| Magnesium alloy has been extensively applied to many kinds of field including automobile, electron, aviation and aerospace due to its light weight and high specific strength, and was considered as the most lightweight construction materials worthy to be developed in 21th century. However, low strength feature of magnesium alloy has become a major drawback of its application. Grain refinement is one of important way to improve its mechanical properties because of lack of effective precipitation strengthening phase. Many researches had shown that the solidification microstructure could be refined notably after its metal melt after treated by ultrasonic field, so that ultrasonic field has a bright future in microstructure refinement.In this paper, macrostructure and microstructure, feature of precipitation phases, mechanical properties of AZ and AS magnesium alloys were investigated their melts treated by the continuous and the pulse ultrasonic fields through optical microscope, X-ray diffraction analysis, energy spectrum analysis, Leica analyze software, SEM (SEDX) and so on. The major conclusions were summarized as following:(1) The solidification microstructures of magnesium alloys could be refined obviously after their melts treated by the continuous or the pulse ultrasonic field. The effect of ultrasonic treatment is related with the parameters of the applied ultrasonic filed including the ultrasonic power (intensity), the treating time, the treating temperature, and the pulse width and the pulse period of the pulse ultrasonic field.(2) The better microstructures with refine grains of AZ80 magnesium alloys could be obtained after their melt was treated by the continuous ultrasonic field in the condition of high-power for short time or low-power for long time. And for AS41 alloy, there is an optimum value of power or intensity, and the refinement effect improved continuously as prolonging treating time when the power (or intensity) is 100W (or 14.1W/cm2). The Mg2Si phase in AS41 alloy was refined continuously while increasing the ultrasonic power, however, it seems that the there is a threshold value for treating time.(3) The effects of ultrasonic power, treating time and treating temperature on the microstructures of magnesium alloys as applying the pulse field to their melts were similar to those of continuous field. Because the wide width or short period of the pulse ultrasonic field is equivalence to high time average power, the effect of increasing width or shortening period of pulse filed is the same as the result of increasing apparent power.(4) The lattice parameters of phases in magnesium alloys could be changed obviously while their melts were ultrasonic treated. As prolonging treating time or increasing the pulse ultrasonic power, the lattice parameters ofβ-Mg17Al12 in AZ80 alloy reduce first and then increase; and the effects on the lattice parameters of Mg2Si in AS41 alloy have the same results.(5) As AZ80 magnesium alloy melt was treated by ultrasonic field, the mechanical properties of its cast alloy were improved greatly. |
