The precision width control is vital for product quality and production economy in plate width control process,so short stroke control method was used in plate rolling by opening or closing edger gap so as to avoid head end necking.Head end necking on different broadening ratio was analyzed,and sections of different elongations at edger rolling was calculated;based on the law of volume constancy,the adjustment functions were described by parabolic functions.Control curves were developed with three Gaussian curves by means of additional combining;SSC control curve was changed with different weights of those curves,w_1effect one-third of SSC length,w_2effect two-third of SSC length,w_3effect all three parts of SSC length.In order to adjust the amount of weights for precise quantification,PSO algorithm was used to build sufficiency function so as to obtain best rectangular degree by global optimization.Practical applications showed that the method proposed is available to improve the product rolling yields by 1.0%-2.0%and worthy to apply to plate rolling.
DP780 steel sheets consisting of ferrite and martensite were successfully friction stir spot welded(FSSW)at the rotation rates of 500 to 1500 r/min using a W-Re alloy tool.The effect of rotation rate on microstructure and mechanical properties of the FSSW DP780 was investigated.The peak temperatures in the welds at various rotation rates were identified to be above A3temperature.FSSW caused the dynamic recrystallization in the stir zone(SZ),thereby producing the fine equiaxed grain structures.At the higher rotation rates of≥1000 r/min,a full martensitic structure was observed throughout the SZs,whereas at the lower rotation rate of 500 r/min,the SZ consisted of a fine dual phase structure of ferrite and martensite due to the action of deformation induced ferrite transformation.The maximum average failure load as high as 18.2 k N was obtained at the rotation rate of 1000 r/min and the fracture occurred at the thinned upper sheet.
Friction stir welding (FSW) of Mg-Zn-Y-Zr plates with 6 mm in thickness was successfully carried out under a wide range of rotation rates of 600-1200 r/min with a constant traverse speed of 100 mm/min. After FSW, the coarse grains in the parent material (PM) were changed into fine equiaxed recrystallized grains at the nugget zone (NZ). Furthermore, the coarse Mg-Zn-Y particles (W-phase) were broken up and dispersed homogenously into the Mg matrix. With increasing rotation rates, the size of the W-phase particles at the NZ significantly decreased, but the recrystallized grain size tended to increase. The hardness values of the NZs for all the FSW joints were higher than those of the PM, and the lowest hardness values were detected in the heat affected zone (HAZ). The fracture occurred in the thermo-mechanical affected zone (TMAZ) on the advancing side for all the FSW joints in the tensile test, due to the incompatibility of the plastic deformation between the NZ and TMAZ caused by remarkably different orientation of grains and W-phase particles. The strength of FSW joint reaches 90% of that of its PM.
As-extruded ZK60 and ZK60-Y magnesium alloy plates were successfully processed via friction stir processing(FSP) at a tool rotation rate of 1600 r/min and a traverse speed of 200 mm/min. FSP resulted in the formation of equiaxed recrystallized microstructures with the average grain sizes of w8.5 and w4.7 mm in the ZK60 and ZK60-Y alloys, respectively. Moreover, FSP broke and dispersed the MgZn2 and W-phase(Mg3 Zn3 Y2) particles and dissolved MgZn2 phase in the FSP ZK60 alloy. With the addition of rare earth element yttrium(Y) into the ZK60 alloy, the ratio of the high angle grain boundaries(HAGBs) in the FSP alloys increased from 64% to 90%, and a certain amount of twins appeared in the FSP ZK60-Y alloy. The maximum elongation of 1200% and optimum strain rate of 3 103s1achieved at 450 C in the FSP ZK60-Y alloy were substantially higher than those of the FSP ZK60 alloy. This is attributed to the fine grains with high ratio of HAGBs and the distribution of a large number of dispersed second phase particles with high thermal stability in the FSP ZK60-Y alloy. Grain boundary sliding was identified as the primary deformation mechanism in the FSP ZK60 and ZK60-Y alloys from the superplastic data analyses and surficial morphology observations.
