不同Ce含量2519A铝合金高应变速率下的力学性能和显微组织

【作者】 刘军；

【导师】 张新明；

【作者基本信息】 中南大学 ， 材料加工工程， 2012， 硕士

【摘要】 2519A铝合金作为新一代装甲材料,提高其抗冲击性能是研究的关键。本文利用分离式Hopkinson压杆装置对不同Ce含量(0,0.2%,0.4%)的2519A铝合金进行动态压缩实验,压缩温度为293K和573K,名义应变速率为1200s-1、3100s-1、5100s-1,得到合金在不同条件下的应力-应变曲线,并分别对不同合金的吸能能力和绝热温升进行分析和计算；利用维氏硬度仪、金相显微镜、X射线衍射仪、扫描电镜、透射电镜等对冲击后的试样进行硬度测试和显微组织观察,得到以下结论：(1)建立了合金冲击后硬度与应变速率的关系。随着应变速率的升高,冲击后试样的硬度值先略微升高,然后下降；相同状态下添加0.2%Ce合金的硬度值明显高于未添加的和添加0.4%Ce试样的硬度。当温度为573K时,由于热软化作用明显,合金的硬度小于293K下的。(2)得到了不同Ce含量的合金在不同条件下的动态力学性能规律。对不同成分不同压缩条件下合金的应力-应变曲线进行分析,相同应变速率和温度下,添加0.2%Ce合金的动态屈服强度最高,吸能能力最好,因此其抗冲击性能最好；添加0.4%Ce时,合金的动态屈服强度和吸能能力反而下降。当应变速率为3100s1,温度为293K时,含0.2%Ce合金的动态屈服强度达到614MPa,明显高于未添加(550MPa)和添加0.4%Ce (545MPa)的合金。(3)探明了Ce对2519A强化相析出规律的影响。当应变速率为1200s-1和3100s-1时,添加0.2%Ce合金0’相的面积分数最大,分布更细小弥散；而当应变速率达到5100s-1时,293K下,θ’相明显粗化长大,并且向θ相转化,但是添加0.2%Ce合金的转化最慢；573K下,强化相出现回溶现象。(4)研究了Ce在冲击后合金中的存在形式,并探究Ce在合金中的作用机理。Ce主要和Al、Cu元素形成稀土化合物,这种化合物熔点较高,能够提高合金的耐热性能；而且在晶界晶内都有分布,能够提高晶界的高温性能。从团簇、动力学、热力学等方面讨论了Ce可能的作用机理。更多还原

【Abstract】 As a new generation of armored material, the key problem of aluminum alloy2519A is to improve the impact property. Aluminum alloy2519A with different contents of Ce (0,0.2%,0.4%) was dynamically impacted by split Hopkinson pressure bar (SHPB) at different temperatures of293K and573K and nominal strain rates of1200s-1,3100s-1and5100s-1. Corresponding true stress-strain curve of each condition was obtained. And the kinetic energy-absorbing capacity and the adiabatic temperature were calculated and analyzed. The hardness of the impacted specimens was tested by Vickers hardness-testing device. The microstructure was investigated by optical microscopy (OM), scanning electron microcopy(SEM), X-ray diffractometer (XRD) and transmission electron microscopy(TEM). Main conclusions are listed in the following:(1)The relationship between strain rates and hardness was established. With increasing strain rate, the hardness of the impacted specimens increased slightly and then decreased. The hardness of alloy with0.2%Ce was higher than that of the alloys with0%Ce and0.4%Ce. Besides, the hardness of specimens impacted at temperature of573K was lower than the counterpart at293K, mainly due to the effect of hot softening.(2)The law of dynamic mechanical property with different alloys at different conditions was obtained. After the analysis of different true stress-strain curves, the0.2%Ce alloy had the highest dynamic yield strength and the highest energy absorption ability compared with others at the same strain rate and temperature, so the dynamic mechanical property of0.2%Ce alloy was the highest. However, the property of the alloy decreased when the addition of Ce reached0.4%. the dynamic yield strength of0.2%Ce alloy reached614MPa, which was obviously higher than that of alloys with0%Ce (550MPa) and0.4%Ce (545MPa).(3)The influence of Ce on the precipitated phases of aluminum alloy2519A was investigated. In case of strain rate of1200s-1and3100s-1, precipitated phases in0.2%Ce alloy were distributed more dispersedly and homogeneously than others, and had the highest area fraction. As the strain rate increased to5100s-1,θ’phase began to coarsen and transform to0at293K while0’phase changed most slowest in0.2%Ce alloy. However, at573K, a re-dissolution phenomenon of hardening phases took place.(4)The existence form of Ce in aluminum alloy2519A was studied and the mechanism of action was explored. Ce mainly exists in the form of rare earth compound with Al and Cu. This type of compound has a relatively high melting point and is distributed both inside grains and along grain boundaries, which corresponding to improvements in the strength of grain boundaries and thermal resistance of the alloy. The action mechanism of Ce was explored in terms of cluster theory, thermodynamic kinetic.更多还原