In order to investigate the effects of strain rate and temperature on the microstructure and texture evolution during warm deformation of wrought Mg alloy,AZ31 extruded rods were cut into cylinder samples with the dimension of d8 mm×12 mm.The samples were compressed using a Gleeble 1500D thermo-mechanical simulation machine at various strain rates(0.001,0.01,0.1,1 and 5 s- 1)and various temperatures(300,350,400 and 450℃).The microstructure and texture of the compressed samples at the same strain under different deformation conditions were studied and compared by electron backscatter diffraction(EBSD)in scanning electron microscope(SEM).The results show that the size of recrystallized grains in the deformed samples generally increases with the decrease of strain rate and the increase of temperature.After 50%reduction,most basal planes are aligned perpendicular to the compression direction at relatively high strain rate(>0.01 s- 1)or low temperature(<350℃).The optimized strain rate is 0.1 s- 1for uniaxial compression at 300℃,which produces about 80%of small grains(<5μm).
Microstructural evolution of the zirconium alloy deformed at a strain rate of about 1000 s-1 was investigated. Four different strain levels of the zirconium alloy subjected to dynamic compression were designed by several-times impacting at almost the same strain rate. The results show that abundant low angle boundaries at different strain levels were observed in the deformed microstructures, and the quantity and density of low angle boundary increase dramatically with the strain increasing. Besides low angle boundaries and high angle boundaries observed in grain boundary maps, the twin boundaries including the tensile twins {10 2}, {11 1} and compressive twins {11 2} were distinguished at different strain levels, and most twin boundaries were indexed as {10 2} twins. With the stain increasing, the twin boundary density in the deformed microstructures increases indistinctively. Based on the characterization of the deformed microstructures at the different strain levels, the deformation and evolution processes of the zirconium alloy subjected to dynamic loading were proposed. Microhardness measurements show that the microhardness in the impacted specimens increases gradually with the strain increasing, which should be associated with the strain hardening caused by the tangled dislocation.
The three-layer clad materials consisting of Al(AA1100) / Mg(AZ31) / Al(AA1100) plate was fabricated by the hot roll bonding method. The crucial technological parameters of manufacturing clad sheet, including the threshold rolling reduction and clad-rolling bonding conditions were investigated. This clad sheet was produced successfully by hot roll bonding with the intermetallic phase formation, which can be observed using conventional optical microscope. The bond interfacial structures of the AZ31 / AA1100 clad material were observed by SEM. It was be researched that the effect of anneal technology on the thickness of diffusion layer and bonding properties of clad plate. The optimal anneal time is presented based on the micro-analysis for the Mg-Al clad plate. The vital procedures of ensuring the qualities and improving the bonding strength of clad plates were described.
Chen Zejun, Zeng Zhen, Huang Guangjie, Liu Qing Chongqing University, Chongqing 400044, China
Experiments were conducted to evaluate the effects of extrusion ratio on the microstructure and texture developments of AZ31 Mg alloy during forward extrusion. The forward extrusion was undertaken at 400℃ with extrusion ratios of 10, 18, and 25 after the alloy was homogenized at 410℃ for 12 h. Partially recrystallized microstructures were observed in all the extruded rods examined. The texture of the large elongated deformed grains appeared strongly centered at （1010） dominating the extrusion texture, while the recrystallized grains exhibited much more randomized texture. For the alloy with the largest ER （25）, coarse secondary recrystallized grains were found which presented a different texture component with （11 2 0） parallel to the ED. The occurrence of the coarse secondary recrystallized grains in the alloy with the largest ER might be attributed to that the large ER raised the die exit temperature during extrusion and thus promoted significantly grain growth after the extruded rod exited from extrusion die. The intensities of different texture components varied with ER because ER affected the contents of the deformed grains, DRX grains and coarse secondary recrystallized grains. In particular, the maximum intensity of fiber texture was decreased as ER increased due to the decrease of the large elongated deformed grains.
