrasive flow was high and the nozzle approach distance was lower and the smoother surfaces were obtained.     

7050铝合金表面喷丸强化层内纳米结构微观组织结构分析

利用喷丸技术在7050铝合金表面制备了纳米结构表面层。采用EBSD、TEM和XRD等方法分析了表面纳米结构层的组织结构。试验结果表明，采用喷丸技术可以在7050铝合金表面制备出纳米结构表面层，表面层是由原始晶粒细化成由表及里梯度分布的不同取向纳米级结构构成，深度～150μm。7050铝合金表面纳米化使材料的表层残余应力变成拉应力，硬度明显降低，与基体相比，表层的硬度降低了～70％。     

Numerical simulation of the effects of elastic anisotropy and grain size upon the machining of AA2024

Turning modeling and simulation of different metallic materials using the commercially available Finite Element (FE) softwares is getting prime importance because of saving of time and money in comparison to the costly experiments. Mostly, the numerical analysis of machining process considers a purely isotropic behavior of metallic materials; however, the literature shows that the elastic crystal anisotropy is present in most of the ‘so-called’ isotropic materials. In the present work, the elastic anisotropy is incorporated in the FE simulations along with the effect of grain size. A modified Johnson-Cook ductile material model based on coupled plasticity and damage evolution has been proposed to model the cutting process. The simulation results were compared with experimental data on the turning process of Aluminum alloy (AA2024). It was found that the elastic anisotropy influences the average cutting force up to 5% as compared to the isotropic models while the effect of grain size was more pronounced up to 20%.     

Study on the quality evaluation metrics for compressed spaceborne hyperspectral data

Abstract: Based on the raw data of spaceborne dispersive and interferometry imaging spectrometer, a set of quality evaluation metrics for compressed hyperspectral data is initially established in this paper. These quality evaluation metrics, which consist of four aspects including compression statistical distortion, sensor performance evaluation, data application performance and image quality, are suited to the comprehensive and systematical analysis of the impact of lossy compression in spaceborne hyperspectral remote sensing data quality. Furthermore, the evaluation results would be helpful to the selection and optimization of satellite data compression scheme.     

Effect of post-homogenisation cooling rate and Mn addition on Mg2Si precipitation and hot workability of AA6060 alloys

ABSTRACT

The microstructure evolution for different post-homogenisation cooling rates and the flow stress behaviour in direct chill cast AA6060 alloys were studied. Results revealed that decreasing cooling rates reduced the flow stress owing to the precipitation of Mg₂Si and reduction of the solid solution level. Micro-alloying of Mn generated a distribution of α-Al(FeMn)Si dispersoids during the homogenisation, with the size and number density decreasing at higher homogenisation temperatures. TEM studies confirmed that the dispersoids acted as favourable nucleation sites for Mg₂Si and significantly promoted the precipitation of Mg₂Si during subsequent cooling. The high-temperature flow stress was controlled by the solid solution levels of Mg, Si, and Mn resulting from the interaction between dispersoids and Mg₂Si. The combination of the Mn addition, a low cooling rate, and a low homogenisation temperature provided the lowest flow stress, which improved the hot workability of the alloy and promoted ready dissolution of Mg₂Si during extrusion.