冷却速度对Mg-5Al-0.5Y合金组织和性能的影响

利用光学显微镜、扫描电镜、X射线衍射仪和硬度测试仪等试验手段,研究了金属型、石墨型及砂型铸造Mg-5Al-0.5Y合金分别在冷却速度为200、150和60℃/min时的微观组织和硬度的变化,并对其机理进行分析。结果表明,随着冷却速度的降低,α-Mg晶粒粗化,晶粒平均尺寸从52.83μm增大到68.96μm,增幅30.53%,而离异共晶β-Mg17Al12相从连续网状分布变为粗大的断续分布,相对含量也由10.35%减少至8.67%,降幅为16.23%;冷却速度的降低及晶粒的粗大化,还致使合金硬度也随之下降,由56.4(HV)降至51.3(HV)。

Influences of Cooling Rate on Microstructure and Mechanical Properties of Mg-5Al -0.5Y Alloy

The microstructure and hardness changes of cast Mg-5Al-0.5Y alloy in permanent mold, graphite mold and sand mould were comparatively investigated by optical microscopy(OM), scanning electron microscope(SEM), X-ray diffraction (XRD) and hardness tester at the cooling rates of 200 ℃/min、150 ℃/min and 60 ℃/min, and mechanism was analyzed. The results show that: with the decrease of the cooling rate, α-Mg grain sizes are coarsened, and the average size is increased from 52.83 μm to 68.96 μm, increased by 30.53%, while the β-Mg17Al12 phase exhibits continuous to discontinuous nets distributions, and its relative content is decreased from 10.35% to 8.67%, reduced by 16.23%. The hardness of Mg-5Al-0.5Y alloy is decreased from 56.4 HV to 51.3 HV as a result of the decrease of cooling rate and coarseness of grain sizes.