Effects Of Revolving Magnetic Field And RE On Microstructure And Properties Of Magnesium Alloy

Magnesium alloy, which has high specific strength and stiffness-weight ratio, is one of the most important light-weight and high-strength materials in the 21st century. However, the application of magnesium alloy is limited because of its inherent properties, such as low strength, poor corrosion resistance, high-temperature performance, and so on. With the development of aerospace, automotive, defense and electronics industry, the existing magnesium alloy cannot meet the special requirements. Therefore, it is important to explore active approach of improving the mechanical properties and formability, thus to push the application of magnesium alloy and develop its performance advantages. In this paper, the effects of revolving magnetic field combined with rare earth(RE) on microstructures, mechanical properties and corrosion behaviour of AZ91D were investigated.Microstructures of alloys were observed and studied by optical microscope, scanning electric microscope, energy spectrum analysis and X-ray diffraction. The results indicate that the effect of combined revolving magnetic field and RE caused a large decrease in grain size. In the case of 0.7% RE, when the exciting voltage, exciting time got the values of 80V, 3min respectively , the refine effect of AZ91D alloy was best. The average grain size of alloys reached the minimum, the homogenization degree of grain size increased significantly; theβ-Mg₁₇Al₁₂ phase changed from skeleton-like to discontinuous ones and there is a new needle-like Al₁₁RE₃ phase formed. The distribution of Al, Zn elements in the grain boundary decreases slightly while inside the grain increases slightly. Besides, the grain refinement mechanism was attributed to a more uniform temperature and solute field, which provided a higher nucleation rate and increased the effective grain growth restriction by RE element.Tensile and hardness tests show that the combined effect of revolving magnetic field and RE can significantly increased the hardness and mechanical properties of AZ91D alloy. The tensile strength has been enhanced remarkably while elongation has been improved with low values. With the increase of RE content, exciting voltage and exciting time, the macro-hardness, tensile strength and elongation have the similar trend-firstly increases to a maxmum value and then decreases. Under the influence of revolving magnetic field and RE, the fracture mechanism of AZ91D alloy has been changed from cleavage fracture to quasi-cleavage fracture. The strengthening and toughing mechanism of alloy perhaps included two factors: fine-grain strengthening and the change in size, shape and distribution of intermetallic compound. In the above factors, fine-grain strengthening plays a leading role.The effect of combining revolving magnetic field and RE on corrosion perfomance in 3.5%NaCl solution was studied by means of polarization curve measurement and static weight-loss test. The experiment found that combining revolving magnetic field and RE is beneficial to improve the corrosion resistance of AZ91D alloy. The research of corrosion mechanism discovered that the refinement of microstructure enhances the corrosion inhibition effect ofβ-Mg₁₇Al₁₂ phase and thus results in the improvement of corrosion resistance of alloys. And Al₁₁RE₃ compounds as a passivation of the cathode can reduce the microgalvanic current, which result in a further improvement of corrosion resistance.