Effects Of Sn And Ultrasonic Treatment On Microstructure And Mechanical Properties Of Mg-6Zn-0.5Y Magnesium Alloy

The purpose of this paper is to improve the mechanical properties of Mg-6Zn-0.5Y wrought magnesium alloys, especially the plasticity. The author employs two different approaches of alloying treatment and ultrasonic treatment to improve the organization and performance of the alloy. Optical metallographic microscope(OM), scanning electron microscope(SEM), energy dispersive X-ray spectrometer(EDS), X-ray diffraction analysis(XRD), and electronic universal testing machine were used to determine the best alloying Sn content and ultrasonic treatment power, and exploring the relationship between the microstructure and mechanical properties of the expepimental alloys treated by alloying treatment and ultrasonic treatment.Sn can obviously refine the as-cast microstructure of the experimental alloys, and the α-Mg matrix translated from dendrites to nearly equiaxed grains. But the grains tended to get coarsening when the Sn content increased to 4%. Sn mainly existed in the form of Mg Sn Y and Mg2 Sn phase. In addition, the tensile strength and elongation presented the trend of first increase and then decrease, and the alloy containing 1% Sn had the best elongation while the alloy containing 2% Sn had the best tensile strength, which were increased to 13.5% from 7.2%, and increased to 189 MPa from 110 MPa, improved by 87.5%, 71.8%, respectively. The principle of the alloy strengthening was due to grain refinement strengthening, solution strengthening and dispersion strengthening by adding Sn.After the homogenization treatment at 420℃ for 12 h, the Zn segregated in the grain boundary was basically eliminated, but not the Sn. The result of Mg-6Zn-0.5Y-2Sn homogenization treatment was the best. With the increase of Sn content, the homogenization treatment of ZM61-x Sn alloy get worse, the undissolved block compounds were Mg Sn Y and Mg2 Sn phase.After hot extrusion, the grains of Mg-6Zn-0.5Y-x Sn alloys were refined due to dynamic recrystallization. The unbroken compounds increased with the increase of Sn content. In addition, the tensile strength, yield strength and elongation presented the trend of first increase and then decrease with the increase of Sn content. The tensile strength increased apparently, a little the yield strength increased, and the elongation reached the maximum 14.8% when the Sn content was 1%, improved by 6.5%. The alloy containing 2%Sn had the tensile strength and yield strength, which were 312 MPa and 212 MPa, improved by 18.6%, 26.9%, respectively. However, the performances of the alloy get worse when the Sn content increased continuously, it was thought that the unbroken compounds were the main reasons.Ultrasonic treatment can significantly modify the as-cast microstructure of Mg-6Zn-0.5Y alloy, the refined degree was related to the ultrasonic power. The alloy prepared with 600 W ultrasonic treatment exhibited the best microstructure. With the application of ultrasonic treatment, the continuous I-phase at α-Mg boundaries was modified into discontinuous, and the area fraction of I-phase decreased with the increase of ultrasonic power. Besides, with the increase of ultrasonic power, the tensile strength and elongation presented the trend of first increase and then decrease. With 600 W ultrasonic treatment, the tensile strength and elongation of the as-cast alloy were the best. Compared to the untreated as-cast alloy, which were improved by 67.3%, 55.6%, respectively. It was thought that the disperse I-phase was the primary cause of the increased performance.