The microstructures and mechanical properties of cast Mg-Zn-Al-RE alloys

The microstructures and mechanical properties of cast Mg-Zn-Al-RE alloys with 4 wt.% RE and variable Zn and At contents were investigated. The results show that the alloys mainly consist of alpha-Mg, Al2REZn2, Al4RE and tau-Mg-32(Al,Zn)(49) phases. and a little amount of the beta-Mg17Al12 phase will also be formed with certain Zn and At contents. When increasing the Zn or At content, the distribution of the Al2REZn2 and Al4RE phases will be changed from cluster to dispersed, and the content of tau-Mg-32(Al,Zn)(49) phase increased gradually. The distribution of the Al2REZn2 and Al4RE phases, and the content of beta- or tau-phase are critical to the mechanical properties of Mg-Zn-Al-RE alloys.

Microstructure and Strengthening Mechanism of Die-Cast Mg-Gd Based Alloys

Mg-8Gd-2Y-Nd-0.3Zn (wt%) alloy was prepared by the high pressure die-cast technique. The microstructure, mechanical properties in the temperature range from room temperature to 573 K, and strengthening mechanism were investigated. It was confirmed that the Mg-Gd-based alloy with high Gd content exhibited outstanding die-cast character. The die-cast alloy was mainly composed of small cellular equiaxed dendrites and the matrix. The long lamellar-shaped stacking compound of Mg3X (X: Gd, Y, Nd, and Zn) and polygon-shaped.

Structure stability and strengthening mechanism of die-cast Mg-Gd-Dy based alloy

Mg-8Gd-1Dy-0.3Zn (wt.%) alloy was prepared by high-pressure die-casting technique. The thermal stability, mechanical properties at temperature range from room temperature to 573 K and strengthening mechanism was investigated. The results showed that the die-cast state alloy was mainly composed of fine cellular equiaxed grain. The fine porosity-free skin region was related to the aggregation of rare earth elements. The long lamellar-shaped stacking compound containing Zn and polygon-shaped precipitate were observed along the grain boundaries. The die-cast sample exhibited high mechanical properties and good thermal stability until 523 K.

新型绿色荧光体ABLa(PO_4)_2:Ce, Tb研究(A = K, Na; B = Mg, Zn)

本工作完成了磷酸盐化合物ABLa(PO_4)_2的合成，这些磷盐均可在900 ℃左右合成；对其进行了结构测试与表征，发现这些磷酸盐属于单斜晶系独居石结构，与LaPO_4同构，具有很相近的晶胞参数；系统地研究了RE~(3+)离子(RE = Ce,Tb,Dy)在ABLa(PO_4)_2基质中的发光与能量传递规律，研究了Ce~(3+)、Tb~(3+)离子发光中心与基质晶格之间的相互作用，计算了这些稀土离子之间能量传递的临界距离Rc(dd)，结果表明ABLa(PO_4)_2基质中Ce~(3+)离子与基质晶格之间的相互作用属于中等程度耦合，Tb~(3+)离子与基质晶格之间的相互作用属于无辐射多声子过程，Ce~(3+)→Ce~(3+)、Ce~(3+)→Tb~(3+)能量迁移临界距离均与LaPO_4中相近，Ce~(3+) → Ce~(3+)相对于Ce~(3+) → Tb~(3+)属于快过程，Ce~(3+) → Ce~(3+)能量传递对ABLa(PO_4)_2:Ce,Tb荧光体的Tb~(3+)绿色发光起了重要的作用，ABLa(PO_4)_2基质是Ce~(3+)，Ce~(3+)-Tb~(3+)，Ce~(3+)-Dy~(3+)的优良发光基质；最后探讨了绿色荧光体ABLa(PO_4)_2:Ce，Tb的调制途径，主要研究了Ce~(3+)、Tb~(3+)离子的浓度效应，掺杂B_2O_3、Dy~(3+)、SiO_2对荧光体发光的影响及NH_4Cl的作用，结果表明Ce~(3+)、Tb~(3+)离子的适宜浓度分别为0.2～0.5和0.08～0.2，掺杂适量的B_2O_3、Dy~(3+)能很好地提高荧光体的发光，掺杂SiO_2、NH_4Cl不利荧光体发光。

Electrochemical corrosion behavior of cast Mg-Al-RE-Mn Alloys in NaCl solution

The electrochemical corrosion behavior of Mg-6Al-0.4Mn and Mg-6Al-4RE-0.4Mn (RE = Mischmetal) alloys is investigated in 3.5% NaCl solution. The results of corrosion process, polarization behavior, and electrochemical impedance spectroscopy of the alloys reveal that Mg-6Al-4RE-0.4Mn exhibits enhanced corrosion resistance. The addition of RE stabilizes the solid solution and modifies the passive film through a finer microstructure.

