Microstructure And Mechanical Properties Of Heat Resistant Mg-Al-La Alloys

In today's world, the problems of energy shortage,"energy conservation and emissions"have been attracting more and more extensive attentions from the governments. Therefore, the development of light-weight and high-performance magnesium alloys has became a very important part of industrial development. Magnesium alloy is the lightest metal structure material,and it also has a series of advantages,such as low proportion,high specific strength,good mechanical properties and processing properties,abundant reserves on earth etc.Therefore, putting this kind of alloy in application will bring significant benefits to the whole world. Magnesium alloys are widely used in the field of aviation, aerospace, 3C electronic products, especially in the field of automotive application. This paper studies the influence of single rare earth elements and different processing methods on the microstructure and mechanical properties of magnesium alloys. As a result,a new low-cost heat-resistant magnesium alloy of automobile application was developed.This experiment respectively acquire the AlLa42 (Mg-4Al-2La) alloy and AlLa45(Mg-4Al-5La) alloy via two kinds of process of "Permanent mold casting",and "High-process Die-casting". For the purpose of the study of microstructure and strengthening phase: the mechanical properties of alloy and stability of organization at high temperature were analyzed;the influence of different processing methods on microstructure and mechanical properties of alloy were found out; the influence of single rare earth element on microstructure and mechanical properties were researched; the change of microstructure and morphology of second phase under long time and high temperature heat treatment were demonstrated. The experimental results show that the mechanical properties of adding single rare earth element is more excellent than rich Ce mixed rare earth with the same processing method and rare earth content; the mechanical properties of AlLa45 alloy is more excellent than AlLa42 alloy with the same processing method; the mechanical properties of alloy made in High- process Die-casting is more excellent than which is made in Permanent mold casting with the same rare earth content. Because of high cooling speed in the process of High-pressure Die-casting,as a result, the grain is fine, it will prevent the grain boundary sliding effectively. Therefor,the strength of the alloy made in High- process Die-casting is higher than the alloy made in Permanent mold casting. There are more second phases in the alloy while the content of rare earth is higher, and it will prevent the grain boundary sliding effectively, so the strength of the AlLa45 alloy is higher than the AlLa42 alloy. After heat treatment (200? and 400? ) , the second phase morphology of alloy is changed from needle to blocky with the extension of heat treatment time. According to the result of X-ray diffraction and energy spectrum analysis,the needle and blocky phase are composed of Al element and La element before and after heat treatment, and the proportion is approximately close to 11:3. Therefore, there is only the change of the morphology of the second phase without the change of element compositions.By adding single rare earth element of La instead of rich Ce mixed rare earth, and analyzing the change of microstructure and morphology of second phase of alloy under heat treatment of long time and high temperature. Thus we developed a new type alloy of AlLa45 heat resisting Magnesium alloy. Compared with the AE44 alloy developed by Hydro Magnesium company, AlLa45 alloy has more excellent mechanical performance and heat resistance performance, so the applications of Magnesium alloy are wider in heat-resistant parts of automotive.