Recent advances in the metallurgy of aluminium alloys. Part I: Solidification and casting

The goal of these review papers is to summarize the recent advances in the metallurgy of aluminium alloys and from this analysis, to try to outline future developments in this field. Part I deals with the transformation of aluminium alloys from the liquid to the solid state, while Part II will focus on solid-state transformations. These papers are by no means exhaustive since the literature is very abundant, but the authors wish to give a personal view of what they think are the most relevant scientific contributions that can impact future technological developments.     

Surface temperature evolution in pulsed laser action of millisecond range

An originally developed multi-wavelength pyrometer (12 wavelengths in the range 1.001-1.573 μm, 50 μs acquisition time for each photodiode, 800 μm spatial resolution, 900-3500 °C brightness temperature range) is used to measure brightness temperature under the pulsed action of Nd:YAG laser (HAAS-HL62P) on stainless steel (INOX 304L) substrates. Specially developed “notch” filters (10⁻⁶ transparency at 1.06 μm wavelength) are applied to avoid the influence of laser radiation on temperature measurements. The true temperature is restored on the basis of method of multi-colour pyrometry. The accuracy of brightness temperature measurements is examined by comparing the temperature evolution for pulses with different durations but with the same value of energy density flux.The influence of the following parameters is studied keeping the remaining ones constant: pulse duration (6-20 ms, rectangular pulse shape), energy per pulse (10-33 J, rectangular pulse shape), pulse shape (three types of triangulars and one rectangular). Finally the evolution of surface temperature for pulses with more complex shapes but with the same pulse duration and energy per pulse is compared.     

冷却速率对液态金属Zn快速凝固过程中微观结构的影响

用分子动力学模拟方法研究了六种不同冷却速率对液态金属Zn凝固过程微观结构的影响. 采用双体分布函数g(r)曲线、平均原子总能量、Honeycutt-Andersen(HA)键型指数法和原子团类型指数法(CTIM-2)对凝固过程中微观结构的变化进行了分析. 结果表明, 冷却速率对微观结构的转变有决定性影响, 当冷却速率为1×10¹⁴、5×10¹³、2×10¹³、1×10¹³、5×10¹² K·s-1时, 系统形成以1551、1541、1431键型为主体的非晶态结构; 当冷却速率为1×10¹² K·s-1时, 系统形成以1421、1422键型为主或以密排六方(hcp)基本原子团(12 0 0 0 6 6)和面心立方(fcc)基本原子团(12 0 0 0 1 2 0)共存的部分晶态结构. 同时发现, 在形成非晶的五个系统中,玻璃化转变温度Tg随着冷速的降低而降低.     

The rheological and crystallization behavior of polyoxymethylene

In the polymer melt processing, the solidification has a huge importance on the properties of the resulting part. For a semi-crystalline resin, this phenomenon involves a complex interplay between crystallization and the material rheology. In this work, an investigation is carried out on the influence of thermal conditions on crystallization kinetics and rheology of two commercial polyoxymethylene (POM) copolymers. In particular, isothermal crystallization experiments using differential scanning calorimetry (DSC) and rotational rheometry to measure the dynamic viscosity are performed. The evolution of the relative crystallinity and Normalized Rheological Function (NRF) are correlated by a recent technique which allows simultaneous analysis of several measurements, even if they are not carried out at same temperatures. On this basis, a relationship between the crystallinity and the hardening, i.e. the sharp increase in the viscosity, is obtained.     

