The effects of neodymium (Nd) and ytterbium (Yb) on the microstructures and tensile properties of Mg-5.5Zn-0.6Zr alloy were investigated. Results show that an addition of Nd or Yb both brings about the precipitation of a new γ (Mg, Nd) Zn2 or γ (Mg, Yb) Zn2 eutectic phase and results in a refinement in dendritics. However, the combination addition of Nd and Yb has an opposite effect on dendritics and leads to the formation of γ (Mg, Nd+Yb) Zn2 eutectic phases in the shape of network-like, even the lamellar eutectics are somehow thickened. After T4 solution treatment, the eutectic structure in Mg-5.5Zn-0.6Zr alloy is fully dissolved into the matrix while there are still some undissolved compounds at grain boundaries in Mg-5.5Zn-0.6Zr alloy with Nd and Yb addition. A new ternary phase Mg-Zn-Yb appears in Mg-5.5Zn-0.6Zr alloy containing Yb, which is formed at dendrite boundaries after solution treatment. The tensile test results indicate that the tensile strength, yield strength and the elongation are about 255.6 MPa, 163.6 MPa and 17.4%, respectively, at room temperature. This is mainly attributed to combined strengthening factors induced by Yb addition. At the elevated temperature, the Mg-5.5Zn-0.6Zr alloy with addition combination of Nd and Yb has a good performance in thermal stability, but inferiority in elongation.

Microstructures and mechanical properties of AM60 magnesium alloy with Sm addition were investigated through OM, SEM XRD and DNS100 electronic universal testing machines. The results show that the addition of Sm can refine grains, change the morphology and the size of beta-Mg17Al12 phase from continuous/discontinuous netlike or strip form to cobble or particulate form. The distribution also becomes homogeneous and dispersed, and obviously improves the microstructure. After Sm addition to the alloy, the dispersed, high-melting-point particles (mainly Al2Sm phase) are formed. With increasing of Sm content, the tensile strength and elongation of AM60 magnesium alloy increase first and then decrease. With addition of 1.0wt% Sm, the tensile strength and elongation of the alloy reach the maximum 210 MPa and 6.9%, respectively. The tensile fracture mechanism of AM60 magnesium alloy is changed from cleavage fracture to quasi-cleavage fracture with toughness characteristic.

Microstructures and mechanical properties of AM60 magnesium alloy with Sm and Ti addition were investigated through OM, SEM XRD and DNS100 electronic universal testing machines. The results show that the alloy grains can be rinfined by the addition of Sm and Ti.The morphology and distribution of beta-Mg17Al12 phase changed from continuous/discontinuous netlike or strip form to cobble or particulate form and even dispersed,respectively.The addition of Sm and Ti obviously improves the microstructure. There are some Al3Ti phase formed after the additon of Ti. Particle phase of Al2Sm,Mg41Sm5 and spherical phase of Al18Ti2Mg3 formed when the addition both of Sm and Ti. The Rod-shaped phase in the alloy dismissed or transformed roundly and massive particles become smaller after the inoculation of Ti and T-6 process subsequently. With addition of 1.0% Sm and 0.4%Ti both, the tensile strength and elongation reached 226MPa and 6.7% , elevated by 34.5% and 39.6% respectively;The heat tensile strength and elongation at 200 degrees C reached 170Mpa and 10.4%, elevated by 53.2% and 82.5% respectively. T6 process can further enhance the mechanical properties of AM(60).

To improve the strength, toughness, heat-resistance and deformability of magnesium alloy, the microstructure and mechanical properties of ZK60 alloy strengthened by Mg-Zn-Nd spherical quasi-crystal phase (I-phase) particles were investigated. Mg40Zn55Nd5 (I-phase) particles in addition to α-Mg, MgZn phase and MgZn2 phases can be obtained in ZK60-based composites under normal casting condition by the addition of quasi-crystal containing Mg-Zn-Nd master alloy. The experimental results show that the introduction of Mg-Zn-Nd spherical quasi-crystal phase into ZK60 alloy makes a great contribution to the refinement of the matrix microstructures and the improvement of mechanical properties. While adding Mg-Zn-Nd spherical quasi-crystal master alloy of 4.0wt.%, the ultimate tensile strength and yield strength of ZK60-based composite at ambient temperature reach their peak values of 256.7 MPa and 150.4 MPa, which were about 17.8% and 24.1% higher respectively than those of the ZK60 alloy. The improved mechanical properties are mainly attributed to the pinning effect of the quasi-crystal particles (I-phase) at the grain boundaries. This research results provide a new way for strengthening and toughening of magnesium alloys as well as a new application of Mg-based spherical quasi-crystals.

Filling and solidification process of permanent mold casting Mg or Al alloy tensile testing bar were simulated by the ProCAST software to understand various physical field and to optimize gating system design. The simulated results are well in agreement with experimental ones. The results verify that the optimized gating system can effectively eliminate casting defects in the testing bar so that mechanical properties of the permanent mold casting bar are nearly the true value.

In the present research, the Sb-alloying method was adopted, and the grain refinement and tensile properties of as-cast Mg-10Zn-5AI alloys with varying Sb addition were investigated. The results showed that with the Sb addition, a new phase (Mg 3Sb 2) of high melting point forms in the alloy beside the α-Mg matrix, τ-Mg 32(AI, Zn) 49 phase and φ-AI 2Mg 5Zn 2 phase. With an appropriate amount of Sb addition, the morphologies of the secondary phases and the matrix are changed and the grains are refined. When Sb addition is 0.6wt.%, both ambient and high temperature tensile strengths of the alloy reach their maximum. The hardness of the alloy increases with the increasing of Sb addition. With proper addition of Sb, the tensile failure mode of the alloy changes from cleavage fracture to quasi-cleavage fracture, showing good enhancement effect.

Factors that affect residual stress of tensile specimen such as pouring temperature,mold temperature and mold open time were analyzed by the methods of orthogonal test and numerical simulation.The results show that mold open time is the main factor that influences the residual stress.The residual stress can be reduced by adjusting the mold open time.Impact of mold temperature on the residual stress is less than that of mold open time,and the residual stress decreases with increasing of mold temperature.Residual stress is little affected by pouring temperature.

In the present research, the Sb-alloying method was adopted, and the grain refinement and tensile properties of as-cast Mg-10Zn-5Al alloys with varying Sb addition were investigated. The results showed that with the Sb addition, a new phase (Mg3Sb2) of high melting point forms in the alloy beside the α-Mg matrix, τ-Mg32(Al, Zn)49 phase and φ-Al2Mg5Zn2 phase. With an appropriate amount of Sb addition, the morphologies of the secondary phases and the matrix are changed and the grains are refined. When Sb addition is 0.6wt.%, both ambient and high temperature tensile strengths of the alloy reach their maximum. The hardness of the alloy increases with the increasing of Sb addition. With proper addition of Sb, the tensile failure mode of the alloy changes from cleavage fracture to quasi-cleavage fracture, showing good enhancement effect.