The effect of La or Ce on ageing response and mechanical properties of cast Mg-Gd-Zr alloys

Mg-8Gd-0.6Zr-1RE (RE = La or Ce, wt.%) alloys were prepared by casting. The microstructures, age hardening behavior and mechanical properties were investigated. The results show that the addition of 1 wt.% La or Ce to a Mg-8Gd-0.6Zr alloy reduces the dendrite arm spacing and slightly improves the mechanical properties and age hardening response.

Microstructure and mechanical properties of Mg-4.5Zn-xNd (x=0, 1 and 2, wt%) alloys

Microstructure and mechanical properties of Mg-4.5Zn-xNd (x = 0, 1 and 2, wt%) alloys heat-treated at 603 K for 2 It have been investigated. T-phase (an Mg-Zn-Nd ternary phase) was observed in the Nd containing alloys. The optimal mechanical properties were obtained in the Mg-4.5Zn-1Nd alloy, and the ultimate tensile strength and yield strength were 228 and 79 MPa, respectively. Through comparing with the Mg-4.5Zn alloy, the increments of ultimate tensile strength and yield strength were 51 and 17 MPa.

Effect of Nd on the microstructure, mechanical properties and corrosion behavior of die-cast Mg-4Al-based alloy

Die-cast Mg-4Al-0.4Mn-xNd(x = 0, 1, 2, 4 and 6 wt.%) magnesium alloys were prepared successfully and influences of Nd on the microstructure, mechanical properties and corrosion behavior of the Mg-4Al-0.4Mn alloy have been investigated. The results showed that with the addition of Nd binary Al2Nd phase and Al11Nd3 phase. which mainly aggregated along the grain boundaries, were formed, and the relative ratio of above two phases was in correlation with the Nd content in the alloy. Meanwhile, the grain sizes were greatly reduced with the increasing Nd content. It was found that due to the addition of Nd both the tensile properties and corrosion resistance were improved substantially.

Micro structures, tensile properties and corrosion behavior of die-cast Mg-4Al-based alloys containing La and/or Ce

In order to study the properties of Mg-Al-RE (AE) series alloys, the Mg-4Al-4RE-0.4Mn (RE= La, Ce/La mischmetal or Ce) alloys were developed. Their microstructures, tensile properties and corrosion behavior have been investigated. The results show that the phase compositions of Mg-4Al-4La-0.4Mn alloy consist of alpha-Mg and Al11La3 phases. While two binary Al-RE (RE = Ce/La) phases, Al11RE3 and Al2RE, are formed in Mg-4Al-4Ce/La-0.4Mn alloy, and Al11Ce3 and Al2Ce are formed in Mg-4Al-4Ce-0.4Mn alloy.

Microstructures and mechanical properties of as-cast Mg-5Y-3Nd-Zr-xGd (x=0, 2 and 4 wt.%) alloys

Mg-5Y-3Nd-0.6Zr-xGd (x = 0, 2 and 4 wt.%) alloys were prepared by metal mould casting technique, the structures and mechanical properties were investigated. The alloys were mainly composed of alpha-Mg solid solution and beta-phase. With increasing Gd content, Mg5RE phase increased and the grain was refined. The Mg-5Y-3Nd-2Gd-0.6Zr alloy exhibited highest ultimate tensile strength and Mg-5Y-3Nd-0.6Zr alloy showed highest yield strength at room temperature. With increasing amount of Gd, the thermal resistance was improved. The Mg-5Y-3Nd-4Gd-0.6Zr alloy exhibited highest UTS and YS at 250 degrees C, they were about 1.27 times higher than those of Gd-free alloy, which was mainly attributed to the increase of the beta-phase and Mg5RE strengthening phase.

Effect of substituting cerium-rich mischmetal with lanthanum on microstructure and mechanical properties of die-cast Mg-Al-RE alloys

Die-cast Mg-4Al-4RE-0.4Mn (RE = Ce-rich mischmetal) and Mg-4Al-4La-0.4Mn magnesium alloys were prepared successfully and their microstructure, tensile and creep properties have been investigated. The results show that two binary Al-RE phases, Al11RE3 and Al2RE, are formed along grain boundaries in Mg-4Al-4RE-0.4Mn alloy, while the phase compositions of Mg-4Al-4La-0.4Mn alloy mainly consist of alpha-Mg phase and Al11La3 phase. And in Mg-4Al-4La-0.4Mn alloy the Al11La3 phase occupies a large grain boundary area and grows with complicated morphologies, which is characterized by scanning electron microscopy in detail. Changing the rare earth content of the alloy from Ce-rich mischmetal to lanthanum gives a further improvement in the tensile and creep properties, and the later could be attributed to the better thermal stability of Al11La3 phase in Mg-4Al-4La-0.4Mn alloy than that of Al11RE3 phase in Mg-4Al-4RE-0.4Mn alloy.

