Papers by Keyword: ZK60 Magnesium Alloy

Abstract: Friction stir processing (FSP) is a novel severe plastic deformation technique developed in recent years to produce fine-grained structural materials. In this paper, the microstructure and mechanical properties of ZK60 magnesium alloy prepared by the single-pass and two-pass FSP were studied. The first-pass was subjected with 800r/min-100mm/min and the second-pass was subjected with 600r/min-100mm/min. The results show that the coarse second phase was dissolved into magnesium matrix and the α-Mg grains were remarkably refined in stir zone after FSP. The average grain sizes of the single-pass and two-pass FSP alloys were 6.8μm and 6.0μm respectively. The microhardnesses of the specimens were 70HV and 65HV, the ultimate tensile strengths were 276MPa and 272MPa, and the elongations were 31.6% and 42.5%, respectively. Through increasing the processing pass, the microstructure became finer and the second phase is dissolved more thoroughly. The combined effect of grain refinement and second phase dissolved was responsible for the change of mechanical properties.

Abstract: The microstructural evolution of of as-cast ZK60 magnesium alloy processed by cyclic extrusion and compression (CEC) were studied, and the effects of technical parameters on microstructural evolution were investigated. The results show that the grains of as-cast ZK60 magnesium alloy were obviously refined and uniformed by CEC, the average grain size was decreased from original 50 ~ 60 μm to about 2 μm when the extrusion ratio was 8 with 8-passes at 350°C, and the refinement effect was increased with the rising of extrusion ratio and passes. The effect of increasing passes on grain refinement was not obvious when it exceeds 8. Nevertheless, it is beneficial for the grain homogenization.

Abstract: The high temperature compressive tests of squeeze casting ZK60 magnesium alloy in the testing temperature range of 523-723K and strain rate range of 0.001-10s^-1 were performed on Gleeble-1500D thermal simulator testing machine. Optical microscopy was performed to elaborate on the dynamic recrystallization (DRX) grain growth. TEM observation indicated that the mechanical twinning, dislocation slip, and dynamic recrystallization are the materials typical deformation features. Variations of flow behavior with deformation temperature as well as strain rate were analyzed. Analysis of the flowing deformation behavior and microstructure observations indicated that the flow localization was observed at lower testing temperature and higher strain rates. Dynamic recrystallization occurred at higher testing temperature and moderate strain rates, which improved the ductility of the material. The results indicated that at the testing temperatures lower than 573K and strain rates higher than 1s^-1, the material exhibited flow instability manifesting as bands of flow localizations. These temperatures and strain rates should be avoided in processing the material. Dynamic recrystallization occurs in the temperature range 573-723K and the strain rate range 0.001-0.1s^-1. The number of dynamic recrystallization grains is less at lower temperature and higher strain rate than higher temperature and lower strain rate. The dynamic recrystallization is inadequate at 573-623K while the dynamic recrystallization grain growth has been observed in the temperature range of 673-723K. Therefore it may be considered that the optimum processing parameters for hot working of squeeze casting ZK60 magnesium alloy are 648K and 0.001-0.01s^-1, at which fine dynamic recrystallization microstructure can be obtained.

Abstract: The microstructure and macrotexture of ZK60 alloy sheet were investigated through OM and XRD, which were produced by twin roll casting and sequential warm rolling. Microstructure of twin roll cast ZK60 alloy changed from dendrite structure to fibrous structure with elongated grains and high density shear bands along the rolling direction after warm rolling process at different rolling parameters. The density of shear bands increased with the decreasing of the rolling temperature, or the increasing of per pass rolling reduction. Dynamic recrystallization could be found during the warm rolling process at and above 350oC, and many fine grains could be found in the shear band area. The warm rolled ZK60 alloy sheet exhibited strong (0001) basal pole texture. The formation of the shear bands tends to cause the basal pole tilt slightly to the transverse direction after warm rolling. The intensity of (0001) pole figure increased with the decreasing of rolling temperature, or the increasing of per pass rolling reduction.

