The Effects of Content of Zr(NO3)4 on Formation and Characteristics of Micro-arc Oxidation Coatings Formed on ZAlSi12Cu2Mg1 Surface
The aims of this work are to prepare micro-arc oxidation coatings on the surface of ZAlSi12Cu2Mg1 aluminum alloy in Na2SiO3+NaOH+Na2EDTA electrolytes with and without Zr(NO3)4 and study their formation and characteristics. The phase constituent, surface microscopic morphology and cross-sectional morphology of the ceramic coatings were analyzed by XRD(X-ray diffraction), SEM(scanning electron microscope) and optical microscope. The thickness of the ceramic layer were measured by eddy current thickness gauge. The results show that the micro-arc oxidation films are mainly composed of mullite, α-Al2O3 and γ-Al2O3, it provides excellent adhesion with the substrate. With the content of Zr(NO3)4 in electrolyte varies from 0g/L to 1.0g/L, the thickness of the ceramic coating increases sharply at first, but afterwards reduces slowly, and the maximum of thickness up to 202μm when content of Zr(NO3)4 is 0.5g/L. The addition of Zr(NO3)4 into the base electrolyte solution is helpful in coatings formation and the coating formed in the solution containing 0.5g/L Zr(NO3)4 exhibits the best comprehensive features.
Effects of Process Parameters on Thickness and Hardness of Micro-Arc Oxidation Aluminum Oxide Ceramic Coating
The concept of oxidation power was introduced to reveal the action of energy during the micro-arc oxidation process. Thus micro-arc oxidation aluminum oxide coatings were prepared on LY12 Al alloy substrate at various process parameters using a pulse power supply. The thickness and hardness of the resulting ceramic coatings formed at fixed pulse width and frequency but varied duration and oxidation power were measured, and the changing tendencies of the thickness and hardness of the ceramic coatings with the process parameters were discussed. It was found that the hardness and thickness of the ceramic coatings tended to increase with increasing micro-arc oxidation power at fixed oxidation duration and area, while the thickness of the coating tended to increase with increasing micro-arc oxidation time and decrease with increasing workpiece area in case the other process parameters were kept constant.
Eutectic modification and microstructure development in Al–Si Alloys
Abstract Recent increasing applications for cast Al–Si alloys are particularly driven by the need for lightweighting components in the automotive sector. To improve mechanical properties, elements such as strontium, sodium and antimony can be added to modify the eutectic silicon from coarse and plate-like to fine and fibrous morphology. It is only recently being noticed that the morphological transformation resulting from eutectic modification is also accompanied by other, equally significant, but often unexpected changes. These changes can include a 10-fold increase in the eutectic grain size, redistribution of low-melting point phases and porosity as well as surface finish, consequently leading to variations in casting quality. This paper shows the state-of-the-art in understanding the mechanism of eutectic nucleation and growth in Al–Si alloys, inspecting samples, both quenched and uninterrupted, on the macro, micro and nano-scale. It shows that significant variations in eutectic nucleation and growth dynamics occur in Al–Si alloys as a function of the type and amount of modifier elements added. The key role of AlP particles in nucleating silicon is demonstrated.