Study On Preparation, Microstructures And Properties Of Magnesium Matrix Composites Under Physical External Fields

Particulate reinforced magnesium matrix composites have become the major research direction of magnesium matrix composites, due to the simple preparation technology, isotropic properties and secondary processing. However, the agglomeration tendency of particle increase with the decrease of the particle size, which can improves the strength of composite at the expense of ductility. Therefore, the further development and application of particulate reinforced magnesium matrix composites have been limited. In this paper, the electromagnetic field, ultrasonic field and compound field have been performed in the processing of TiB2/AZ31magnesium matrix composites respectively, and the effect of physical fields on the distribution of particle and microstructure and properties of composites have been studied. The main results are as follows:The TiB2/AZ31magnesium matrix composites were prepared by mechanically mixing and in-situ method, respectively. Compared with mechanically mixing method, the in-situ method can reduce the size of TiB2particle and improve the wettability between the particle and magnesium melt. Moreover the in-situ particle can increase the number of effective heterogeneous nucleation core, and the microstructure of composites can be further refined. But the in-situ TiB2particle in the matrix still aggregates severely.Ultrasonic energy decreases rapidly with the increase of propagation distance, which is mainly concentrated in the vicinity of ultrasonic probe. The clusters compose of in-situ TiB2particle at micro-nanometer scale can be broke, when ultrasonic acts on magnesium matrix composites melts. In a certain time range, with the extension of ultrasonic time, the size of particle clusters shows a decreasing tendency. In this working condition, the optimum processing parameters of ultrasonic treatment duration is25min. Electromagnetic stirring can refine the microstructure of TiB2/AZ31composites, and promote the uniformity of the distribution of TiB2particle clusters, but it has a smaller influence on the size of particle clusters.The compound field significantly refines the microstructure of the TiB2/AZ31composite, and promote the morphology ofβ-Mg17Al12vary from bone-like plates to lamellar precipitates. The helical magnetic stirring promotes the melt flowing through the area of ultrasonic probe, and enlarges the effective range of ultrasonic disintegration. In addition, the compound field decreases the size of the clusters of TiB2particle obviously and distributes them uniformly in the matrix.After the treatment of hot rolling, the AZ31magnesium alloy present obvious dynamic recrystallization, and the grain size of alloy is significantly refined. What’s more, shear zone compose of tiny grains will appear along the direction of hot rolling. With the introduction of TiB2particle and compound field, the shear zone of composites becomes narrower and denser. And the TiB2particle clusters in composites can be further broken by the flow stress of rolling and distribute along the streamline. The fracture morphology of composites under compound field has small cleavage plane and more tearing ridge and dimple. The comprehensive mechanical properties of TiB2/AZ31composites are evidently improved, and the values of tensile and yield strength and elongation are351MPa,315MPa and7.7%, respectively.