| The long period stacking ordered structure is a new reinforced phase in magnesium alloy, which increases mechanical properties of magnesium alloy at room temperature and high temperature greatly. Mechanical properties of cast alloy reinforced by long period structures are poor, because of the large grain and the uneven distribution of long periodic structure. The improvement of the solidification structure plays an important role in mechanical properties of magnesium alloy. Solidification under physical field has advantages of pollution-free, easy operation and so on, which is attached more and more importance by people. A single physical field can not meet the requirement of solidification. In order to give a better control on solidification structure of metals, compound field treatment technology has appeared. In this paper,effects of ultrasonic treatment, mechanical vibration treatment, compound treatment of ultrasonic and mechanical vibration, compound treatment of ultrasonic and pulsed magnetic field and compound treatment of mechanical vibration and pulsed magnetic field on solidified structure and mechanical properties of magnesium alloy Mg97Y2Cu1 by optical microscope(OM), scanning electron microscopy(SEM) with energy dispersive spectrum(EDS), X-ray and diffraction(XRD) were studied, respectively, and the related mechanism was also discussed. The major conclusions are as follows.1) Solidified structure and mechanical properties of Mg97Y2Cu1 alloy can be improved by ultrasonic treatment, mechanical vibration treatment, compound treatment of ultrasonic and mechanical vibration, compound treatment of ultrasonic and pulsed magnetic field and compound treatment of mechanical vibration and pulsed magnetic field during the course of solidification. Primary phase of alloy can be refined greatly,which degrades from developed dendrites into equiaxed or rosette-shaped crystal.Distribution of second phase becomes more uniform, its volume fraction along grain boundary also improves greatly. Compound treatment of ultrasonic and pulsed magnetic field or compound treatment of mechanical vibration and pulsed magnetic field combined with the effect of improving the solidification structure and mechanical properties of the alloy is better than that of a single physical field. Change law of mechanical properties of Mg97Y2Cu1 alloy is consistent with microstructure of Mg97Y2Cu1 alloy.2) When ultrasonic power is at 0~900W or treating time is at 0~120s, with theincrease of the ultrasonic power or the treating time, primary grain of the alloy refines at first and then coarsens, and the turning point is 700 W and 60 s, respectively. When vibration temperature is at 660~720℃, with the increase of the vibration temperature,primary grain of the alloy refines gradually. When the mechanical vibration amplitude voltage is at 0~300V, with the increase of amplitude voltage, primary phase of the alloy degrades and decreases gradually. When pouring temperature is at 660~750℃,with the increase of the pouring temperature, grain size of the alloy decreases firstly,then increases, and the turning point is 720 ℃. When the mold temperature is at20~600℃, with the increase of the mold temperature, grain size of the alloy increases at first, then decreases, and the turning point is 400℃. When ultrasonic power is 700 W and the treating time is 60 s, comprehensive mechanical properties of the alloy are the best. Tensile strength and elongation of the alloy are increased by up to 23.8% and105%, respectively, compared with the alloy in traditional condition. When the mechanical vibration amplitude voltage is 300 V, tensile strength and elongation of the alloy are increased by up to 84.5% and 158%, respectively, compared with the alloy in traditional condition.3) The content of Y and Cu in grain can be increased by compound treatment of ultrasonic and mechanical vibration. When vibration temperature is at 660~750℃ or mold temperature is at 20~600℃, with the increase of the vibration temperature or the mold temperature, solidified structure of the alloy refines at first and then coarsens,and the turning point is 720℃ and 200℃. When the vibration temperature is 720℃and the mold temperature is 200℃, tensile strength and elongation of the alloy are the highest, which is 172 MPa and 8.8%, respectively.4) When the vibration temperature is at 660~750℃ or the mold temperature is at20~600 ℃, with the increase of vibration temperature or the mold temperature,solidified structure of the alloy refines at first and then coarsens with compound treatment of ultrasonic and pulsed magnetic field, and the turning point is 720℃ and200℃. Under the condition of compound treatment of ultrasonic and pulsed magnetic field, tensile strength and elongation of the alloy are increased by up to 30.1% and119.6%, respectively, compared with the alloy in traditional condition, and Mg97Y2Cu1 alloy exhibits excellent high temperature mechanical properties.5) Under the condition of compound treatment of mechanical vibration and pulsed magnetic field, in the range of 0~400V or 0~10Hz, with the increase of voltage or frequency, grain size of the alloy decreases gradually. When pouring temperature is at650-750 ℃ or mold temperature is at 20-600 ℃, with the increase of the pouringtemperature or the mold temperature, solidified structure of the alloy coarsens at first and then refines, and the turning point is 690 ℃ and 400 ℃. Tensile strength and elongation of the alloy are increased by up to 23% and 117.4%, respectively, compared with the alloy in traditional condition. |
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