Microstructures, mechanical properties and corrosion behavior of high-pressure die-cast Mg-4Al-0.4Mn-xPr (x=1, 2, 4, 6) alloys

Mg-4Al-0.4Mn-xPr (x = 1, 2, 4 and 6 wt.%) magnesium alloys were prepared successfully by the high-pressure die-casting technique. The microstructures, mechanical properties, corrosion behavior as well as strengthening mechanism were investigated. The die-cast alloys were mainly composed of small equiaxed dendrites and the matrix. The fine rigid skin region was related to the high cooling rate and the aggregation of alloying elements, such as Pr. With the Pr content increasing, the alpha-Mg grain sizes were reduced gradually and the amounts of the Al2Pr phase and All, Pr-3 phase which mainly concentrated along the grain boundaries were increased and the relative volume ratio of above two phases was changed. Considering the performance-price ratio, the Pr content added around 4 wt.% was suitable to obtain the optimal mechanical properties which can keep well until 200 degrees C as well as good corrosion resistance. The outstanding mechanical properties were mainly attributed to the rigid casting surface layer, grain refinement, grain boundary strengthening obtained by an amount of precipitates as well as solid solution strengthening.

Microstructure, tensile properties, and creep behavior of high-pressure die-cast Mg-4Al-4RE-0.4Mn (RE = La, Ce) alloys

High-pressure die-cast (HPDC) Mg-4Al-4RE-0.4Mn (RE = La, Ce) magnesium alloys were prepared and their microstructures, tensile properties, and creep behavior have been investigated in detail. The results show that two binary Al-Ce phases, Al11Ce3 and Al2Ce, are formed mainly along grain boundaries in Mg-4Al-4Ce-0.4Mn alloy, while the phase composition of Mg-4Al-4La-0.4Mn alloy contains only alpha-Mg and Al11La3. The Al11La3 phase comprises large coverage of the grain boundary region and complicated morphologies. Compared with Al11Ce3 phase, the higher volume fraction and better thermal stability of Al11La3 have resulted in better-fortified grain boundaries of the Mg-4Al-4La-0.4Mn alloy. Thus higher tensile strength and creep resistance could be obtained in Mg-4Al-4La-0.4Mn alloy in comparison with that of Mg-4Al-4Ce-0.4Mn. Results of the theoretical calculation that the stability of Al11La3 is the highest among four Al-RE intermetallic compounds supports the experimental results further.

Structure and mechanical properties of Mg-Zn-RE system alloys

The lightest density of Mg has stimulated renewed interest in Mg based alloys for applications in the automotive, aerospace and communications industries. However, Mg in the pure form has relatively low strength, limited ductility and is susceptible to corrosion. Great efforts have been made to improve the mechanical properties of Mg alloys. Alloying Mg with other elements is one of the most important methods. An important class of Mg alloys is the Mg-Zn-RE system (RE = rare earth elements). In recent few decades, a series of new Mg-Zn-RE system alloys have been obtained, and detailed the structure and mechanical properties of the alloys. In this paper, the structure and mechanical properties of the Mg-Zn-RE alloys have been summarized. It showed that these alloys have high strength and they are prospected to be widely used in the future.

Microstructures and properties of melt-spun and as-cast Mg-20Gd binary alloy

Mg-20Gd(%, mass fraction) samples were prepared using melt-spinning and copper mold casting techniques. Microstructures and properties of the Mg-20Gd were investigated. Results show that the melt-spun ribbon is mainly composed of supersaturated alpha-Mg solid solution phase and the as-east ingot mainly contains alpha-Mg solid solution and Mg5Gd phase. The differential scanning calorimeter (DSC) curve of the ribbon exhibits a small exothermic peak in the temperature range from 630 to 680 K, which indicates that the ribbon contains a metastable phase (amorphous). Tensile strength at room temperature of the melt-spun ribbon and as-cast specimen are 308 and 254 MPa, respectively. The elongations of the two samples are less than 2%. The fracture surfaces demonstrate that the fracture mode of the as-cast Mg-20Gd is a typical cleavage fracture and that of the melt-spun sample is a combination of brittle fracture and ductile fracture.