Changjun Wu

Experimental investigation and thermodynamic calculation of the Zn―Al―Sb system

Abstract The 873 K isothermal section of the Zn–Al–Sb ternary system was experimentally determined using scanning electron microscopy coupled with wave and energy dispersive X-ray spectroscopy. No ternary compound was found in the present study. Based on the experiment results together with available information in the literature, the phase diagram calculation for Zn–Al–Sb was carried out by means of the CALPHAD technique. A consistent set of thermodynamic parameters for each phase was derived. The optimized results and the experimental data are in good agreement.

Experimental investigation of the Zn-Fe-V system at 450°C

Abstract Phase relations in the Zn – Co – Sb ternary system have been studied experimentally for the whole composition range, using scanning electron microscopy coupled with energy-dispersive spectrometry and X-ray diffraction. The ternary compound named CoZnSb, containing 26.0 to 36.1 at.% Co, 31.1 to 36.5 at.% Zn and 31.8 to 39.7 at.% Sb, still exists at 450 °C. Moreover, the experimental results indicate that twelve tri-phase regions could be confirmed in the system at 450 °C, and the maximum solubility of Zn in CoSb is up to 6.0at.%.

Influence of Melting Temperature and Cooling Rate on Microstructure of a Bismuth–Manganese–Iron Alloy

Effect of melting temperature and cooling rate on microstructure of bismuth–manganese–iron alloy was investigated using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy and quantitative analysis software. When bismuth–manganese–iron melt is cast in permanent mold or quenched in water, a large amount of BiMn phase form and dispersive Mn(Fe) particles exist in the alloy. The optimal melting temperature for bismuth–manganese–iron alloy is 1200°C for permanent mold casting. When the bismuth–manganese–iron alloy is melted at 1100°C and then quenched in water, the optimal water temperature is 45°C. When the liquid alloy is cooled in furnace, some Mn(Fe) particles and a lot of bismuth phase exist in bismuth–manganese–iron alloy with high manganese content. With the increase of the melting temperature, Mn(Fe) particles become coarser in bismuth–manganese–iron alloy with low manganese content. The elongation and tensile strength of the free-machining steel with 0.09 wt.%bismuth are lower than that of without bismuth.

Effect of Ti on Morphology and Growth of Zn–Fe Intermetallic Phases

The effect of Ti in Fe substrate on the morphology and growth of Zn–Fe alloy phases in (Zn–0.2 wt.%Al)/Fe diffusion couples was investigated using optical and scanning electron microscopy. It is shown that ζ phase layer does not exist in (Zn–0.2 wt.%Al)/Fe couple, but it can be clearly observed in (Zn–0.2 wt.%Al)/(Fe–Ti) diffusion couples. Increasing of dissolved Ti in Fe substrate delays the disappearance of the ζ phase and promotes the formation of δk phase. The δp phase grows toward the ζ phase layer in the form of arborescence. The growth of total intermetallic phase layers in all diffusion couples is controlled by diffusion of Zn and Fe atoms within the layers at 380 °C. The thickness of total intermetallic layer increases with increasing of dissolved Ti in Fe substrate and reaches the maximum when Ti content is 0.4 wt.%.

Microstructural Evolution and Grain Refining Efficiency of Al-10Ti Master Alloy Improved by Copper Mold Die Casting

The microstructural evolution and grain refining efficiency of sub-rapidly solidified (SRS) Al-10Ti master alloy has been studied. The results show that the mean size of Al3Ti particles in the SRS Al-10Ti master alloy decreased significantly and the morphology changed from strip-like to blocky and short rod-like compared with the conventional Al-10Ti master alloy. Grain refining experiments show that the SRS Al-10Ti master alloy is more effective than the conventional master alloy for refining Al-7Si alloy. The conversion rate of columnar to fine equiaxed grain structure in the Al-7Si alloy was promoted by the addition of SRS master alloy, and the microhardness of Al-7Si alloy increased. The mechanisms of grain refinement of aluminum by inoculation with improved Al-10Ti master alloy are discussed based on the solute theory. The decrease in size, increase in quantity, and change in morphology of Al3Ti particles are considered as the reasons for the improvement of microstructure and microhardness.

