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This study aims to examine the variation in corrosion characteristics and tensile properties of WE43 magnesium alloy in an actual marine atmospheric environment by means of outdoor exposure tests. The macroscopic corrosion morphology, microstructure, and tensile properties were analyzed. The results indicated that WE43 alloy will corrode rapidly during exposure under marine atmospheric environmental conditions, resulting in a loose and porous Mg(OH)2 layer on the surface. The Mg matrix was mainly consumed as an anode, leading to the occurrence of corrosion pits. With the increase in exposure time, both the tensile strength and plasticity of WE43 alloy gradually deteriorated. After exposure for six months, the elongation and area reduction were significantly reduced, with a reduction ratio of more than 50%. After 18 months of exposure, the ultimate strength of the alloy decreased from 359 MPa to 300 MPa. According to an analysis of fractures in the alloy, the corrosion pits on the sample surface were the main reason for the decrease in tensile properties. [ABSTRACT FROM AUTHOR]

For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope (OM), a scanning electron microscope (SEM), an energy dispersive spectroscope (EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present.

To obtain a spheroidal microstructure of a semi-solid Mg-Zn-Nd-Zr alloy, which is favorable for the subsequent thixocasting process, the recrystallization and partial remelting (RAP) method was used in this study, and the microstructure evolution of the alloy and the mechanism of the shape factor change during the RAP process were invesigated. The as-cast Mg-Zn-Nd-Zr alloy was prepared in a metal mold and then extruded into bars with an extrusion ratio of 16:1. Partial remelting was carried out on the extruded samples at 589 ℃ (at a heating rate of 0.5 ℃·s-1) for different holding times ranging from 0 to 90 min. To examine the effect of heating rate, partial remelting of samples at the heating rate of 2 ℃·s-1 was also performed. Results show that the extruded microstructure rapidly evolutes into recrystallized grains in the semi-solid state; the liquid film initially forms at grain boundaries during the partial remelting, and then gradually changes from continuous into discontinuous state with the increase of holding time; this results in the agglomeration of adjacent grains and the decrease in shape factor. The value of shape factor increases continuously with holding time at first and reaches the maximum 0.62 when holding for 60 min, while decreases rapidly after a prolonged holding time. Moreover, local melting, mainly due to the inhomogeneous deformation during extrusion, becomes more significant and less uniformly distributed at a relatively higher reheating rate. The Mg-Zn-Nd-Zr magnesium alloy components have been thixo-cast successfully using the RAP method, which strongly proves the feasibility of RAP process in Mg-Zn-Nd-Zr alloy.

To obtain a spheroidal microstructure of a semi-solid Mg-Zn-Nd-Zr alloy, which is favorable for the subsequent thixocasting process, the recrystallization and partial remelting (RAP) method was used in this study, and the microstructure evolution of the alloy and the mechanism of the shape factor change during the RAP process were invesigated. The as-cast Mg-Zn-Nd-Zr alloy was prepared in a metal mold and then extruded into bars with an extrusion ratio of 16:1. Partial remelting was carried out on the extruded samples at 589 °C (at a heating rate of 0.5 °C -s'1) for different holding times ranging from 0 to 90 min. To examine the effect of heating rate, partial remelting of samples at the heating rate of 2 °c-s~1was also performed. Results show that the extruded microstructure rapidly evolutes into recrystallized grains in the semi-solid state; the liquid film initially forms at grain boundaries during the partial remelting, and then gradually changes from continuous into discontinuous state with the increase of holding time; this results in the agglomeration of adjacent grains and the decrease in shape factor. The value of shape factor increases continuously with holding time at first and reaches the maximum 0.62 when holding for 60 min, while decreases rapidly after a prolonged holding time. Moreover, local melting, mainly due to the inhomogeneous deformation during extrusion, becomes more significant and less uniformly distributed at a relatively higher reheating rate. The Mg-Zn-Nd-Zr magnesium alloy components have been thixo-cast successfully using the RAP method, which strongly proves the feasibility of RAP process in Mg-Zn-Nd-Zr alloy. [ABSTRACT FROM AUTHOR]