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.
Highlights
The main disadvantage of the process of shells superplastic forming (SPF) from sheet blanks [1,2,3] is the large variability of the walls along the contour of products
We have proposed a new method for regulating of the metal flow at SPF by applying the thermally unstable coatings onto the sheet blank, which, due to a given thermal effect on the blank, changes its temperature field and formed local thicknesses
In the case of superplastic forming of shells, the variability of walls thickness can be reduced by creating an uneven temperature field along the workpiece surface during forming
Summary
The main disadvantage of the process of shells superplastic forming (SPF) from sheet blanks [1,2,3] is the large variability of the walls along the contour of products. There are a number of ways to regulate the metal flow during plastic forming, in particular, elimination of products thickness variability. They provide the preliminary profiling of the blank or semi-finished product, changing the structure of the metal of the blank and the face friction conditions at the "workpiece-die" border, and SPF in an uneven temperature field. SPF process in this case provides, as a rule, two-stage molding by pneumomechanical (PMF) or reversible forming (RF) methods. The thickness distribution in the product is close to uniform
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