Effect Of Homogenization On Microstructure And Mechanical Properties Of ME21 Magnesium Alloy And Its Distortion Caused By Machining

The effect of homogenization process on microstructure and mechanical properties, anisotropy, work hardening exponent of ME21 alloy extruded plates were investigated. To compare the differences of residual distortion of magnesium plates, two evaluation measures was established, and the main results shown as follows.The solute atoms in ME21 cast alloy annealed at 420? have sufficient energy for diffusion. The uniformity of the microstructure is sufficient in ME21 alloy which is homogenized by 420?×4h. The mechanical properties at room temperature of as cast alloy which were uniformed by the rang of 420? to 520? can not be improved. The strength and ductility of the alloy decreased after homogenization by 420? and 470?. The tensile strength of the alloy uniformed by 520 ? is about 150 MPa, and the elongation is about 6%, which is close to as-cast alloy. The yield strength of the as cast ME21 was little affected by the homogenization annealing temperature.To obtain the best solution of the alloy, it is necessary to use high temperature homogenization and low temperature extrusion to make the alloy to be cooled quickly. ME21 Ingot(?80 mm) in the heating furnace cooled fast from 520? to 450? is about 7'15”, the temperature difference of different test points can be controlled within 5?, furnace fast cooling method is feasible.The tensile strength and elongation of the extruded sheet which is homogenized by 420?×4h is consistent in different directions without obvious anisotropy, and tensile strength is in the range of 241 MPa to 254 MPa, elongation at 16%~17.5%. The strength anisotropy of the extruded plate which is uniformed by 470×4h? is minimum, the tensile strength of different directions is about 244 MPa, yield strength is about 185 MPa, elongation is about 9.7%, which restricted the elongation anisotropy. The tensile strengthes in different directions of the extruded sheet which is homogenized by 520?×4h are all 10~30MPa lower than 470?×4h, and elongation is not too much high.For ME21 extruded sheets, the strength and yield ratio in transverse direction are likely to be with the increase of homogenization temperature decreased, but it is more advantage of 470? in the extruded direction. The strength and yield strength ratio in central and edge of extruded sheet which is homogenized by 520?×4 is more uniform. The elongations in of extruded plate which is uniformed by 420?×4h in edge and central are more close.The anisotropies of strain hardening exponent and yield strength ratio have a good correspondence. The strain hardening exponents of as-extruded ME21 alloy which are homogenized by different processes are increased with the increase of homogenization temperature. The strain hardening exponent difference of extruded plates which are uniformed by 420? and 470? is smallest. The strain hardening exponent of the extruded sheet which is homogenized by 520? is remark increase. The strain hardening exponent anisotropy of extruded plate uniformed by 470? is smallest.With the increase of homogenized temperature, the degree of recrystallization increased. There are a number of un-completed recrystallization gains as strip distributed along the extrusion direction in the extruded sheet which is short heating by 420?, and it's microstructure is very uneven. The size and area of recrystallization zone of the extruded sheet which is homogenized by 420?×4h was decreased. The recrystallization area increases, the un-crystallization area and the distribution of dispersion in the extruded plate which is homogenized by 470?×4h. The recrystallization is more adequate, nu-recrystallization of the block structure is very small, very uniform macro in the extruded sheet which uniformed by 520?×4h.The compound phase was clearly broken in extrusion process, and it was distributed in interdendritic which is like the distribution of compound phase in as-case alloy. The size of dendrite arm is about 20~50?m, which is very similar to the unit of compound phase. The heritability of compound distribution before and after deformation was reflected.A device and method for testing and evaluating the degree of deformation of the plate machine is developed, which is used to prove the relationship between the yield strength ratio and the sensitivity of deformation after machining. For magnesium alloy extruded plates with different compositions or homogenized by different temperatures, the bigger the yield ratio, the smaller the deformation degree of the plate mill.