热处理诱导LPSO相析出对Mg-9Gd-2Nd-(1.5Zn)-0.5Zr合金性能的影响

Effect of Induction of LPSO Phase Precipitates by Heat Treatment on Properties of Mg-9Gd-2Nd-(1.5Zn)-0.5Zr Alloy

研究了热处理工艺对Mg-9Gd-2Nd-(1.5Zn)-0.5Zr合金组织和力学性能的影响,探索了LPSO相的形成机制。结果表明,铸态Mg-9Gd-2Nd-0.5Zr合金Ⅰ的组织由α-Mg基体和不规则条状第二相Mg_5RE组成,Zn元素加入使得铸态Mg-9Gd-2Nd-(1.5Zn)-0.5Zr合金Ⅱ中第二相转变为半连续网状(MgZn)_(3)RE相,体积分数增加,使得合金Ⅱ在525℃×5 h固溶后,第二相未能全部溶入基体中,同时晶内开始发生元素偏聚。随固溶时间延长至30 h(525℃),第二相固溶体积分数增加,晶内元素偏聚区形成了颗粒状析出相。之后随炉冷却至400℃保温4 h后,合金Ⅱ晶内析出大量的层片状LPSO相,晶内部分颗粒状相长大为针状相。综合对比确定Mg-9Gd-2Nd-(1.5Zn)-0.5Zr合金Ⅱ的最佳热处理工艺为525℃固溶处理30 h,炉冷至400℃保温4 h后水淬冷却至室温。热处理后的Mg-9Gd-2Nd-(1.5Zn)-0.5Zr合金Ⅱ对应的屈服强度、抗拉强度和伸长率分别为123.1 MPa、220.1 MPa和15.7%,塑性比固溶态Mg-9Gd-2Nd-0.5Zr合金Ⅰ大幅提升了91.5%。

The effect of heat treatment on the microstructure and mechanical properties of the Mg-9Gd-2Nd-(1.5Zn)-0.5Zr alloy and formation mechanism of LPSO phase was investigated. The results showed that the structure of as-cast Mg-9Gd-2Nd-0.5Zr alloy Ⅰ is composed of α-Mg matrix and irregular strip-like eutectic phase Mg_(5)RE. The addition of Zn element makes as-cast Mg-9Gd-2Nd-(1.5Zn)-0.5Zr eutectic phase of alloy Ⅱ transform into a semi-continuous network(MgZn)_(3)RE phase, and the volume fraction increased, so that after alloy Ⅱ was solid-dissolved at 525 ℃ for 5 h, the eutectic phase could not be completely dissolved into the matrix, and element segregation occurred in the crystal. With the prolongation of the solid solution time to 30 h(525 ℃), the volume fraction of the eutectic phase in solid solution increases, and the segregation zone of the elements in the crystal formed a granular precipitation phase. After cooling to 400 ℃ for 4 h in the furnace, a large number of lamellar LPSO phases were precipitated in the crystal of alloy Ⅱ, and part of the granular phase in the crystal was long needle-like phase. Comprehensive comparison determined that the optimal heat treatment process for Mg-9Gd-2Nd-(1.5Zn)-0.5Zr alloy Ⅱ was solution treatment at 525 ℃ for 30 h, furnace cooling to 400 ℃ for 4 h, water quenching and cooling to room temperature. The yield strength, tensile strength and elongation of the heat-treated Mg-9Gd-2Nd-(1.5Zn)-0.5Zr alloy Ⅱ are 123.1 MPa, 220.1 MPa and 15.7%, respectively, and the plasticity is 91.5% higher than the solid solution Mg-9Gd-2Nd-0.5Zr alloy I.