Uniaxial Deformation, Charpy and Fracture Toughness Testing of Extruded Magnesium Alloy AM30 2010-01-0406

Effects of strain rate and temperature on tensile, compressive and toughness properties were investigated for an extruded Mg alloy AM30 in both extrusion (ED) and transverse (TD) directions. The effects of strain rate and temperature on uniaxial flow stress were reported elsewhere but will be briefly described to facilitate the understanding of Charpy results (i.e., load, deflection and absorbed energy). The effects of loading rate from quasi-static to 5.1 m/s on un-notched and V-notched Charpy load-deflection curves up to maximum load were negligible, but load up to maximum load increased with decreasing temperature. The deflection at rapid load-drop in un-notched Charpy tests increased with decreasing loading rate and increasing temperature between -50°C and 100°C for un-notched ED and TD specimens (i.e., L-T and T-L specimens according to ASTM E 1823 terminology). The effects of loading rate and temperature on load up to maximum load of un-notched Charpy specimens could be explained using their effects on flow stress and the tensile-compressive yield asymmetry combined with a mechanics analysis of a bend bar; that is, the neutral axis is not in the specimen center because of the yield asymmetry. The absorbed energies of un-notched Charpy specimens increased with decreasing loading rate and increasing temperature; absorbed energies of V-notched Charpy specimens were very low and did not show effects of loading rate and temperature. Fracture toughness (J_I

) was measured and showed higher values in the L-T compared with the T-L orientation, probably owing to the texture and associated activation of twinning in T-L specimens.