Superplastic forming of shells from sheet blanks with thermally unstable coatings

Abstract

The article is devoted to superplastic forming of non-uniformly heated sheet blanks from aluminum alloy AMg6M. To create an uneven temperature field over the surface of the blank, coatings made of sublimated substances were used from at temperatures 50…150°C below the superplastic forming temperature (450°C for AMg6M alloy). An aqueous solute of chloride and ammonium iodide having a sublimation temperature at normal pressure and a latent heat of conversion equal to 338 and 404°C, 330 and 355kJ/kg, respectively, was sprayed onto the central zones of the blanks. Superplastic forming of shells was carried out in two modes: 1) with simultaneous sublimation of the coating; 2) with the beginning of the sublimation of the coating upon reaching the height, which is formed by the workpiece, equal to 20-30% of the final shell height. The experiments showed a decrease in the thickness of the shells to be formed up to 4-10% on the working surface of the shells (without taking into account their flange zones) and the savings of sublimate during superplastic forming in the second mode. The optimal subliming coating for AMg6M alloy was ammonium chloride.