No abstract

AA 1050 aluminum lithographic plates were ac electrograined in nitric acid electrolyte using a flow cell. Scanning electron microscopy was employed to characterize the surface morphology of the electrograined aluminum plate. An epoxy replica technique was utilized to reveal the internal structures of the etch pits. Cross‐sectional transmission electron microscopy was employed for revealing the detailed morphology of the etch pits and the microstructure of the etch film. Together with the surface property measurements such as Ra , Rmax , peak count, and relative increase factor, a pit nucleation and growth sequence is discussed. Numerous hemispherical pits nucleated and grew on the original aluminum surface upon ac electrograining. One‐dimensional and two‐dimensional coalescence of the individual hemispherical pits led to the formation of crescent‐shaped and convoluted pits, respectively. Secondary stage of pit nucleation and growth occurred dominantly on the walls of the convoluted pits. Formation of convoluted pits on the walls of the existing convoluted pits resulted in a pronounced increase in Ra and Rmax . Meanwhile, a decrease in peak count and relative increase factor was observed for prolonged electrograining. In addition, the microstructure of the etch film was closely related to the morphology of the etch pits. © 2000 The Electrochemical Society. All rights reserved.

ZnNi alloy electrodeposited sheet steels were made from a chloride bath using a high-speed flow cell. A Ni-rich flash coating was deposited first, upon which the ZnNi coating, with Ni contents ranging from 8 to 16 wt pct, was subsequently electrodeposited. It is demonstrated that the Ni content of the coating affects the forming properties and microstructure of the ZnNi coatings. The hardness of the ZnNi coating increased with Ni content, leading to poor formability and inferior adhesion of the coated steels, as evident from the large amount of coating loss during swift cupping and coating peel-off during low-temperature adhesion tests. On the other hand, the friction force between the coated steel and cupping die decreased with increasing Ni content. At low Ni contents of 8 wt pct, the coating had a porous equiaxed grain structure. As the Ni content increased, the coating surface changed to dense faceted morphologies. A pyramid morphology was observed for 16 wt pct ZnNi coatings. An X-ray diffraction (XRD) analysis showed that all coatings containing up to 16 wt pct Ni contained only ␥ phase. Transmission electron microscopy (TEM) observations showed the 8 wt pct Ni coating to have a fine-grained structure, which changed to a columnar structure at 16 wt pct Ni. The formation of the columnar structure is explained by the smaller amount of hydrogen discharge as the bath Ni ion concentration increased.