Bending of AZ61 Magnesium Alloy Pipe Subjected to Lateral Load

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This paper deals with possibility of cold and warm bending for cylindrical pipe of AZ61(Mg-6%Al-1%Zn) magnesium alloy. Work piece is a pipe of 22mm outer diameter D and 18mm inner diameter. The pipe of 330mm long with a support distance of 240mm for bending test was prepared. Three kinds of upper bending dies with average bend line radius R of 66, 55 and 44mm were used. Bending tests were performed at four kinds of test temperature (T=293, 393, 473 and 573K) and at a crosshead speed v of 100mm/min. On the bending test, loading was stopped when the bending angle became nearly an aimed angle of 90° or when some cracks occurred on the surface of pipe and the load was rapidly down. Tensile and compressive tests for test pieces cut and finished from the AZ61 alloy pipe were also performed at four kinds of test temperature. The discrepancy between tensile and compressive yield stresses is larger at 293K, but it becomes smaller with increasing the temperature and it nearly equals at 473K and 573K. At every test temperature, in case of R/D=3, the pipe was successfully bent up to the aimed angle of 90° without any damage. However, in case of R/D=2, the pipe had a crack on the inner compressive stress side at 293K and 393K, but it did not have any crack at 473K or over. It suggests that the experimental compressive fracture strain εfc is strongly related to the limit of bendability of AZ61 alloy pipe.