•Obtained the relationship between phase transformation of oxide scale and temperature by rapid cooling method.•Obtained the relationship between reduction process and morphology of reduced iron.•Derived the physical model at different temperatures by observing the weight loss and growth morphology of reduced iron.In order to instead of traditional acid picking method, an environmentally friendly gaseous reduction method was performed to obtain the relationship between of reduction process of oxide scale and morphology of porous iron. The isothermal hydrogen reduction of oxide scale on hot-rolled steel strip in 30 pct H2N2 atmosphere at temperature from 500 °C to 800 °C was investigated. Results show that during heating stage before reduction, the phase composition of oxide scale will transform from magnetite and magnetite/Fe eutectoid to wüstite completely. And then, the oxide scale is reduced to porous iron when temperature was below 600 °C while a dense iron layer formed on the oxide scale surface with a “minimum reduction rate” observed at 700 °C. Once the dense iron is formed, the hydrogen enters the interior of the scale along the defects and reduces the wüstite to the dense iron at the interface between the substrate and the scale. The defects (such as cracks and gaps) in oxide scale and temperature will play a vital role in the whole reduction process.

•Silicon contents of 0.5 and 1.0 wt% resulted in minimized spangle sizes, while others resulted in normal spangle sizes.•Intermetallic species of the alloy layer was described when they acted as the nucleation site in various silicon contents.•There was a decrease of phase production in FeAl3 and an increase in τ5 as silicon content increased from 0.5 to 4.0 wt%.•The interfacial binding energy of α-Al/FeAl3 is much larger than that of Al/τ5H.The effect of various silicon levels on spangle size in hot-dipped 55 wt%Al-Zn-xSi (x = 0.5, 1.0, 1.6, 2.0, 4.0, all in wt%) coatings was studied. The results showed that as silicon content was increased from 0.5 to 4.0 wt%, spangle size increased gradually from the minimized range to the normal range. Spangle range transition occurred in silicon content between 1.0 and 1.6 wt%. Correlation between intermetallic species and spangle sizes under various silicon contents was investigated. It was found that in the process of spangle size from the minimized to the normal, intermetallic species of the alloy layer were also subject to a regular change of phase transformation from FeAl3 to τ5 (also refers to α-AlFeSi), especially remarkable in the range of silicon content where spangle range transited. Phase evolution of the intermetallic layer in various silicon levels was quantitatively analyzed by thermodynamic modelling using Pandat software package, which provided a deep understanding of how the silicon content affect the formation of intermetallic species and controlled the change of intermetallic layer underneath the overlay. First-principles calculations were performed to evaluate the lattice mismatch between intermetallic species and primary α-Al, which gave an interpretation of how the intermetallic species influenced the nucleation behavior of primary α-Al during solidification and then controlled the spangle size.

•Obtained the cooling curves which close to real for 55 wt%Al-Zn-Si alloy•Calculated the latent heat of solidification by Fourier and Calphad method•Obtained and analyzed the parameters of nucleation for 55 wt%Al-Zn-Si alloy.In order to research the mechanism which grain refinement of 55 wt%Al-Zn-1.6 wt%Si alloy by Al-5 wt%Ti-0.2 wt%B (master alloy), the effect of different amount of master alloy on the microstructure and characteristic value of solidification for 55 wt%Al-Zn-1.6 wt%Si alloy were studied using thermal analysis. Important solidification events evaluated using the first and second derivative-cooling curve. The results show that the onset temperature of solidification increased from 560.1 to 572.2 °C, namely, the temperature of nucleation for primary α-Al increased from 560.1 to 572.2 °C after adding master alloy, latent heat of solidification which calculated by Fourier method increased from 168.36 to 185.61 KJ and agreed with the result of phase diagram (CALPHAD) calculation. Then, the microstructure and phase composition of cooling samples was analyzed. The results show that the microstructure was composed of primary α-Al, binary eutectic of Al-Si, ternary eutectic of Al-Zn-Si and agreed with the thermodynamic calculation.

