Effects Of Isothermal Plastic Deformation On The Microstructure And Mechanical Properties Of Mg-Al-Zn Magnesium Alloys

Studies on magnesium alloy thermal formability focus on Mg-Al-Zn and Mg-Zn-Zr alloys. However, the researches for high-strength magnesium alloys based on common alloys are still limited.AZ63M magnesium alloy in this paper is a newly developed Mg alloy fabricated by the addition of Y, Li, Zr et al. in AZ63 alloy. The mechanical properties and microstructure evolution on different deformation conditions were investigated by extrusion experiments, tensile and compression tests at elevated temperature, forging experiments. The main results are as follows:With the increasing of extrusion ratio from 9～81, the average grain size decreases from 24μm to 8μm, the UTS increases from 277MPa to 376MPa, the A5 decreaes from 16.1% to 15.3%. In the extrusion temperature of 350℃, with the extrusion holder temperature decreasing from 300℃ to 200℃, the alloy grain size decreases from 31μm to 14μm, the UTS increases from 255MPa to 368MPa, the A5 increases from 13.6 to 17.3%. When holder temperature is 250℃ and extrusion ratio is 32, the UTS of extruded-T6 (420℃×8h,210℃×18h) alloy increases from extruded alloy 330MPa to 390MPa, the A5 compared to extruded alloy decreases by 6%.In the deformation temperature range of 300℃～450℃, initial strain rate of 5～10-4s-1～5×10-2s-1 (high temperature compression) and 10-4s-1～10-2s-1(high temperature tension), the constitutive equations are established, namely: ε=1.23×108[sinh(0.0224a)]2.63exp(-1.30×105/RT); ε=6.62×104[sinh(0.0158a)]1.51exp(-98000/RT).By extrusion process the hot workability improves for AZ63M magnesium alloy.The optimal compression temperature is determined to be 400℃～425℃. During Multi-directional forging, along with the cumulative strain increseas, the compression yield strength of the alloys increase and the central part is superior to the marginal part.