Effects of temperature on yield locus for 5083 aluminum alloy sheet

Warm press forming of aluminum alloy sheets is quite attractive, since undesirable stretcher strain marks, which often appear on the surface of the sheets during cold press forming, will disappear at high temperature, and furthermore, some aluminum alloys exhibit high-temperature superplasticity at a certain forming speed. In order to determine the optimum condition of press forming for an aluminum alloy sheet, the effect of forming temperature on the yield locus was experimentally investigated. The yield locus for a fine-grain Al-Mg alloy (5083-O) sheet was obtained by performing biaxial tensile tests, using cruciform specimens, at temperatures of 30, 100, 170, 250 and 300°C at strain rate of 10s^-1. The size of yield locus drastically decreased with increasing temperature. Neither von Mises' criterion or Hill's can well predict the shape of the yield locus of this sheet metal. Instead of these quadratic yield functions, the yield criterion of Logan-Hosford or Barlat is a better choice for the accurate description of biaxial stress-strain responses at a high temperature.