Study of the cyclic extrusion–compression in production of high stringed and ultrafine grained AM60 Magnesium noncircular thin section beams

In this study a new severe plastic deformation method named noncircular thin section cyclic extrusion–compression (NCTS-CEC) is proposed for processing ultrafine-grained noncircular thin section beams. In this technique, the total length of noncircular L shaped section is passed through a neck zone and experiences severe plastic strains. Therefore, the high amount of accumulated plastic strain could be imposed by repeating the number of process cycles. In the first section of study, the AM60 Magnesium alloy is inserted into die and deformed by punch in different cycles. The observations by optical and SEM microscopes showed the formation of about 5 μm fine grains from the initial value of 75 μm after processing by two cycles of the NCTS-CEC. Also, the mechanical properties including yield strength, UTS, elongation and microhardness are evaluated at different cycles of NCTS-CEC processing. The obtained results showed the increase of yield strength and UTS to 136.9MPa and 286.7 MPa from the initial values of 89.5 MPa and 227.3 MPa, respectively. The Vickers microhardness is increased to 89HV from the initial value of 54HV at the end of second cycle. Also, the elongation of processed sample is increased to 14.4% from 11.3% due to texture evolution, grain refinement and breakage of brittle eutectic phases at the end of second cycle. The cellular automaton (CA) finite element method was implemented to simulate the process to predict the microstructure evolution of AM60. The obtained results from cellular automaton finite element (CAFE) and experimental methods were in good agreement.