Hot formability characterization and fracture locus determination of the CuZn40Pb2 brass alloy through tensile and torsion testing

The prediction of ductile fracture occurrence in hot forging processes is one of the main industrial issues, which needs damage models that have to be on one hand accurate and easily calibrated, but also easy enough to be industrially implemented an utilized. Tensile testing formability characterization, although experimentally easy, does not allow taking into account all the variables influencing the evolution of damage, making the calibration test-dependent. Besides the stress triaxiality factor effect, in hot forging processes, the stress deviatoric parameter, the temperature and strain rate must be taken into account to provide reliable and efficient models. In this work hot fracture characterization was performed on the dual-phase brass alloy CuZn40Pb2, typically used for hot forging and characterized by a narrow temperature window of formability. The values of true strain at fracture from tensile, torsion and tensile-torsion tests performed at various temperatures and strain rates are obtained. Numerical simulations of the above-cited tests were carried out in order to determine the three-dimensional surfaces of the fracture locus as a function of the stress triaxiality and deviatoric parameter. The results are critically discussed and in particular the influence of the rheological behaviour of the material on the fracture locus shape is highlighted. Optical microscopy analysis was carried out in order to assess the testing parameters influence on the phase distribution and EDS-SEM analysis to evaluate the grain boundary composition, which was recognized critical as regards the formability characteristics of the investigated alloy.