高强度铸造Al-Cu-Mn合金的θ相偏析和室温性能研究

发布时间：2018-08-29 14:10

【摘要】：ZL205A合金是由北京航空材料研究院于20世纪70年代研制成功的高强韧铸造铝合金,具有比强度高、耐腐蚀性和机械加工性能优良等特点,应用于航空航天、兵器、冶金等领域,但结晶温度区间较宽,在铸造过程中易产生缩松、偏析等铸造缺陷,并有晶间腐蚀和应力腐蚀倾向,限制了在高性能机械零件和民用工业中的广泛应用。本文旨在拓宽高强度铸造铝合金在复杂薄壁铸件和精密成形领域的产业化应用,分别从铸造工艺参数、微合金化和热处理三个方面,研究了它们对ZL205A合金的微观组织和性能的影响,并对作用机理做了详尽和深入的分析,为进一步控制材料的凝固行为和完善微观组织精确调控理论奠定了基础。浇注温度和温度梯度是控制材料凝固行为的关键工艺参数。通过改变浇注温度(680℃~740℃),研究了不同壁厚(5 mm~25 mm)的铸件在T6热处理前后微观组织和性能的变化。结果表明,随着浇注温度的升高,ZL205A铸态合金中的θ相更倾向于以颗粒状和细长条状存在,且总体残余量减少,分布也变得相对均匀规则,对基体的割裂减少。由壁厚引起的温度梯度对θ相形貌和径向成分梯度产生一定影响,残余θ相中的Cu原子浓度随壁厚增加而逐渐降低,降低温度梯度能促进Cu原子在基体中的固溶度,从而增强固溶强化效果。经过T6热处理后,晶体内的残余组织大幅度减少,合金元素在固溶处理和时效过程中基本上全都溶入基体,成分偏析降低,同时合金的组织致密度明显高于铸态。不同的微合金化元素与铝合金的作用机理不同,形成的金属间化合物与基体组织存在较大的差异,会对合金中二次相的析出过程产生重要影响,这将严重影响合金在固溶处理后的综合力学性能。为此,本文比较并分析了在ZL205A合金中单独添加微量Er和复合添加Er、Zr元素后θ相的偏析行为,并对材料铸造性能、力学性能和断裂性能的影响机理进行研究。研究表明,单独添加Er和复合添加Er、Zr元素均能显著提高合金液的流动性,并减少缩松、缩孔、夹砂等铸造缺陷的生成,有效地改善了ZL205A合金的铸造性能。单独添加Er元素会对Cu原子的扩散和固溶过程产生较大影响,导致θ共晶相沿晶界发生偏聚,且随着添加量的增加(0.1%~0.5%),晶体内的残余共晶组织增多。Er具有较高的化学活性,在凝固过程中容易吸附在原子团和晶胚的界面上,降低θ,相的界面能和形核激活能,使TTT曲线左移,从而加速了固溶处理和时效过程中GP区和θ,相的脱溶进度,并促使析出少量的θ平衡相。微量Er、Zr元素可以细化晶粒,使θ相分枝现象加重,且造成一定程度的偏析团聚,最后导致晶界组织的宽度减小,甚至在有些地方熔断为颗粒状,而在交汇晶界处扩展为片状存在。T5处理能够促使合金组织和成分均匀化,同时使溶质原子充分扩散,从而阻碍了变形过程中位错的运动和亚晶界的迁移。
[Abstract]:ZL205A alloy is a kind of high strength and toughness cast aluminum alloy developed by Beijing Aeronautical Materials Research Institute in the 1970s. It has the characteristics of high specific strength, high corrosion resistance and excellent machining properties. It is used in aerospace, weapons, metallurgy and other fields. However, the wide range of crystallization temperature is easy to produce casting defects such as shrinkage, segregation and intergranular corrosion and stress corrosion, which limits its wide application in high performance mechanical parts and civil industry. The purpose of this paper is to expand the industrial application of high strength cast aluminum alloy in complex thin-walled castings and precision forming fields, respectively from three aspects: casting process parameters, microalloying and heat treatment. Their effects on microstructure and properties of ZL205A alloys were studied, and the mechanism of action was analyzed in detail, which laid a foundation for further controlling solidification behavior of materials and perfecting the theory of precise control of microstructure. Pouring temperature and temperature gradient are the key process parameters to control solidification behavior. The changes of microstructure and properties of castings with different wall thickness (5 mm~25 mm) before and after T6 heat treatment were studied by changing the pouring temperature (680 鈩，

本文编号：2211440