Effect of Friction and Back Pressure on the Formability of Superplastically Formed Aluminium Alloy Sheet
This paper examines the effect of friction and back pressure on the formability of superplastically formed aluminium alloy AA7475 sheet at the temperature of 517 °C. Several experiments with lubrication and back pressure are performed using a simple box shape tool cavity. The coefficient of Coulomb friction between the formed sheet and tool has been determined indirectly using a finite element model to simulate superplastic forming of the box shape. Typical values determined for all lubricant conditions tested are in the range 0.1 < μ < 0.2. The void growth with strain was determined directly from measurements as a function of back pressure. The results show the application of back pressure at 1 MPa reduces the growth of voids from 7% to 0.3% void volume fraction at a logarithmic thickness strain of 0.65. This paper reports back pressure has a significantly greater role than friction in enhancing the formability of the alloy.
J.R. Duflou, R. Clarke, M. Merklein, F. Micari, B. Shirvani and K. Kellens
P. Wood et al., "Effect of Friction and Back Pressure on the Formability of Superplastically Formed Aluminium Alloy Sheet", Key Engineering Materials, Vol. 473, pp. 532-539, 2011