Grain Refinement after Various Thermo-Mechanical Treatments in AZ80 and ZK60 Magnesium Alloys

The effect of thermal processing prior to severe plastic deformation by extrusion and swaging on grain refinement in ZK60 and AZ80 alloys was studied. The alloys received in direct-chill cast condition were homogenized at 415C and annealed (over-aged) at temperatures from 200 to 380°C. Both the direct-hill cast and over-aged conditions were extruded at T = 300C using an extrusion ratio of ER = 19. Hot extrusion resulted in substantial grain refinement in both cases, the effect being stronger in the over-aged material. The extruded bars were severe plastically deformed at 250C by swaging. Swaging refined further the grain size depending on the deformation ratio (number of passes). At optimal processing conditions the grain size was 450 nm and 570 nm for the AZ80 and ZK60 alloys, respectively.