Effect Of Nd On Microstructrue And Mechanical Properties Of Mg-Al-Zn Alloy

Improving microscopic structure mechanical properties of magnesium alloys by alloying become a hot topic. Rare earth is considered to be effective element to improve mechanical properties of magnesium alloys. At present, the researches about effect of Nd on Mg-Al alloys aren't quite perfect. So, it is very important to study the effect of Nd on microstructure and mechanical properties of Mg-Al alloys for developing new type magnesium alloys and expanding the using range of magnesium alloys.In this thesis, AZ80 and Mg-8.5Al-0.5Zn alloy were added with different content of Nd elements respectively. The microstructure structure and phase composition of the alloy were systematically investigated using the optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-Ray diffraction (XRD) and other instruments. The mechanical properties of the alloy were systematically investigated by tensile test, Brinell hardness test and other research methods. The relationship between the performance of magnesium alloy and Nd content was studied and analyzed by comparing the performance of Alloys with different Nd content. The improvements of Nd element to two kinds of matrix alloy were compared and analyzed.The results showed that:Nd addition can significantly improve the microstructure of AZ80 as well as Mg-8.5Al-0.5Zn alloy, and the Mg17Al12 phase of reticular formation was transformed into dispersed and fine bone shape, as well as results in formation of needle-like Al3Nd phase with high hardness and high melting point in magnesium alloy. There was one kind of new phase of Al-RE-Mn phase appeared in AZ80 alloy. Both the best refinement results of AZ80 and Mg-8.5Al-0.5Zn alloy were obtained when Nd addition was 1.0%. When add same amount of Nd content, the microstructure of AZ80-xNd alloy was finer than that of Mg-8.5Al-0.5Zn-xNd alloy.The addition of Nd element increases tensile strength of the two alloys at room and high temperature. When Nd element content was 1.0%, the tensile strength of as cast AZ80-xNd alloy and Mg-8.5Al-0.5Zn-xNd alloy reached 180MPa and 190MPa at room temperature, compared with the tensile strength of matrix alloy increased by 5.9% and 13.4%, respectively. The tensile strength of as cast alloys reached 159MPa and 160MPa at high temperature, compared with that of matrix alloy increased by 12% and 15.1%, respectively. The tensile strength improvement effect of Nd element on the Mg-8.5Al-0.5Zn alloy was obviously better than that on AZ80.After the addition of Nd element, both the plastic deformability of the two alloys were also improved. Both the most obvious improvement of plastic deformability of AZ80 and Mg-8.5Al-0.5Zn alloy were obtained when Nd element content was 1.0%. The elongation rate of AZ80-xNd alloy increased to 3.6% from 2.7% at room temperature, the rate of increase was 33.3%. The elongation rate of Mg-8.5Al-0.5Zn-xNd alloy increased to 4.0% from 2.9% at room temperature, the rate of increase was 37.9%. While at high temperature, when Nd element content was 1.0%, the elongation rate of AZ80-xNd alloy increased to 5.1% from 4.7%, the elongation rate increased by 8.5%; when Nd element content was 0.5%, the elongation rate of Mg-8.5Al-0.5Zn-xNd alloy increased to 5.2% from 5.0%, the elongation rate increased by 4%.The addition of Nd element can increases hardness of the two alloys. The Brinell hardness of AZ80 matrix alloy was HB 61.2, after adding Nd element the hardness increased significantly. When add 1.5% of the Nd elements, the Brinell hardness of alloy was HB 67.5. The Brinell hardness of Mg-8.5Al-0.5Zn alloy without Nd elements was HB 59.4, as the increase of Nd element addition, the hardness was improved continually. When the Nd element content was 1.5%, the Brinell hardness of the alloy was HB 65.9. In the range of Nd content researched in this project, the Brinell hardness of the alloy was improved with the increase of Nd content. The reasons can be attributed to:The addition of Nd element can refine the Mg17Al12 phase of the as-cast alloy, so the distribution is more diffuse, as well as results in formation of Al3Nd phase with high hardness.