•A nucleation model of 55 wt.%Al–Zn–1.6Si by Al–5Ti–0.2B master alloy•Comparing the stability of TiAl3 and Ti(Al,Si)3 by first principle calculation•Calculating the lattice mismatch between TiAl3 and Al matrixThe effect of Ti and Si on the nucleation of primary α-Al from the Al–43.4 wt.%Zn − 1.6 wt.%Si alloy was studied by adding Al–Ti–B to the master alloy during cooling and solidification. The effect of Si on the stability of the TiAl3/Al interface was analyzed by performing first principles calculations. The results showed that TiAl3 and the Al matrix possessed good lattice coherency, and other phases were not generated at the TiAl3/α-Al interface, according to the diffraction patterns. The interface bonding energy (vector) of TiAl3/Al decreased when Si was inserted at the Al position of the TiAl3 crystal structure, increasing the stability of the TiAl3/α-Al interface and enhancing nucleation.

First principles plane wave pseudopotential method was executed to calculate the mechanical properties with respect to the uranium-0.95 mass fraction of titanium (U-0.95 mass fraction of Ti) alloy for quenching and aging, including the elastic modulus, the value of shear modulus to bulk modulus (G/B) and the ideal tensile strength. The further research has also been done about the crack mechanism through Griffith rupture energy. These results show that the elastic moduli are 195.1 GPa for quenching orthorhombic α´ phase and 201.8 GPa for aging formed Guinier-Preston (G.P) zones, while G/B values are 0.67 and 0.56, respectively. With the phase change of uranium-titanium (U-Ti) alloy via the quenching treatment, the ideal tensile strength is diverse and distinct with different crystal orientations of the anisotropic α´ phase. Comparison of quenching and short time aging treatment, both of the strength and toughness trend to improve slightly. Further analysis about electronic density of states (DOS) in the electronic scale indicates that the strength increases continuously while toughness decreases with the aging proceeding. The equilibrium structure appears in overaging process, as a result of decomposition of metastable quenching α´ phase. Thereby the strength and toughness trend to decrease slightly. Finally, the ideal fracture energies of G.P zones and overaging structure are obtained within the framework of Griffith fracture theory, which are 4.67 J/m2 and 3.83 J/m2, respectively. These results theoretically demonstrate strengthening effect of quenching and aging heat treatment on U-Ti alloy.

The microstructure and thickness of 55 pct A1-Zn-1.6 pct Si-0.2 pct RE coatings during continuous hot-dip on Q235 steel were investigated in this work. The experimental results revealed that the intermetallic layer was composed of the Fe2Al5, FeAl3, and α-FeAlSi phases. The results of thermodynamic calculations with Pandat software package (CompuTherm, LLC, Madison, WI) indicated that FeAl3 and α(β)-FeAlSi phase precipitated during the period of temperature cooling, which was consistent with experimental result. Then, the thickness of intermetallic layer was characterized. It was shown that the thickness of intermetallic layer decreased after 0.2 wt pct RE was added. Finally, a first-principles calculation was performed to interpret the effect mechanism of RE on the thickness of intermetallic layer. The results indicated that La substitution in Fe2Al5 and FeAl3 phases could grab electronic charges from Al atoms and weaken the formation of Fe-Al compounds.

Based on Chou model and unreacted-core model, a new mixed rate controlling kinetic model has been derived in this paper to investigate the adsorption reaction time t for Mg-based hydrogen storage materials as a function of temperature T, particle radius R0 and reaction fraction ζ. This new model could be predigested into individual single step and mixed two-connection step equations. The characters of this new model have also been discussed. Moreover, the new model is successfully applied for a real case and results indicate that this new model works very well and could reasonably deal with complex kinetics mechanism.Highlights► Based on Chou model a new mixed rate controlling kinetic model has been presented. ► This new model could be predigested into single and two-connection mixed steps. ► All application results indicate our new model could treat complex kinetics mechanism.