往复挤压Mg-4Al-2Si合金的显微组织与高温力学性能

研究了往复挤压Mg-4Al-2Si合金的显微组织与高温力学性能。结果表明,往复挤压可显著细化Mg-4Al-2Si合金的组织,随着挤压道次的增加,基体晶粒与Mg2Si相颗粒不断细化,其中,基体晶粒由于动态再结晶而细化。挤压8道次时,基体晶粒和Mg2Si颗粒的平均尺寸分别由铸态的45μm和20μm减小至1.5μm和1.3μm;但是,当挤压道次为11时,基体晶粒与Mg2Si相颗粒均出现粗化现象。往复挤压可使合金的高温力学性能大幅度提高,挤压8道次时,高温屈服强度最高,为197 MPa;挤压11道次时,高温抗拉强度最高,为256 MPa,与铸态高温强度相比,分别提高了163.9%和239.7%。合金的高温强化机制为Mg2Si颗粒的弥散强化作用,高温拉伸断裂形式为微孔聚合型韧性断裂。

Microstructure and elevated temperature mechanical properties of Mg-4Al-2Si alloy by reciprocating extrusion

The microstructure and elevated temperature mechanical properties of Mg-4Al-2Si(AS42)alloy by reciprocating extrusion(RE)were studied.The results show that the RE is an effective method to refine grain and Mg_2Si particles of AS42 alloy.As the number of RE passes is increased,the grain and particles become finer.The α-Mg grain refinement is mostly due to dynamic recrystallization.The grain sizes of as-cast α-Mg and Mg_2Si particles decrease from 45 μm and 20 μm to 1.5 μm and 1.3 μm after 8 passes RE,respectively.The grain and particles begin to coarse due to high temperature from 11 passes RE.The elevated temperature mechanical properties of AS42 alloy is improved significantly by RE.RE-8 passes,yield strength shows maximum,197 MPa.RE-11 passes,the maximum ultimate tensile strength 256 MPa is approached.The yield strength and ultimate tensile strength increase by 163.9% and 239.7% compared with as-cast AS42 at 150 ℃ respectively.Elevated temperature strengthening mechanism of RE-AS42 alloy is Mg_2Si particles dispersion strengthening.RE-AS42 alloy usually shows flexible fracture at 150 ℃.