Study on Microstructure and Mechanical Properties of Hypereutectic Al–18Si Alloy Modified with Al–3B

An hypereutectic Al–18Si alloy was modified via an Al–3B master alloy. The effect of the added Al–3B and the modification temperature on the microstructure, tensile fracture morphologies, and mechanical properties of the alloy were investigated using an optical microscope, Image–Pro Plus 6.0, a scanning electron microscope, and a universal testing machine. The results show that the size of the primary Si and its fraction decreased at first, and then increased as an additional amount of Al–3B was added. When the added Al–3B reached 0.2 wt %, the fraction of the primary Si in the Al–18Si alloy decreased with an increase in temperature. Compared with the unmodified Al–18Si alloy, the tensile strength and elongation of the alloy modified at 850 °C with 0.2 wt % Al–3B increased by 25% and 81%, respectively. The tensile fracture of the modified Al–18Si alloy exhibited partial ductile fracture characteristics, but there were more areas with ductile characteristics compared with that of the unmodified Al–18Si alloy.

Study on Fe–Al layers of Fe/(Zn-11%Al-3%Mg-0.2%Si) solid–liquid diffusion couples

ABSTRACT In the present work, Fe/(Zn-11Al-3Mg-0.2Si) solid–liquid diffusion couples were held for different time periods at temperatures from 480 to 650°C to investigate the growth of Fe–Al layers. We found that FeAl3 and Fe2(Al, Si)5 phases formed on the diffusion couple interface; Si solubility in Fe2(Al, Si)5 was 1.4 at.% and the overall Fe–Al layer growth-rate time constant from 500 to 650°C ranged from 0.53 to 0.37. The layer growth rate was controlled by the inter-diffusion of Fe and Al. The overall Fe–Al layer kinetics of growth equation is . Overall Fe–Al layer thickness in the Fe/(Zn-11Al-3Mg-0.2Si) diffusion couple increased as temperature increased.

Effect of Nickel on the Microstructures of Coating in Hot-Dipped Aluminide Steel

Hot-dipping aluminizing of 45 steel was carried out in molten Al baths containing 0.0, 1.0, 3.0, and 5.0 wt.% Ni at 710°C for 10, 120, 300, and 600 s. The coatings were analyzed by x-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with energy-dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The coating hot-dipped in the Al-5Ni bath consisted of an outer Al-Ni topcoat (α-Al, θ-Al3Fe, Al3Ni, τ1-Al9FeNi), minor τ1-Al9FeNi, minor θ-Al3Fe, and major η-Al5Fe2 layers, respectively, while no τ1-Al9FeNi layer was identified in the coating hot-dipped in the Al-1Ni and Al-3Ni bath. Diffusion path model was introduced to explain this phenomenon. Ni as an alloying element added into Al bath decreased the growth rate of η-Al5Fe2 layer. The average thickness of η-Al5Fe2 layer followed the parabolic law in hot-dipping in the Al-5Ni bath. Also, η-Al5Fe2 had the largest growth rate among the intermetallic layers.

Microstructural Evolution of Aluminum Alloy 2618 During Homogenization and Its Kinetic Analysis

Abstract The microstructure evolution of aluminum alloy 2618 and its homogenization kinetics were investigated by optical microscope, scanning electron microscope, energy dispersive spectroscopy and differential scanning calorimeter. The results show that the main constituent phases in as-cast alloy 2618 are α–Al, Al9FeNi phase and non-equilibrium binary θ (Al2Cu) phase instead of typical S (Al2CuMg) phase. The θ phase was dissolved into α–Al gradually and the continuous dendritic-network structure was broken with the increase of homogenization temperature and time. DSC analysis shows that the overburnt and liquidus temperatures of as-cast alloy 2618 are 506.4 °C and 638.0 °C, respectively. After the alloy was homogenized at optimized temperature 500 °C for 16 h, the θ phase was completely dissolved in matrix. The size and morphology of Al9FeNi phase had little change, while the liquidus temperature shifted to 641 °C. The calculated homogenization time for alloy 2618 at 500 °C is 15 h, which is in accordance with that obtained in homogenization experiments.