Abstract
A ZK61-Y magnesium (Mg) alloy wheel hub was prepared via liquid forging—isothermal forging process. The effects of Y-element contents on the microstructure and mechanical properties of liquid forging blanks were investigated. The formation order of the second phase was I-phase (Mg3Zn6Y) → W-phase (Mg3Zn3Y2) → Z-phase (Mg12ZnY) with the increase of the Y-element content. Meanwhile, the I-phase and Z-phase formed in the liquid forging process were beneficial to the grain refinement. The numerical simulation of the isothermal forging process was carried out to analyze the effects of forming temperature on the temperature and stress field in the forming parts using the software Deform-3D. Isothermal forging experiments and post heat treatments were conducted. The influence of isothermal forging temperature, heat treatment temperature and preservation time on the microstructure and mechanical properties of the forming parts were also studied. The dynamic recrystallization (DRX), second-phase hardening, and work hardening account for the improvement of properties after the isothermal forging process. The forming part forged at 380 °C displayed the outstanding properties. The elongation, yield strength, and ultimate tensile strength were 18.5%, 150 MPa and 315 MPa, respectively. The samples displayed an increased elongation and decreased strength after heat treatments. The 520 °C—1 h sample possessed the best mechanical properties, the elongation was 25.5%, the yield stress was 125 MPa and the ultimate tensile strength was 282 MPa. This can be ascribed to the recrystallization and the elimination of working hardening. Meanwhile, the second phase transformation (I-phase → W-phase → Mg2Y + MgZn2), dissolution, and decomposition can be observed, as well.
Highlights
As the crisis of resource and environment become more and more intensive, the requirement for energy conservation and emission reduction in transportation vehicles is growing insistently [1,2]
A ZK61-Y magnesium (Mg) alloy wheel hub was prepared via liquid forging-isothermal forging process
The max effective stress mainly concentrates on the center bottom of the forming part, where it is the critical point in the isothermal forging process
Summary
As the crisis of resource and environment become more and more intensive, the requirement for energy conservation and emission reduction in transportation vehicles is growing insistently [1,2]. The Mg alloys containing rare-earth elements are proposed, such as the Mg-Zn-Zr-Y alloys possessing higher strength, better plasticity, and corrosion resistance [6,7,8,9,10]. Kishida et al [11] prepared the Mg–Zn–Y ternary alloys containing highly-ordered. Takagi et al [12] performed micro-double-shear tests in the temperature range of 298 K–673 K to quantify the temperature dependence of prismatic slip in a long-period stacking ordered Mg85 Zn6 Y9. They found that the prismatic slips were promoted through cross-slip onto the basal plane over the transition temperature
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