Quick plastic forming of aluminum alloy sheet metal

A method of forming an article of manufacture from superplastic magnesium-containing aluminum alloy sheet stock, comprising

• providing a sheet forming tool having a peripheral surface against which the periphery of said sheet stock can be held in sealing engagement and a sheet forming surface within said peripheral surface for forming said sheet, said tool including means for venting said cavity during the forming of said sheet,
• heating said sheet to a temperature in said range and holding said sheet in sealing engagement with said peripheral surface of said tool, said sheet then having a first surface facing said forming surface and an opposite surface,
• stretching said heated sheet into conformance with said forming surface by applying working gas pressure to said opposite side of the sheet, said stretching being accomplished by continually increasing said pressure from ambient pressure to a final stretching pressure in the range of about 250 psi to about 500 psi above ambient pressure and completing said stretching within a period of up to about 12 minutes.

A method of stretch forming a magnesium-containing, aluminum alloy sheet into a product, said alloy comprising up to about 6% by weight magnesium and having a microstructure characterized by a grain size in the range of about 5 to 30 micrometers, said method comprising

• heating said sheet to a temperature in the range of about 400° C. to about 510° C. and
• stretching at least a portion of the heated sheet so that one side of the sheet is brought into conformance with a shaping surface by applying working gas pressure to the opposite side of the sheet, said stretching being accomplished such that at least a portion of the sheet experiences a strain rate greater than 10−3 sec−1.