The mechanism of electrograining aluminium sheet in nitric/boric acid electrolyte

Electrograining of aluminium in HCl: effect of the alloy for high‐speed processing lines

“…When EG process proceeds with time, the initial benefits from the presence of Zn or Mg as intermetallics or in solid solution are inevitably masked because these particles are removed from the surface and thus they do not play a primary role once pitting is initiated. [13] However, the initial morphology created is the germ that accelerates the process, a situation that can be confirmed considering the following facts: (i) the reduction of the processing time to slightly lower values (30 s, with apparently full EG surface) promotes a quite better performance in samples B and C as no plateaus are found as in the case of sample A; (ii) the etching effect in alloys doped with Zn and Mg is up to 15% higher looking at the weight losses when the smut is removed (60.4, 70.1 and 70.3 mg/dm 2 for A, B and C, respectively); and (iii) by means of interferometry images (Fig. 4), some streakiness is usually found in the purest metal, as the lower the pit size, the more difficult it is to mask other topographical features on the surface (in other words, the stronger pitting activity in metals B and C quickly soften the initial roughness).…”

“…In this case Mg is selected because, contrary to other strengthening elements such as Mn, it provides a better topography of round and low-size pits and avoids the apparition of residual flaws, [12] especially in HCl. [10,13] …”

Importance of Etch Film Formation During AC Controlled Pitting of Aluminium

“…It is known that during electrograining an etch film is formed masking the aluminium surface, mainly composed of hydrated aluminium ( Figure 6) [Thompson & Wood, 1978, Dowell 1986, Terryn, 1987, Marshall, 1995Laevers, 1996, Amor & Ball, 1998]. The film formation mechanism, morphology and weight differ upon different graining conditions therefore a thorough investigation of several parameters is necessary.…”

Effect of magnesium and titanium on the cathodic behaviour of aluminium in nitric acid

“…Nitric acid is one of the electrolytes that can be employed for the electrograining of lithographic plates, manufactured from AA 1050 aluminium alloy, that are used for offset printing . The electrograining procedure involves cycling of the potential of the alloy, such that anodic film formation followed by pitting occurs under anodic potentials and hydrogen evolution, with associated deposition of hydrated alumina, under cathodic potentials . The cathodic polarization has an important role in ensuring uniformity of pitting during the anodic part of the cycle .…”