Abstract: A process for exposing silicon crystals on the surface of an aluminum alloy of high silicon content and with undissolved silicon particles, wherein the aluminum alloy is connected as the cathode in an electrolyte containing an aqueous alkali nitrate solution which is at least 0.01 molar with respect to the nitrate ions and is subjected to electrolysis with a minimum current density of 0.5 A/dm.sup.2 to remove aluminum from the alloy surface without removing silicon crystals. The electrolyte can also contain at least 0.005 mol/l fluoride ions and 0.05 mol/l-14 mol/l nitrite ions to suppress generation of hydrogen at the cathode and oxygen at the anode, respectively.