Cavitation of superplastic AA5083 during rapid gas forming

In recent years there have been some efforts to shorten the cycle time for gas forming of superplastic aluminum alloys 5083 with encouraging results. Although it has been worked on by one or two predecessors, we are the first to do extensive research in this area and we successfully demonstrated that only ∼70 seconds (shortest time yet) was needed for creating a circular cup (40mm in diameter and 20mm deep) out of 2mm thickness flat sheet at 500°C. However, before the rapid gas forming process can be accepted and adopted by the industry, cavitation condition needs to be shown that it will not deteriorate with respect to products obtained by conventional processes of much lower speeds. With this objective in mind, numerous circular-cup forming procedures were performed at various conditions to yield raw data for analyzing the effect of strain, strain rate, back pressure and temperature on cavitation. The results and discussion of this paper indicate that in fact, strain is the most influential factor in cavity formation while the effect due to strain rate is subtle or even negligible. Experiments at various temperatures suggest that cavitation increases as it decreases. However it is also informatively pointed out that this may merely be an indirect effect of temperature because material's flow stress increases when it is lowered, and thus more cavitation may actually be due to the resulting higher stress.