The Degree of Rust Remaining on the Surface of Ball-milled Steel Parts and Its Effect on the Leakage of Hot-dip Galvanizing

Batch hot-dip galvanizing is a mature corrosion protection method. However, the waste acid and gas generated in the pretreatment seriously pollute the environment, which urgently requires the development of an environmentally friendly hot-dip galvanizing. Ball-milling is a promising surface treatment method. The use of ball-milling instead of pickling in the traditional hot-dip galvanizing can avoid the generation of waste acid and meet the sustainable development requirements of green environmental protection The iron ingot samples (20 mm x 20 mm x 3 mm) were used as the raw material Before hot-dip galvanizing, the samples were alkaline washed in 15wt.% NaOH solution at 70-90 ℃ for 3 min to remove surface grease. Then, at room temperature, the surface oxides were removed by pickling or ball-milling. Pickling is to soak the alkali-washed sample in a 10wt.%-15wt.% hydrochloric acid solution for 3 min. Ball-milling is to put the alkali-washed samples together with 304 stainless steel grinding balls into a ball mill with a diameter of 60 mm, and remove the oxides on the surface of the samples through the mechanical action of the grinding balls. Based on theoretical calculations, the ball-milling parameters designed: the particle size of the grinding ball d = 2 mm, 5 mm, 8 mm; the rotational speed of the drum r=120 r/min, 130 r/min, 140 r/min, 150 r/min; the filling factor of the grinding ball is 0.5. The rust-removed samples were rinsed in deionized water and then fluxed. The NH4Cl-ZnCl2 solution (1.2∶1) with a concentration of 200-300 g/L using as the fluxing agent, the temperature was (75±5) ℃, and the time was 5 min. Then the samples were immediately dipped in the zinc bath after being dried in a blast drying oven at 100 °C for 10 min. The composition of the zinc bath is 99.9wt.% pure zinc, the mass is 2 kg, the temperature is (450±3) ℃, and the time is 60 s. The hot-dipped workpiece is slowly lifted out of the zinc bath, and then immediately quenched in water Optical Microscope was used to observe the effect of ball-milling parameters on the residual rust degree of the steel surface. With the increase of the particle size of the grinding ball, the residual rust degree α on the steel surface reduces to 0. Scanning Electron Microscope and High-temperature Pendant Drop Contact Angle Measuring Instrument were used to analyze the effect of residual rust degree of steel surface on hot-dip galvanizing leakage. With the decrease of the residual rust degree, the contact angle between the zinc droplet and the matrix decreases, and the wettability improves. When the residual rust degree reaches 0, the contact angle θ=84°, and the zinc liquid spreads evenly on the substrate surface, which can avoid the leakage of the coating and achieve the same effect as pickling.

Effect of ball-milling pretreatment on microstructure and corrosion of hot-dip galvanized coating

Synergy of ball-milling and pre-oxidation on microstructure and corrosion resistance of hot-dip zinc coating of nodular cast iron

The Influence of Al on the Surface Properties of the Hot-dip Galvanized Melt

Wettability of Zn-Al alloy melt on the pure iron substrate at 450 °C was studied. The effect of Al content (Zn, Zn-1Al, Zn-2Al, Zn-3Al, Zn-4Al, and Zn-5Al) on the wetting behavior and interfacial reaction was investigated by high-temperature contact angle measuring device and scanning electron microscope (SEM). The results show that, with the increase of Al content, the initial contact angle of the molten alloy on the substrate decreases gradually and the wettability increases gradually. Compared with the initial contact angle, the final contact angle is slightly reduced, because the Fe-Al inhibition layer is preferentially formed at the interface when adding Al to the alloy. The presence of Al will promote the occurrence of the reactive wetting, leading to an insignificant wetting spreading process, and the final contact angle negligibly differs from the initial contact angle. The adhesion work and charge density distributions of interface systems were calculated based on the first-principles. The results show that the adhesion work of the Fe/Zn and Fe/(Zn-Al) interface model is 2.017 1 J/m2 and 13.794 4 J/m2, respectively. The addition of Al greatly increases the adhesion work between alloy melt and iron substrate. Compared with the Zn-Fe and Al-Fe interface models, it can be seen that a significant charge migration phenomenon occurs between the interfaces. The amount of charge migration in the Al-Fe interface model is much larger than that in the Zn-Fe interface model, indicating that the bonding between Al-Fe atoms can occur more easily and the interaction between Al-Fe interfaces is stronger. This is also the reason why the addition of Al increases the adhesion work between interfaces.

Effect of Antimony on Wetting Behavior and Interfacial Reaction between Zinc Liquid and X80 Steel

The wetting behavior of molten Zn and Zn-Sb alloy and X80 steel in a high vacuum environment was studied by the modified sessile drop method. The wetting morphology and interface structure were analyzed by scanning electron microscope and energy dispersive spectrometer. The results show when the content of Sb in Zn-Sb alloy increases from 0.0 wt. % to 1.0 wt. %, the initial contact angle between the droplet and the substrate decreases from 102.8° to 82.5°, and the equilibrium contact angle also decreases from 57.4° to 41.4°. Sb element in the Zn-Sb alloy can reduce the contact angle and improve the wettability due to its smaller surface tension. The spreading process of Zn-Sb alloys on X80 steel can be divided into rapid adsorption, reaction control, steady-state equilibrium stages, and Zn-Sb alloys with different mass fractions have the same spreading kinetics. The volatilized Zn element in the Zn-Sb alloy will reduce the oxide film on the surface of the substrate, making it easier for the Zn-Sb droplet to wet the steel plate and induce the formation of a precursor film. The formation mechanism of the precursor film is the subcutaneous penetration mechanism.

Effect of Surface Micromorphology and Roughness of Iron Ingot on Microstructures of Hot-Dip Galvanized Coating

Microstructure and mechanical properties of Al–Si alloy modified with Al–3P

The 600 °C Isothermal Section of the Al-Cu-Ti Ternary System