Improving the mechanical properties of AZ31 Mg alloy by high ratio extrusion

Experiments were conducted both to evaluate the potential for grain refinement, the subsequent mechanical properties at room temperature in samples of AZ31 Mg alloy and also to investigate the relationship between one-step and two-step high ratio extrusion (HRE). The one-step HRE was undertaken using a high extrusion ratio of 70:1 at 250, 300 and 350 degrees C. And the two-step HRE was conducted with an extrusion ratio of 7 for the first step at 250, 300 and 350 degrees C, followed by a second-step extrusion with an extrusion ratio of 10 at 250, 300 and 350 degrees C. The initial grain size in the AZ31 ingot was 100 mu m and that after one-step HRE became similar to 5 mu m, after two-step HRE at 250, 300 and 350 degrees C were 2, 4, 7 mu m, respectively, resulting in superior mechanical properties at ambient temperature. The microstructure of two-step HRE was finer and uniformer than that of one-step HRE and the strength of one-step and two-step HRE were similar, moreover, the elongation of one-step HRE was improved markedly than that of two-step HRE. Dynamic recrystallization and adjacent grain broking during HRE is introduced to explain the effects of one-step and two-step HRE on the microstructure and mechanical properties of AZ31 Mg alloy. The current results imply that the simple HRE method might be a feasible processing method for industry applications, and the multiply steps extrusion are effective to fabricate high strength of fine grained hcp metals.