Modulating the rheological response of shear thickening fluids by variation in molecular weight of carrier fluid and its correlation with impact resistance of treated p-aramid fabrics

The present study deals with the effect of molecular weight of carrier fluid on the rheological behaviour of shear thickening fluid (STF) and impact energy absorption by treated p-aramid fabrics. High molecular weight polyethylene glycols (HMW-PEG: 1000, 3000 and 6000 g mol⁻¹) were individually added to a mixture of PEG 200 and PEG 600 to prepare ternary mixtures of carrier fluids. Increase in average molecular weight of the carrier fluid via addition of PEG 1000 and PEG 3000 enhanced the dilatant behaviour of STF. On the other hand, addition of PEG 6000 led to a rheological response inferior to that obtained via addition of PEG 3000 owing to solidification of the former at room temperature resulting in fusion of silica particles. However, an inverse relation was observed between the rheological behaviour of HMW-PEG based STFs and impact resistance of p-aramid fabrics treated with them. The diminution in impact energy absorption occurred due to lubrication effect caused by long polymer chains of HMW-PEG. On the other hand, fusion of solidified PEG 6000 and silica particles created rough microstructures over the yarn surface, which enhanced inter-yarn friction, resulting in improved impact energy absorption.     

Effect of ultrasonic melt processing and Al-Ti-B on the microstructural refinement of recycled Al alloys

Refining the α-Al grain size and controlling the morphology of intermetallic phases during solidification of Al alloys using ultrasonic melt processing (USMP) and Al-Ti-B have been extensively used in academic and industry. While, their synergy effect on the formation of these phases has not yet clearly demonstrated. In this paper, the influence of USMP and Al-Ti-B on the solidified microstructure of multicomponent Al-4.5Cu-0.5Mn-0.5Mg-0.2Si-xFe alloys (x = 0.7, and 1.2 wt%) has been comparatively studied. The results show that the USMP + Al-Ti-B method produce a more profound refinement effect than the individual methods. In addition, the area of single Fe-rich phases in both alloys with USMP + Al-Ti-B are also refined compared with conventional methods. A mechanism is proposed for the refinement, which are the deagglomerated TiB₂ parties induced by USMP providing more effective nucleation sites for α-Al, and the refined interdendritic regions limited the growth of Fe-rich phases in the following eutectic reaction. Finally, the application of combined USMP + Al-Ti-B methods is feasible in microstructural refinement, resulting in the improving the casting soundness and mechanical properties of alloys.     

Development of continuous hydrothermal hot-pressing apparatus

Abstract

A process for continuous hydrothermal hot-pressing has been examined, with the resultant development of a new continuous hydrothermal hot-pressing apparatus. In this study, amorphous siliceous material, slaked lime and pulp fiber were mixed and solidified, at 200°C, to produce a board product. The duration of the hydrothermal hot pressing reaction process was 17 minutes. The bending strength of the board product was high; 11MPa.     

Phase diagram features and solidification behaviour of CoCu2O3 at elevated oxygen pressure

A unique behaviour of the phase CoCu₂O₃ was found both from CALPHAD calculations and directional solidification experiments. For elevated oxygen partial pressure the solidification mode changed from double-peritectic to a congruent melting behaviour with respect to the metals (Cu, Co) and to the oxygen content. This transition predicted by the phase diagram calculations was confirmed by microstructure and phase analyses of samples solidified at oxygen pressures up to 60 bar. A DTA analysis has verified basic features of the phase diagram at normal pressures.     

Determination of haloperidol in biological samples with the aid of ultrasound‐assisted emulsification microextraction followed by HPLC‐DAD

A rapid and simple quantitative method for preconcentration and determination of haloperidol in biological samples was developed using ultrasound‐assisted emulsification microextraction, based on the solidification of floating organic droplet combined with HPLC‐DAD. The effects of several factors were investigated. A total of 30 μL of 1‐undecanol as an extraction solvent was injected slowly into a glass‐centrifuge tube containing 4 mL alkaline sample solution that was located inside the ultrasonic water bath. The formed emulsion was centrifuged and the fine droplets of solvent were floated at the top of the test tube, then it was cooled in an ice bath and the solidified solvent was transferred into a conical vial, after melt, the analysis of the extract was carried out by HPLC. Under the optimal conditions, the extraction efficiencies were more than 90% and the preconcentration factors were obtained between 119–122. The LOQs were obtained between 4–8 μg/L and the calibration curves were linear within the range of 4–1000 μg/L. Finally this method was applied to the determination of haloperidol in plasma and urine samples in the range of μg/L and satisfactory results were achieved (RSDs <7%).