Haoping Peng

EFFECT OF Mg AND TEMPERATURE ON Fe–Al ALLOY LAYER IN Fe/(Zn–6%Al–x%Mg) SOLID–LIQUID DIFFUSION COUPLES

Fe/(Zn–6%Al–x%Mg) solid–liquid diffusion couples were kept at various temperatures for different periods of time to investigate the formation and growth of the Fe–Al alloy layer. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used to study the constituents and morphology of the Fe–Al alloy layer. It was found that the Fe2Al5Znx phase layer forms close to the iron sheet and the FeAl3Znx phase layer forms near the side of the melted Zn–6%Al–3%Mg in diffusion couples. When the Fe/(Zn–6%Al–3%Mg) diffusion couple is kept at 510∘C for more than 15min, a continuous Fe–Al alloy layer is formed on the interface of the diffusion couple. Among all Fe/(Zn–6%Al–x%Mg) solid–liquid diffusion couples, the Fe–Al alloy layer on the interface of the Fe/(Zn–6% Al–3% Mg) diffusion couple is the thinnest. The Fe–Al alloy layer forms only when the diffusion temperature is above 475∘. These results show that the Fe–Al alloy layer in Fe/(Zn–6%Al–x%Mg) solid–liquid diffusion couples is composed of Fe2Al5Znx and FeAl3Znx phase layers. Increasing the diffusing temperature and time period would promote the formation and growth of the Fe–Al alloy layer. When the Mg content in the Fe/(Zn–6%Al–x%Mg) diffusion couples is 3%, the growth of the Fe–Al alloy layer is inhibited. These results may explain why there is no obvious Fe–Al alloy layer formed on the interface of steel with a Zn–6%Al–3%Mg coating.

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.