Ce添加对Mg-Ca挤压合金力学性能与热稳定性影响研究

Effect of Ce on Mechanical Property and Thermal Stability of Extruded Mg-Ca Alloy

目的 研究在Mg-0.2Ca挤压合金基础上分别添加质量分数为0.3%的Ce和0.6%的Ca后对合金的组织、力学性能和热稳定性的影响,探究Ce和Ca 2种合金元素对镁合金的强化和中高温条件下的稳定化效果。方法 首先,熔炼制备Mg-0.2Ca、Mg-0.2Ca-0.3Ce和Mg-0.8Ca 3种成分的合金;随后,对3种合金进行挤压变形,并对挤压合金组织和力学性能进行表征和测试;最后,在300℃下对3种合金进行等温退火,研究其组织演变过程和力学性能的衰减情况。结果 在Mg-0.2Ca合金基础上添加质量分数为0.3%的Ce可将挤压态合金再结晶分数由约92%降至约53%,再结晶晶粒尺寸由约1.64μm细化至约0.86μm,Mg-0.2Ca-0.3Ce三元合金的屈服强度可大幅提升至约364 MPa,该屈服强度与Mg-0.8Ca合金相当(约361 MPa),表明单位质量Ce的添加对强度提升的效果优于Ca。退火3 h后,Mg-0.2Ca-0.3Ce三元合金屈服强度的下降幅度约为124 MPa,显著低于Mg-Ca二元合金(约170 MPa)。以Mg-0.2Ca-0.3Ce合金为例进行静态再结晶组织演化分析表明,静态再结晶过程产生了稀土织构,其再结晶机制为不连续静态再结晶。结论 在Mg-0.2Ca挤压合金中添加质量分数为0.3%的Ce后,屈服强度由约307 MPa提升至约364 MPa,其强度与继续添加质量分数0.6%的Ca合金相当,Mg-Ca-Ce三元合金热稳定性优于Mg-Ca二元合金。

The work aims to investigate the effect of 0.3wt.% Ce and 0.6wt.% Ca on microstructure, mechanical properties and thermal stability of extruded Mg-0.2Ca alloy and explore the strengthening and stabilization effect of Ce and Ca on Mg alloy at medium and high temperature. Firstly, Mg-0.2Ca, Mg-0.2Ce-0.3Ce and Mg-0.8Ca alloys were melted and prepared. Then,the three alloys were extruded and the microstructure and mechanical properties of the extruded alloys were characterized and tested. Finally, the alloys were subject to isothermal annealing at 300 °C and their microstructure evolution process and decrease of mechanical properties were studied. Adding 0.3wt.% Ce to Mg-0.2Ca alloy reduced the recrystallization fraction of extruded alloy from about 92% to about 53% and the recrystallized grain size refined from about 1.64 μm to about 0.86 μm. The yield strength of Mg-0.2Ca-0.3Ce ternary alloy significantly increased to about 364 MPa, which was equivalent to that of Mg-0.8Ca alloy(about 361 MPa), indicating that Ce per unit mass had stronger strengthening effect than Ca. The yield strength of Mg-0.2Ca-0.3Ce ternary alloy decreased by about 124 MPa after annealing of 3 h, which was significantly lower than that of Mg-Ca binary alloy(170 MPa). With the Mg-0.2Ca-0.3Ce alloy as an example, static recrystallization microstructure evolution analysis revealed that the static recrystallization process produced rare earth texture, and its recrystallization mechanism was discontinuous static recrystallization(DDRX). In summary, adding 0.3wt.% Ce into extruded Mg-0.2Ca alloy increases yield strength from about 307 MPa to about 364 MPa, which is equivalent to the strength of 0.6wt.% Ca alloy. Mg-Ca-Ce ternary alloy has higher thermal stability than Mg-Ca binary alloy.