This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and trans...This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.展开更多
Friction stir brazing with ultrahigh rotation speed was applied to 6061 aluminium alloy–pure copper lap joints with the aid of zinc foil.The effects of different shoulder diameters from 7 to 15 mm on the microstructu...Friction stir brazing with ultrahigh rotation speed was applied to 6061 aluminium alloy–pure copper lap joints with the aid of zinc foil.The effects of different shoulder diameters from 7 to 15 mm on the microstructure and mechanical properties of Al/Cu FSB joints were investigated along with the temperature and resistance of the friction tool.The oscillation of forward resistance and lateral force was related to the flow of the plastic metal and contributed to obtain a good appearance during the welding process.From the appearance of the welded joints,it was obvious that the phase difference between the forward resistance and lateral force had a significant influence on the joint characteristics.Obvious scale-like ripples appeared on the weld area when a sharp angle in the phase difference curve existed.Additionally,with a lower axial force and oscillation assistance,a satisfactory joint could be obtained.The results of the shear strength of the brazed joint showed that the shoulder with a 12 mm diameter yielded the highest shear strength.Meanwhile,the zinc foil in the middle melted completely and formed finely dispersed CuZn5 Al–Zn eutectic structures at the Al–Cu interface.展开更多
在传统对称式电阻、电容、二极管RCD(resistance capacitance diode)箝位正激变换器基础上,通过引入中间电容和用开关管代替副边的一个二极管,提出了一种具有正反激功能的新型变换器。该变换器在继承传统对称式RCD箝位正-反激变换器的...在传统对称式电阻、电容、二极管RCD(resistance capacitance diode)箝位正激变换器基础上,通过引入中间电容和用开关管代替副边的一个二极管,提出了一种具有正反激功能的新型变换器。该变换器在继承传统对称式RCD箝位正-反激变换器的高效率、占空比可大于0.5和低开关管电压应力优点的同时,进一步拓宽输入电压变化范围和提高输出电压增益。首先分析了变换器工作于激磁电流连续导电模式MCCM(magnetizing current continuous mode)的工作过程,详细分析了MCCM和激磁电流断续导电模式MDCM(magnetizing current discontinuous mode)2种模式下的宽范围和增益特性以及原/副边开关管实现零电压转换ZVS(zero voltage switch)的条件;然后确立了在一定漏电感功率下箝位电阻值与箝位电容电压之间的函数关系曲线,并以此作为选取箝位电阻参考。最后,通过一台实验样机验证了理论分析的正确性。展开更多
基金supported by the National Key R&D Program of China (2022YFB3605500 and 2022YFB3605503)the National Natural Science Foundation of China (62074039 and 12004074)+1 种基金China Postdoctoral Science Foundation (2020M681141)the National Postdoctoral Program for Innovative Talents (BX20190070)。
基金supported by the National Natural Science Foundation of China (Nos. 51805358 and 51775366)Key Research and Development Program of Jinzhong (No. Y201023)College Students’ Innovative Entrepreneurial Training Plan Program (No. 202010112011)
文摘This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.
文摘Friction stir brazing with ultrahigh rotation speed was applied to 6061 aluminium alloy–pure copper lap joints with the aid of zinc foil.The effects of different shoulder diameters from 7 to 15 mm on the microstructure and mechanical properties of Al/Cu FSB joints were investigated along with the temperature and resistance of the friction tool.The oscillation of forward resistance and lateral force was related to the flow of the plastic metal and contributed to obtain a good appearance during the welding process.From the appearance of the welded joints,it was obvious that the phase difference between the forward resistance and lateral force had a significant influence on the joint characteristics.Obvious scale-like ripples appeared on the weld area when a sharp angle in the phase difference curve existed.Additionally,with a lower axial force and oscillation assistance,a satisfactory joint could be obtained.The results of the shear strength of the brazed joint showed that the shoulder with a 12 mm diameter yielded the highest shear strength.Meanwhile,the zinc foil in the middle melted completely and formed finely dispersed CuZn5 Al–Zn eutectic structures at the Al–Cu interface.
文摘在传统对称式电阻、电容、二极管RCD(resistance capacitance diode)箝位正激变换器基础上,通过引入中间电容和用开关管代替副边的一个二极管,提出了一种具有正反激功能的新型变换器。该变换器在继承传统对称式RCD箝位正-反激变换器的高效率、占空比可大于0.5和低开关管电压应力优点的同时,进一步拓宽输入电压变化范围和提高输出电压增益。首先分析了变换器工作于激磁电流连续导电模式MCCM(magnetizing current continuous mode)的工作过程,详细分析了MCCM和激磁电流断续导电模式MDCM(magnetizing current discontinuous mode)2种模式下的宽范围和增益特性以及原/副边开关管实现零电压转换ZVS(zero voltage switch)的条件;然后确立了在一定漏电感功率下箝位电阻值与箝位电容电压之间的函数关系曲线,并以此作为选取箝位电阻参考。最后,通过一台实验样机验证了理论分析的正确性。
