Microstructures and tensile properties of AZ31 magnesium alloys with the same amount of Ca and RE (Gd+La) additions are investigated. The results show that Al2Ca new phases form after adding Ca elements, Al2Gd and Al11La3 new phases form after adding Gd and La elements, and formations of Al-Ca and Al-RE phases could decrease Mg17Al12 phases and refine grains. Al2Ca and Al11La3 phases are crushed into granules because of severe deformation during hot extrusion, while Al2Gd phases are not. Room temperature (TR) and 150℃ (T150℃) tensile tests results reveal that both AZ31-1.5Ca and AZ31-1.5RE as-extruded alloys exhibit superior comprehensive tensile properties when compared to AZ31 as-extruded alloy, however, AZ31-1.5Ca as-extruded alloy could be a better choice in view of the costs. Textures images of as-extruded alloys indicate that 1.5wt.% Ca and RE additions affects little on textures of AZ31 as-extruded alloy, therefore, morphologies of second phases and average grain sizes are the leading cause of tensile properties of as-extruded alloys.

In this paper, the effect of Ca and Zr additions on microstructure and mechanical properties at room temperature of Mg-Sn alloys was investigated by comparison of Mg-3Sn (wt.%) (T3), Mg-3Sn-1Ca (wt.%) (TX31), and Mg-3Sn-1Ca-1Zr (wt.%) (TXK311) alloys under extrusion. The results show that the main phases of as-extruded T3 alloy were α-Mg and Mg₂Sn phases, while the CaMgSn phase was formed and the precipitation of Mg₂Sn phase was inhibited in the TX31 and TXK311 alloys due to the addition of the Ca element. Zr did not form intermetallic compounds with other elements but dissolved in the grains of the matrix and became nucleating particles. Incomplete dynamic recrystallization (DRX) occurred in all alloys during hot extrusion. The coarse rod-like and fine block-like mixed CaMgSn phase was observed in α-Mg matrix of as-extruded samples of the TX31 alloy, and the dispersed granular CaMgSn phase was observed in the TXK311 alloy. Ca inhibited the dynamic recrystallization behavior of the alloys, while Zr promoted the dynamic recrystallization behavior. All the as-extruded alloys exhibit typical fiber texture of {0001} basal//ED. With the addition of Ca and Zr elements, the particle stimulated nucleation (PSN) effect excited by the second phase particles gradually weakened the texture. TXK311 alloy has good comprehensive mechanical properties at room temperature, with tensile strength, yield strength, and elongation of 261 MPa, 244 MPa, and 11%, respectively, and the average grain size was 1.8 μm. Grain refinement and second phase dispersion strengthening are considered to play critical roles in the strength optimization of the TXK311 alloy.

The effects of Zn and Cu addition on the microstructure and mechanical properties of the extruded Mg-3Sn-1Ca alloy were systematically studied. The effects of the grain size, texture, type and distribution of the second phase on the mechanical properties of the alloy were analyzed. The mechanical test results show that the addition of Zn and Cu elements can significantly improve the mechanical properties of the alloy. The as-extruded Mg-3Sn-1Ca-1Zn-1Cu alloy has the best comprehensive mechanical properties, and the UTS, YS and E_L are 244 MPa, 159 MPa and 13.4%, respectively. Compared with the Mg-3Sn-1Ca alloy, the UTS and E_L of the Mg-3Sn-1Ca-1Zn alloy are increased by 50 MPa and 132%, respectively. However, the UTS of the TXC311 alloy is increased by 55 MPa, but the ductility of the Mg-3Sn-1Ca-1Cu alloy is far less than that of the Mg-3Sn-1Ca-1Zn alloy, which is mainly attributed to the presence of a large amount of hard and brittle Mg2Cu phase in the alloy. Interestingly, the addition of Zn to Mg-3Sn-1Ca-1Cu alloy can improve the elongation of the alloy, which is due to the solid solution strengthening caused by the Zn element and the formation of small MgZnCu phase with Zn element and the consumption of Mg2Cu phase.

Changes of precipitates, dynamic recrystallization, texture, and properties at room temperature in the as-extruded AZ alloys (Al = 0, 3, 6, 8, wt.%) with 0.3% La addition were systematically investigated in this work. The analysis results suggest that new Mg₁₂La with lamellar-structure precipitates in AZ01-0.3La alloy and new Al₁₁La₃ with needlelike structure precipitates in AZ-0.3La alloy with 3%–8% Al. Crashed Mg₁₇Al₁₂ could decrease the recrystallization temperature. Proper-sized Mg₁₂La and Al₁₁La₃ could promote the dynamic recrystallization nucleation, leading to the reduction of grains in the as-extruded AZ-0.3La alloy, except for 6% Al. At room temperature, the strength of as-extruded AZ-0.3La alloys increases as Al increases, and the elongation first increases and then decreases, while the elongation is greater than 20% with 3%–8% Al. Due to the refined average grain size of 12.2 μm, the scattered and wakened base texture, the as-extruded AZ31-0.3La shows the best comprehensive tensile property compared with other AZ-0.3La alloys and AZ alloys, of which the R_p0.2 is 162 MPa, the R_m is 252 MPa, and the A is 21.7%.