Study On The Boron Rare Earth Magnesium Alloys

Magnesium alloy has excellent strength and stiffness ratio and can adapt to the requirement of structures on many occasions.In recent years, the research and application of magnesium alloy become a trend.Especially the rare earth element and boron element have a unique role in improving the performance of magnesium alloy. But these researches are mainly focused on the single effect of rare earth element and boron element in magnesium alloys.Therefore,the comprehensive study of boron and rare earth that is used to improve the performance of magnesium alloy material is one of the important development direction of magnesium alloy.This article is through alloying strengthening, deformation strengthening and other means to study the effect of boron and rare earth on magnesium alloy.It is of realistic significance for the development of a new type of high quality and inexpensive magnesium alloy with high mechanical properties.In this thesis, through the study of the three magnesium alloys Mg-Al-Ti-B2O3、 Mg-RE-B2O3、Mg-RE-KBF4, the solid solubility theory of the various elements in the magnesium was analyzed with the application of the binary alloy phase diagram. Specific analysis of the alloy were completed by orthogonal experimental design and Gibbs free energy alogrithm so that the proportion of the composition of the three kinds of alloy were determined, and the comparative experiments were carried out, respectively. At last, the optimal alloy was obtained.In the experiment of the Mg-Al-Ti-B2O3 alloy, the sample of the Mg-9Al-6Ti、 Mg-9Al-6Ti-3B2O3 and Mg-9Al-6Ti-6B2O3 were prepared. The optical metallography (OM), scanning electron microscopy (SEM), X-ray diffractometer and mechanical properties tests methods were adopted to study the effects of B2O3 to the microstructure and mechanical properties of Mg-9Al-6Ti alloy. With the addition of 3% B2O3,the average grain size of Mg-9Al-6Ti decreased from 54.8μm to 12μm, the precipitation of the Mg17Al12 phase decreased,the Al3Ti phase increased, besides, the new MgB6 and Ti3B4 phase occured.In the experiment of the Mg-RE-B2O3 alloy, the Mg-RE-B2O3 alloy casting and heat extruded samples were prepared. The optical metallography, scanning electron microscopy, X-ray diffractometer and mechanical properties test methods were adopted to study the effects and rules of the boron element in B2O3 to the microstructure uniformity of the metal substrate and the compactness of the materials. The results again proved that the hardness of the alloy increase with the addtion amount of the B2O3, the boron element improved the microstructure uniformity of the material substrate. In the Mg-RE-B2O3 alloy, the boron and lanthanum elements binded preferentially to precipitate LaB4 and LaB6 particles dispersed spread over in the alloy, which provide the strengthening mechanism to prepare the magnesium alloy with the tensile strength greater than 500Mpa. For the Mg-RE-B2O3 heat extruded samples, the tensile yield strength is more than 500Mpa, the elongation is 5%.In the experiment of the Mg-RE-KBF4 alloy, the orthogonal experimental design was applied to prepare 20 kinds of samples and seven alloy samples which showed high performance were selected. For these seven samples, the vivtorinox microhardness test, optical microscope, scanning electron microscope and energy spectrum analyzer were used to do quantitative analysis,the X-ray diffraction was used to do the material analysis,and the tensile test was carried out to verify the mechanical property at room temperature.All these tests help to comprehensively study the microstructure and mechanical hardness of the magnesium alloy. The results showed that La、Ce refined the microstructure of the alloy siginificantly. The hardness of the magnesium increased 57% with the addition amount of the mixed rare earth.This thesis finally stutied to make full use of the acivity of the magnesium and rare earth,boron and other elements in the molten state, and created a new Mg-RE-B2O3 alloy series. Focused on the role of boron, the method which made the process as simple as possible and the cost lowest was adopted to investigate the strengthing mechanism of the preparation of the magnesium alloy whose strength is more than 500Mpa. All these provided the theoretical basis for the production of low cost, high strength magnesium alloy materials and the future research directions for the magnesium alloy industry.