| As the most representative Zn alloy system,superplastic Zn-Al alloy can be used as a potential seismic material with the characteristics of low flow stress,no work hardening,and high elongation.And the alloy still maintains good plasticity at room temperature and high strain rate(10?500/s),and the elongation reaches 30%.However,due to the "aging"phenomenon of the biphasic organization,its further development is limited.Recently,fine-grained superplastic Zn-Mn and Zn-Ni-Mg alloys have shown good high-temperature superplasticity.The addition of Mg element can achieve significant strengthening of Zn alloy,and the addition of Mn can greatly improve the plasticity of Zn alloy.However,the above mentioned alloys are often refined by using the severe plastic deformation(SPD)process.Earlier work found that the conventional rolling process can refine the Zn-Mg-Mn alloy structure to the same level(sub-micron scale)as the SPD process.It is expected to show good plasticity at different strain rates at room temperature and be used in superplastic fields and seismic materials.At present,there are no studies on the mechanical properties and microstructure(grain boundary type,dislocation slip system,texture,etc.)of rolled Zn-Mg-Mn alloy after tensile tests at different room temperature strain rates.Therefore,based on earlier work,this paper uses rolling technology as a means of preparation.Scanning electron microscope(SEM),X-ray diffraction(XRD),electron backscatter diffraction(EBSD),transmission electron microscope(TEM),room temperature dynamics(high speed:1×10-1/s or more)and low and quasi-static(1×10-1/s?1×10-4/s)strain rate tensile,to study the mechanical properties of rolled Zn-0.1/0.2Mg-1 Mn alloy and the microstructure after tensile fracture.And analyze the mechanical properties and deformation mechanism after tensile fracture at different rates.In order to better understand the relationship between strain rate with microstructure and mechanical properties.At the same time,the corrosion resistance of the alloy was studied.The main conclusions reached are as follows:300? conventional rolling achieves the preparation of ultrafine crystals,and the average grain size of the rolled Zn-0.2Mg-1Mn alloy is 0.39 ?m.The stress state sensitivity index m at the strain rate of 1×10-4/s is 0.20,and an elongation of 248%is obtained,which shows good room temperature superplasticity.The average grain size of rolled Zn-0.1Mg-1Mn alloy is 0.49 ?m,and the m value is 0.25.The above two alloys have the same superplastic characteristics.In the rolled Zn-0.1/0.2Mg-1Mn alloy,the grains will grow after tensile fracture at a rate of 1×10-4/s,reaching 0.54 ?m and 0.51?m.However,it is still ultrafine crystals,showing good structural stability.The texture orientation is changed from the initial rolled plate texture:the {0001} base surface of the grains is ±15?25° from the rolled surface,to the {0001} base surface deviates from irregular angles with the the rolled surface as a weak texture.It is shown that grain boundary sliding and grain rotation play a dominant role in the process of room temperature superplastic deformation.When the rolled Zn-0.1/0.2Mg-1Mn alloy is stretched at a high rate of 1/s-100/s,the elongation and strength no longer change significantly,and the elongation does not exceed 0.5%.As the rolling state of Zn-0.1Mg-1Mn and Zn-0.2Mg-1Mn alloys at the dynamic rate activates more non-basic plane<c+a>dislocation slip type,the slip system is {1122}<1123>.This kind of dislocations are difficult to continue to slip and cause stress concentration after excitation,making the lower strain rate sensitiveConsistent with the low rate 1×10-4/s stretching,the texture of the rolled Zn0.1/0.2Mg-1Mn alloy also undergoes orientation changes after high speed tensile fracture,and the Zn-0.1Mg-1Mn alloy is more significant.Orientation of rolled plate texture:{0001} base surface and rolling surface are ±15°?25°,while<0001>crystal direction and RD direction are±65°?75°,making the non-base surface slippery Schmidt factor higher and easy to start.After the dislocation started,the texture changed to {0001}basal plane with rolling plane,and the<0001>crystal direction with rolling direction deviated from random angles.The corrosion test shows that the rolled Zn-0.1/0.2Mg-Mn alloy has strong corrosion resistance.The increase in weight loss gradually slowed down with time,and the steady-state weightlessness rate finally maintained at 0.1 mg/cm2·h and 0.08 mg/cm2·h It is shown that the formation of ZnO and Zn5(OH)8Cl2 provides protection for the matrix,thereby improving the corrosion resistance of the rolled Zn-0.1/0.2MgMn alloy. |
PDF Full Text Request