M. Sakairi

Behavior of Second-Phase Particles in Al5052 Alloy during Anodizing in a Sulfuric Acid Solution CSLM Observation

The behavior of second-phase particles during anodizing of Al5052 alloy in 16 wt% sulfuric acid solution was investigated by confocal scanning laser microscopy (CSLM). Two different types of second-phase particles were observed in the Al5052 ailoy, Al-Mg particles and Al-Mg-Fe particles. The Al-Mg particles showed a groove-type morphology because of selective dissolution of Mg during anodizing, while Al-Mg-Fe particles showed a protrusion-type morphology in the CSLM height image (top view). The CSLM contrast image of cross sections of the anodic oxide film showed the presence of two different types of imperfections in the anodic oxide film, bright- and dark-type imperfections. The bright-type imperfections were determined to contain metallic iron, indicating that the metallic iron had been transferred from the substrate into the oxide film without oxidation during anodizing: this reflects the incident laser beam strongly to give a bright CSLM contrast image. The dark-type imperfections were explained by a scattering of the laser beam with vacant or irregularly structured regions, resulting flrom the selective dissolution of Mg.

Three-dimensional microstructure fabrication with aluminum anodizing. Laser irradiation, and electrodeposition

Three-dimensional microstructures made of Ni metal or acrylic resin were fabricated by five sequential processes: porous anodic oxide film formation, pore scaling, laser irradiation, Ni electroplating or electrophoretic deposition of acrylic resin, and removal of the aluminum substrate and anodic oxide films. Cylindrical and prismatic aluminum rods were anodized in an oxalic acid solution to form porous-type anodic oxide films, and then immersed in boiling distilled water for pore sealing. The anodized and pore-sealed specimens were irradiated with a pulsed neodymium-doped yttrium aluminum garnet (Nd-YAG) laser beam in a Ni plating solution or doubly distilled water to remove anodic oxide film locally by rotating and moving up/down with an XYZθ stage. Nickel or acrylic resin was deposited at the area where film had been removed by cathodic or anodic polarization in the solution before removing the aluminum substrate and anodic oxide films in NaOH solutions. Cylindrical and prismatic network cages, rings, springs, and bellows made of Ni metal or acrylic acid resin were fabricated successfully.

Fabrication of Micropores and Grooves on Aluminum by Laser Irradiation and Electrochemical Technique

Micropores and microgrooves were fabricated on aluminum specimens using anodizing, laser irradiation, and electrochemical techniques. In the fabrication of the micropores, aluminum specimens covered with anodic oxide film were irradiated with a pulsed Nd yttrium aluminum garnet laser (i) on open circuit or (ii) under anodic polarization in NaCI solution. The laser irradiation caused the formation of cone-shaped pores, while the laser irradiation under anodic polarization caused the formation of hemispherical pores. In the fabrication of microgrooves, successive procedures of anodizing, laser irradiation, reanodizing at the laser-irradiated area, and stripping of oxide film were carried out. Microgrooves with a 30 μm linewidth and 20 μm depth were obtained.

Laser‐Assisted Electroless Ni‐P Deposition at Selected Areas on Al (‐Mg, Si, Cu) Alloys

Local deposition of Ni-P alloys on highly pure aluminum, commercially pure aluminum, Al-Cu-Mn, Al-Mg, and Al-Si-Mg alloys was attempted by anodizing, laser irradiation, and electroless plating. Specimens were first anodized at 15 V in 16% H 2 SO 4 , and then irradiated with a pulsed Nd-yttrium-aluminum-garnet laser in a Ni 2+ /H 2 PO 2 - solution. Nickel-phosphorous electroless plating was finally carried out in a Ni 2+ /H 2 PO 2 solution with 0.6 ppm of Pb 2+ ions. The effect of alloying elements on the Ni-P deposition during electroless plating was investigated. Anodic oxide films on all the specimens were sufficiently stable in Ni-P electroless plating solution and able to ensure local deposition of Ni-P only at the laser-irradiated areas. The deposition rate of Ni-P on all the aluminum alloy specimens was higher than that on highly pure aluminum. The effect of the alloying elements on the Ni-P deposition in electroless plating is discussed in terms of the catalytic function in Ni-P electroless deposition and the inhibition of the oxide film formation during laser irradiation.

Application of CSLM to the Surface Morphological Study of Al 5052 Alloy Anodized in Sulfuric Acid Solution

Confocal scanning laser microscopy (CSLM) was applied to the surface morphological study of the anodic oxide film-covered A15052 alloy. Contrast and height images of the specimens were obtained by scanning the laser beam in the x, y, and z directions. The incident laser beam appeared to be reflected by either the outer oxide surface, imperfections in the oxide film, or the inner oxide/metal interface. Contrast images of the outer oxide surface and the metal/oxide interface were obtained separately by choosing different scanning ranges of the focused z point of the incident laser beam. Two different types of imperfections, bright and dark, were observed in the contrast images of CSLM. The bright imperfections may correspond to inclusions with high reflectivity, and the dark ones to inclusions with uneven surfaces. The z position of the bright imperfections in the oxide film was determined by analyzing the height images.

Effect of Aspect Ratio of Artificial Pits Formed on Anodized Al by PRM on Localized Corrosion in Chloride Environments

New in solution type artificial pit formation with area selective electrochemical measurement technique was established. Artificial pits were formed on anodized 1070 aluminum in solutions by continuous focused pulse YAG laser beam irradiation. The aspect ratio (pit depth/pit width) of formed pit can be changed from 0.45 to 1.23 by controlling laser beam irradiation time. As applying constant potential while laser irradiation in chloride environments, localized dissolution was occurred only at the laser beam irradiated area, because of the anodic oxide film act as insulator. The corrosion current increases with increasing aspect ratio at the same applied potential, however, aspect ratio of the pit does not show an influence on repassivation behavior of 1070 aluminum alloy.

Formation of Al-Si Composite Oxide Films on Aluminum by Electrophoretic Sol-Gel Coating / Anodizing

Abstract Highly pure aluminum specimens (99.99 %) with electropolishing or DC-etching were covered with SiO2 films by electrophoretic sol-gel coating, and were anodized in a neutral borate solution. Structure and dielectric properties of the anodic oxide films were examined by SEM, TEM, EDX, and electrochemical impedance spectroscopy. It was found that anodizing of both specimens after electrophoretic deposition lead to the formation of anodic oxide films consisting of an inner alumina layer and an outer Al-Si composite oxide layer. The anodic oxide films formed thus had slightly higher capacitances than anodic oxide films on aluminum without any coating. Higher heating temperatures after electrophoretic deposition caused the capacitance of anodic oxide films to increase.