Effects Of Microstructure On Plastic Formability In ZK60 Magnesium Alloy Sheets

With the occurrence of the idea of lightweight and the promotion of low-carbon transportation,magnesium and its alloys have embraced more and more widespread application in domestic vehicles,aviation,aerospace etc.due to their pros such as low specific weight and high specific strength.However,one of the most striking cons is that the limited ambient formability caused by the hexagonal close packed crystal lattice results in sparse industrial application.Based on the regrettable status quo,utilizing ZK60 magnesium alloy as research material,the influence of microstructure on formability was revealed to highlight the most suitable microstructure conducive to the enhancement of formability,which laid a certain theoretical foundation and data support for the improvement of magnesium sheets formability.ZK60 thin sheets under three different techniques,namely,hot rolling,cross rolling and asymmetrical rolling,were successfully fabricated.It was revealed that with the rolling pass adding,the basal texture of ZK60 thin sheet exhibited a gradual centration from around to the normal direction and the grain size was reduced from 59.8 of the extruded to 4.64.The texture of asymmetrical rolling resembled hot-rolled sheet and obtained ZK60 thin sheet with grain size of 5.8.A strong base texture of ZK60 thin sheet with grain size of 6.0 was obtained by cross rolling.Whereafter,we further analyzed the mechanical properties of the ZK60 thin sheets and the results were as following.In fine-grained sheets weaker the texture,lower the yield strength and higher the uniform elongation.The fine-grained sheets with weak texture acquired by asymmetrical rolling achieved in relatively low yield strength of 145.1MPa and comparatively high uniform elongation of 20.9%.By contrast,the fine-grained crossrolled sheets exhibited 229.9MPa in yield strength yet only 12.9% in uniform elongation in transvers tensile loading.Three point bending test and bulging test were carried out aiming at the characterization of formability to reveal the effect of texture on the formability.The results indicated that weak basal texture sheet possessed smaller bending radius and in sheet with strong basal texture ample {10-12} tensile twinning came into existence and crack most likely appealed on the interior side.Further bulging test suggested better formability due to the easier joint activation of slip and twinning in the primitive compressed sheet resulted in the fact that the first principle strain reached 19.4% and the first principle strain arrived at 13.7% which was quite insufficient because of the reduction in twinning irrespective of abundant slip.The worst formability came to strong {0002} basal texture with mere 11.8% in that momentarily basal texture is not conducive to neither the slip activation nor the twinning formation.Aiming at further promotion of the formability of ZK60 thin sheet,high temperature tensile test were carried out at 373 K to 573 K.At the temperature of 373 K,the elongation of the sheet reached 107%,which was enhanced to nearly 5 times of ambient elongation(23%).At the temperature of 473 K,the elongation continued to climb up to 137% in both RD(rolling direction)and TD(transvers direction),which revealed a moderate improvement in contributed to plasticity enhancement and the influence of texture on orientation gradually weakened when the temperature is below 200℃.At 573 K,strained along rolling temperature the elongation had already reached 862%.It exhibited more adorable high temperature plasticity,which was correlation with grain boundary activation.The texture analysis of samples elongated at different temperatures demonstrated that there appeared strong typical basal texture and it played a leading role in plastic deformation at 327 K.However,with the increment of temperature to 473 K and 573 K,weak basal texture formed and non-basal slip had been massively initiated.