COMPUTER-SIMULATION OF METAL FLOW IN THE HOT UPSETTING OF A HIGH-STRENGTH ALUMINUM-ALLOY

The effects of metal-working temperature on the hot axisymmetric upsetting of AA 7012 aluminium alloy were investigated in the temperature range of from 250 to 400-degrees-C, at a strain rate of 4 s-1. The material behaviour was studied by means of simulative methods based on the analysis of torsion-test results which have shown that when the strain increases, the flow stress increases to a peak value and then decreases to a fracture value. Furthermore, the flow stress decreases with decreasing strain rate and with increasing temperature. Constitutive equations, describing accurately the hot deformation behaviour of the material, were defined and used subsequently in a numerical model that allowed the coupled thermal-mechanical analysis of hot upsetting. The predictions of forging load versus ram travel and the overall shape changes of the workpiece were compared with experimental results: they were found to be in good agreement with measurements taken in laboratory experiments conducted under similar conditions.