Hao Tu

560°C isothermal section of the Zn-Fe-Ni-Si quaternary system at the zinc-rich corner

Abstract The 560°C isothermal section of the Zn – Fe – Ni – Si quaternary system with the Zn composition being fixed at 93 at.% has been determined using optical microscopy, scanning electronic microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray diffractometry. It was found that FeSi is in equilibrium with almost all phases in the section, including the δ-Fe – Zn, FeSi2, T (Zn – Fe – Ni ternary compound), γ-Ni – Zn, NiSi2 and liquid phases. The existence of the L + FeSi + NiSi2 + γ-Ni – Zn four-phase equilibrium prevents other Ni-Si compounds from entering equilibrium with the liquid phase at 560°C. No true quaternary compound was found in the present study.

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.

600°C Isothermal Section of the Zn-Fe-Nb Ternary System at the Zn-Rich Corner

The isothermal section of the Fe-Zn-Nb ternary system at 600 oC was determined using the equilibrated alloys with the aid of diffusion couple approach. The specimens were investigated by means of SEM-EDS analysis, SEM-WDS analysis and X-ray diffraction. A true ternary phase T was identified, this phase is in equilibrium with ε, NbZn3, Γ, δ, and η - Zn phases respectively in the system. The solubility of Nb in η - Zn and δ phase is limited and that of Zn in ε is up to 10.0%.

The Hybrid Effect of Al and Cr in Zinc Bath on Galvanizing Coatings

The hybrid effect of Al and Cr in zinc bath on galvanizing coatings were studied by means of scanning electron microscope (SEM) and energy dispersive X-ray spectroscope (EDS), coupled with hot-dip galvanizing experiments. A new phase T1 was found in the coating, and the ζ phase was absent when hot-dip galvanizing at 480 °C. When Cr added zinc bath were alloyed with 0.1 wt.% Al, coating was composed of δ, ζ, η and T1 phases; when Cr added zinc bath were alloyed with 0.2 wt.% Al, δ phase layer became thinner, ζ changed from even layer to blocky crystals, and diffuse-Δ coexisted with the ζ phase. The morphology evolution of galvanizing coating was analyzed and the hybrid effect of Al and Cr were discussed with diffusion path theory.

Effect of Bismuth on the Microstructure and Corrosion Resistance of Galvanized Coating

The microstructure of the galvanized coating was investigated using scanning electron microscope equipped with energy dispersive X-ray spectroscope. The immersing and electrochemical corrosion tests were carried out to study the corrosion resistance of the galvanized coating. The addition of Bi in Zn-bath affects remarkably the morphology of the galvanized coating. The thickness of δ + ζ phase layer in the coating reaches the maximum when the content of Bi in Zn-bath is 0.5 wt.%. The corrosion resistance of the galvanized coating declines with the increase of the content of Bi.

Analysis of Morphology and Growth Kinetics of Zn-Mn and Zn-0.2wt.%Al-Mn Hot-Dip Galvanizing Coatings

The influence of manganese in Zn-Mn and Zn-0.2wt.%Al-Mn bath on the morphology and growth kinetics of the galvanizing coatings has been studied using scanning electron microscopy equipped with energy dispersive spectroscopy. When galvanized in zinc bath, the coating consists mainly h and ζphase. When manganese is added in zinc bath, the morphology of ζ phase changes from fragmental to compact. Manganese favors the formation of the δ phase and inhibits the growth of the ζ phase.When galvanized in Zn-0.2wt.%Al bath, the coating consists only δ and h phase. With the addition of manganese in Zn-0.2wt.%Al bath, the morphology of δ phase changes from fragmental to compact The thickness of the Fe-Zn intermetallic phase layer in coatings decreases obviously when manganese is added into zinc and Zn-0.2wt.%Al bath, and the thickness increases slowly with the increase of immersion time.