Experimental Investigation And Thermod Ynamic Calculation Of Phase Relations In The Ca-Y、Mg-Ca-Y、Ce-Sr And Mg-Ce-Sr Systems

Mg alloys have some attractive properties,such as samll density, specific elastic modulus,high strength-to-weight ratio, good shock-absorbing,good heat dissipation, good corrosion resistance of organic matter, alkali and high impact load capacity than the aluminum alloy and other excellent characteristics. With the increasing shortage of energy and raw materials, as the basis of magnesium alloy phase diagram thermodynamics research is increasingly showing great application value. In the research and development of practical, due to the activity property and high evaporability of magnesium, the preparation of high quality magnesium alloy samples is an wordwild problem.We choosed the composition the key alloys by using thermodynamic calculation, all samples are pressed into a0.5cm diameter cylinder and then sealing in a Ta tube by means of powder metallurgy method. Because of the strong oxidizing of Ca, Y, Sr and Ce, all samples are prepared in a vacuum glove box. Combining X-ray powder diffraction (XRD), scanning electron microcopy (SEM) with energy dispersive X-ray spectroscopy (EDS) and differential scanning calorimetry (DSC) techniques, we investigated phase relationships of Ca-Y, Mg-Ca-Y, Ce-Sr and Mg-Ce-Sr systems. We deduced the Mg-Ca-Y and Mg-Ce-Sr phase diagram by comprehensive analysis all experimental results of this work. Basing on present own experimental data and reliable literature data in Ca-Y system, Ca-Y, Ce-Sr binary systems and Mg-Ca-Y, Mg-Ce-Sr ternary system were optimized by Calphad method. Our major work are present as follows:1). Investigated the Ca-Y binary phase diagram. No observed any binary compound in the system.2). The isothermal section of Mg-Ca-Y ternary system at400℃has been experimentally investigated. The results showed that no ternary compound was found in this isothermal section of Mg-Ca-Y ternary system. This isothermal section consists of7single-phase regions,11tow-phase regions and5three-phase regions. The maximum solid solubilities of Ca in Mg24Y5, Mg2Y and MgY are8.3at.%,15.4at.%and5.3at.%, respectively. The maximum solid solubilities of Y in Mg2Ca is12.4at.%.3). Investigated the Ce-Sr binary phase diagram. No observed any binary compound in the system.4). The isothermal section of Mg-Ce-Sr ternary system at400℃has been experimentally investigated. The results showed that no ternary compound was found in this isothermal section of Mg-Ce-Sr ternary system. This isothermal section consists of11single-phase regions,16tow-phase regions and9three-phase regions. The maximum solid solubilities of Sr in Mg12Ce, Mg41Ce5and MgCe are4.1at.%,3.6at.%and1.3at.%, respectively. The maximum solid solubilities of Ce in Mg17Sr2、Mg38Sr9、Mg23Sr6and Mg2Sr are3.4at.%,4.2at.%,3.7at.%and6.7at.%, respectively.5). Basing on the present experimental data and literature data, the thermodynamic optimization has been performed on the marginal Ca-Y and Ce-Sr binary systems and the Mg-Ca-Y and Mg-Ce-Sr ternary system. A good agreement between the calculated results and experimental data were obtain.It deserve to mentions that most of these systems are experimental investigated for the first time and a reasonable thermodynamic description were obtain for the first time also. The phase model used in these the systems are uniform which will benefit to unified into a big multi-components Mg alloys database. Our work provide a precious phase diagram information and thermodynamic description for the application and developing new Mg alloys.