| As the lightest structural materials,magnesium alloys(Mg)have received considerable attention owing to their high specific strength,specific stiffness,thermal conductivity,and good electromagnetic shielding performance.However,the poor plastic workability,low yield strength and poor wear resistance,greatly limit the application of Mg alloys.In this paper,the deformation mechanism during hot compression,the effect of aging treatment on microstructure and properties and the evolution of subsurface microstructure during dry sliding friction of Mg-6Al-3Zn-2Sn alloy were studied,which provides an important theoretical and scientific basis for the development and processing of high-performance magnesium alloys.The results of thermal compression at different strain rates at 300°C show that the activated twins were mainly{10(?)2}tension twins at the initial stage of isothermal compression.The twin–twin intersections occurred under different strain rates,and the higher strain rate compression accelerated the twinning behavior.The preferentially nucleated twin variants followed the SF criterion.At a lower strain rate,isolated twin variants with 60°<10(?)0>boundary owing to twin intersection will coordinate plastic deformation through the lattice rotation.The high dislocation density inside the twins at a high strain rate is likely to form new grains from subgrain boundaries(SGBs)through high-density dislocation and 60°<10(?)0>boundaries effect of twin–twin intersection.Compared with low strain rate,there are more softening mechanisms under variable strain rate,such as TDRX,dynamic recrystallization induced by twin–twin intersection and the lattice rotation caused by twin–twin intersection,which significantly increases the volume fraction of dynamically recrystallized grains.It is found that the volume fraction of Mg17Al12 phase increases and the Mg4Zn7phase precipitates after the aging of the as-extruded ATZ632 alloy.Both the yield strength and ultimate tensile strength of the peak-aged ATZ632 alloy reached 252.5 and416.2 MPa,respectively.And after peak aging,multiple lamellar Mg17Al12 phases precipitated and grew parallel to the basal plane of the matrix;furthermore,the rod-like Mg4Zn7 phase grew perpendicular to the basal plane.The precipitation of Mg4Zn7 as the main strengthening phase improves the yield strength of the alloy,and the precipitation of Mg17Al12 phase and the fine grain strengthening further improve the strength of the alloy.Because of the rotation of some part of the non-static recrystallized grains during aging,the pyramidal plane was parallel to the rolling direction,weakening the basal texture and the strength of alloy.The dry sliding fraction tests were performed with loads of 20N,60N,and 120N.The results showed that friction coefficient decreased as the load increased.The wear mechanisms under 20N and 60N loads are mainly abrasive wear and delamination wear,respectively,and under 120N load are oxidation wear and delamination wear.Twins were detected in the subsurface microstructure after dry sliding fraction under different loads,and they were all tensile twins.The number of tensile twins is maximum at 60 N load,and fine recrystallized grains are seen at 120 N load.Schmidt factor(SF)was calculated using the resultant force of load and friction force.The calculation results show that:the fraction of twins with a negative SF value increases as the load rises,and all six types of twinned variations are produced with the(011 2)[01 11]twin variant as main.The generation of twin variants for twins with negative SF values follows the geometric coordination factor,and the growth direction is affected by the value of8)8)~′.The larger the grain size,the more easily twins are generated during dry sliding fraction.Grains having a high SF value of basal slip,which is greater than SF value of twins,are prone to twinning.Under a low stress,twinning is more likely to occur in the grains with low misorientation,and as load increases,the misorientation of twinned grains tends to be more random. |
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