The effects of 0.4wt% yttrium (Y) addition, annealing, and annealing+aging on the hot compression behavior of cast AZ80 were studied at strain rates between 10(-4) and 10(-2)s(-1) and temperatures ranging between 573 and 673K. The apparent activation energies of the as-cast AZ80 and AZ80 + 0.4Y were 122 and 182kJ/mol, respectively. Shear bands formed in each alloys. Compared with the as-cast AZ80, more shear bands formed, and a larger volume of cracks initiated and propagated from the grain boundaries and shear bands in as-cast AZ80 + 0.4Y. In general, Y addition increased the peak stress at lower temperatures and higher strain rates. The annealed and annealed+aged alloys exhibited more shear bands and larger compressive peak stresses than their respective as-cast counterparts after compression at 573K, 10(-2)s(-1). There were more shear bands in the annealed and annealed+aged AZ80+0.4Y compared with AZ80 after compression at 573K, 10(-2)s(-1). Fine precipitates appeared in the shear bands of AZ80+0.4Y. The average width of the shear bands increased with increasing temperature and decreasing strain rate, and the angles of intersection between the different shear bands were approximately 90 degrees.