Cylindrical extrusions of magnesium AZ31B were subjected to quasi-static axial cutting and compression modes of deformation to study this alloy’s effectiveness as an energy absorber. For comparison, the tests were repeated using extrusions of AA6061-T6 aluminum of the same geometry. Axial cutting of AA6061-T6 extrusions has been shown to be an effective, ductile mode of energy dissipation, yielding a repeatable, nearly constant load/deflection response with a crush force efficiency (CFE) up to 96%. In the present tests, the quasi-static cutting deformation of AZ31B extrusions achieved a respectable CFE of 80%, but revealed a load/deflection response with sharp, minute, rapid fluctuations, indicating an undesirable fracturing failure. Additionally, the average specific energy absorption (SEA) of AZ31B was 11 kJ/kg, which is less than half that seen for AA6061-T6 extrusions of the same geometry (24 kJ/kg). An analytical model of the cutting deformation of AA6061-T6 extrusions can predict the steady state cutting force to within 10%. However, the model did not agree well with the experimental results of AZ31B, yielding approximately 150% error. This deviation is likely attributed to the brittle deformation nature of AZ31B that is not accounted for in the model. For the axial compression tests, three different end geometries were considered, namely (1) a flat cutoff, (2) a 45 degree chamfer, and (3) a square circumferential notch. AZ31B extrusions with the 45 degree chamfer produced the most repeatable and stable deformation of a progressive fracturing nature, referred to as sharding, with an average SEA of 40 kJ/kg and an average CFE of 45 %, which are nearly equal to the performance of the AA6061-T6. Both the AZ31B specimens with the flat cutoff and the circumferential notch conditions were more prone to tilt mid-test, and lead to an unstable helical fracture, which significantly reduced the SEA.