Furong Cao

Flow instability criteria in processing map of superalloy GH79

Abstract Hot compression tests were conducted on a Gleeble-1500D thermal simulating tester. Based on the deformation behavior and microstructural evolution of superalloy GH79, different types of instability criteria of PRASAD, GEGEL, MALAS, MURTY and SEMIATIN were compared, and the physical significance of parameters was analyzed. Meanwhile, the processing maps with different instability criteria were obtained. It is shown that instability did not occur when average power dissipation rate was larger than 60% in the temperature range of 900–930 °C and 960–1080 °C, corresponding to the strain rate range of 5×10 −4 −1.8×10 −1 s −1 and 5×10 −4 −1.5×10 −1 s −1 , respectively. The two domains are appropriate for the processing deformation of superalloy GH79.

Force analysis and experimental study of pure aluminum and Al–5%Ti–1%B alloy continuous expansion extrusion forming process

Abstract The deformation zone of CONFORM extrusion was divided into primary gripping zone, gripping zone, conical expansion chamber zone, cylindrical zone and sizing zone of die, and corresponding force equilibrium equations were established using the Slab method. The deformation force formulae of CONFORM machine at any wrapping angle with an expansion chamber were obtained. Experiment on pure aluminum and Al–5%Ti–1%B alloy was conducted on the CONFORM machine self-designed. The resistance to deformation of Al–5%Ti–1%B alloy at the deformation temperature of 400 °C and the strain rate of 3.07 s −1 was measured to be 50 MPa using Gleeble–1500 thermal simulation machine. The calculation results of deformation forces for CONFORM process with an expansion chamber for pure aluminum and Al–5%Ti–1%B alloy were given. The experimental CONFORM radial force is in agreement with the radial force obtained by theoretical formula.

Extrusion force analysis of aluminum pipe fabricated by CASTEX using expansion combination die

Abstract To determine the extrusion force of pipe fabricated by continuous casting and extrusion (CASTEX) using an expansion combination die, the metallic expansion combination die was divided into diversion zone, expansion zone, flow dividing zone, welding chamber, and sizing zone, and the corresponding stress formulae in various zones were established using the slab method. The deformation zones of CASTEX groove were divided into liquid and semisolid zone, solid primary gripping zone, and solid gripping zone, and the formulae of pipe extrusion forces were established. Experiments were carried out on the self-designed CASTEX machine to obtain the aluminum pipe and measure its extrusion force using the expansion combination die. The experimental results of radial extrusion force for aluminum pipe are in good agreement with the calculated ones.

Modeling of deformation energy at elevated temperatures and its application in Mg–Li–Al–Y alloy

Abstract To control the superplastic flow and fracture and examine the variation in deformation energy, the stress and grain size of Mg–7.28Li–2.19Al–0.091Y alloy were obtained using tensile testing and microstructure quantification, and new high temperature deformation energy models were established. Results show that the grain interior deformation energy increases with increasing the strain rate and decreases with increasing the temperature. The variation in the grain boundary deformation energy is opposite to that in the grain interior deformation energy. At a given temperature, critical cavity nucleation energy decreases with increasing strain rate and cavity nucleation becomes easy, whereas at a given strain rate, critical cavity nucleation energy increases with increasing temperature and cavity nucleation becomes difficult. The newly established models of the critical cavity nucleation radius and energy provide a way for predicting the initiation of microcrack and improving the service life of the forming parts.