Abstract: The effect of different hydrostatic extrusion ratios on the microstructure and mechanical properties of the ZK60 magnesium alloys were investigated. The results showed that, the major deformation mechanism of the alloy is twinning at room temperature, which resulted in that the tensile strengthen and hardness of the extruded alloy improved greatly. With deformation ratio increasing, the ultimate tensile strengthen and hardness are linearly increased, with the functions of Y= 4.2X+358.3 and Y=2.3X +73.69, respectively. And the maximum tensile strength and hardness of the extruded alloy are 383 MPa and 87HB, respectively. But the elongation decreases obviously, the minimum decreasing degree is 50%. With the deformation ratio increasing, the tendency of elongation rate increased as an “M” model.

Abstract: In this paper, the effects of hot extrusion and T5、T6 heat treatment on the microstructures and mechanical properties of ZK60 magnesium alloys are investigated by optical microscope, electronic scanning microscope and mechanical testers. The result shows that both the tensile strength and the elongation of the ZK60 alloy extruded at 380°Care much higher than that of the as-cast alloys, as there are much granular second phases precipitated during the extrusion. The tensile strength of the extruded and T5 treated alloy increases while the elongation decreases faster than that of the extruded alloy. The strengthening effect of the T6 treatment is inferior to that of the T5 treatment. The tensile fracture of the as-cast alloy is brittle fractured while that of the extruded and T5 treated alloy is ductile fractured with lots of deep and even dimples.

Abstract: Effects of hot extrusion processes on grain size of ZK60 alloy tubes was researched by combining numerical simulation with experimental research. The results show that grain size varies inversely as extrusion ratio and extrusion speed, with extrusion temperature being constant. In order to get the finer and homogeneous microstructure, higher extrusion ratio, higher extrusion speed and lower billet temperature should be chosen in the equipment's rated load. Isothermal extrusion is conducive to tube forming , and the smallest grain size and the better microstructure can be obtained at temperature of 300°C when other deformation conditions are constant.

Abstract: Using tensile test of ZK60 magnesium alloy, the superplastic flow behavior was studied. The deformation temperature was set as 280°C, 310°C,340°C, 370°C and 400°C while strain rate was 1×10^-1s^-1, 1×10^-2s^-1, 1×10^-3s^-1 and 1×10^-4s^-1. The results showed that the perfect superplastic behavior was presented at 370°C and =1×10-4s-1 and the maximum elongation could be 133.7%. The biggest factor of strain rate sensitivity was 0.62. The microstructure of the fracture was analyzed used SEM and the results showed that the main deformation mechanism of ZK60 magnesium alloy was grain boundary sliding.

Abstract: The forming limit diagram of magnesium alloy ZK60 was developed with Hill’s instability criterion and M-K analysis. The relationship of forming limit with stain path, temperature and the thickness irregular coefficient were analyzed. The results show that the forming limit of ZK60 magnesium alloy increased little with the rising of strain ratio, but influenced greatly by the failure definition , and forming limit of is increased with the rising of temperature and thickness irregular coefficient, the most suitable value of f0 is 0.99, the fracture occur on the grain boundaries with significant cavities formation.

Abstract: In the present paper a research has been made on the effect of aging on the microstructure and mechanical properties of AZ80 and ZK60 wrought magnesium alloys by virtue of optical microscope, electronic scanning microscope and mechanical testers. The research indicates that both the tensile strength and elongation of AZ80 alloy first increase and then decrease as the aging temperature rises, and that, at 140°C-170°C aging temperature, the alloy has good performances in both tensile strength and elongation, they both reaching their peak values at 170°C aging temperature. It has been proved in these researches that while the hardness of ZK60 alloy first increase and then decrease as the aging temperature rises and that the hardness reaches its peak value at 170°C aging temperature, the impact of toughness of the alloy is just the opposite. ZK60 alloy has good performances in both impact toughness and other properties at 140-200°C aging temperature. Constrastive researches have shown that, at the same aging temperature, ZK60 alloy has a better performance than AZ80 alloy.