轧制及热处理工艺对6xxx系列铝合金组织与性能影响的研究

【作者】 李毅；

【导师】 周晓龙； 张鹏举；

【作者基本信息】 昆明理工大学 ， 材料与化工（专业学位）， 2024， 硕士

【摘要】 6xxx系合金以其良好的塑性、较低的密度、较高的耐蚀性、良好的导电性和可热处理强化等特点而被广泛应用于交通运输、航空航天、电力电器等领域。但目前6xxx系铝合金应用中存在强度较低等问题制约了合金的应用范围。目前关于提升6xxx系铝合金强度的方法有很多主要包括添加合金元素和合理优化加工工艺等,通过添加大量合金元素的方法虽然能够有效提高合金强度但同时也会损害合金的塑性、导电性和成型性等特点,降低合金的应用范围。关于6xxx系铝合金板材在制备和加工过程中微观组织结构和性能变化仍缺乏系统性的研究。本文以冷轧的方式制备6xxx系铝合金板材,通过改变均匀化处理和固溶过程的重要参数,研究了板材在加工制备过程中组织结构的演变与合金性能之间的对应关系。研究了不同冷轧压下率合金的组织结构和演变规律及其对性能的影响。在铸态合金中可观察到的第二相种类主要有α-Al Fe Si、β-Al Fe Si、π-Al Fe Mg Si以及β相粒子,轧制过程中铁硅相粒子遭到破碎尺寸明显降低。轧制过程中对基体的净化作用较高使合金电导率随压下率增加而增加,同时轧制过程,降低了晶粒尺寸,合金硬度明显提高。多次轧制后,晶粒呈纤维状,平均晶粒尺寸降低了约70%,合金中织构以copper取向、S取向、Brass取向为主,Cube取向和Goss取向的织构占比较低。研究了均匀化时长对合金显微组织与性能的影响。在均匀化处理过程中Mn元素与铁硅相粒子相互作用形成α-Al Fe Mn Si相粒子。由于Mn元素从基体析出降低了晶体点阵畸变程度合金电导率得到大幅提高,同时均匀化处理使轧制后的合金晶粒粗化,位错密度降低,导致合金硬度大幅降低。研究了固溶处理时长对轧制后合金显微组织的转变以及对性能的影响。采用的固溶处理温度为560℃,在固溶过程中α-Al Fe Mn Si相粒子保持相对稳定,而β相粒子的溶解程度随固溶时间的增加而加剧。在保温10min后,仅能发现少数尺寸较大的β相粒子,30分钟后,β相粒子几乎全部溶解。随着溶质原子的回溶,合金电导率显著降低。固溶处理过程促进了变形晶粒的再结晶行为。固溶处理5min时合金的再结晶程度最高,平均晶粒尺寸最小;随着固溶时间的增加,晶粒略微长大,Cube织构和Goss织构的含量增加。合金中的几何必须位错密度也随固溶时间的增加而逐渐降低,合金硬度的变化趋势与之相同。研究了时效后合金的组织结构及合金力学性能。对不同固溶时长处理后的合金进行180℃×30min时效处理,时效后能够发现细小的β″相和β′相粒子。通过对时效后合金进行DSC分析发现,固溶时间越长,β相粒子回溶程度越高,越有利于在时效过程获得β″相粒子。时效处理导致合金基体中固溶原子的析出,从而减少了铝基体的固溶度著提升了合金的电导率。通过拉伸测试发现,当固溶时间较短时,时效后的合金表现出较低的延伸率。随着固溶时长增加,合金的抗拉强度呈现出先增加后降低的变化趋势,而合金的延伸率和应变硬化率则随着固溶时长的增加而逐渐提高。在固溶5min+时效处理后,合金的抗拉强度达到最大,但此时延伸率较低;而经过固溶处理10分钟加时效处理后,合金的抗拉强度略微下降,但延伸率显著提高,综合性能优异。更多还原

【Abstract】 6xxx series alloys are widely used in transportation,aerospace,power appliances and other fields due to their good plasticity,low density,high corrosion resistance,good electrical conductivity and heat treatment strengthening.However,there are some problems such as low strength in the application of 6xxx series aluminum alloy,which restrict the application range of the alloy.At present,there are many methods to improve the strength of 6xxx series aluminum alloys,including adding alloying elements and reasonably optimizing the processing technology.Although adding a large number of alloying elements can effectively improve the strength of the alloy,it will also damage the plasticity,conductivity,and formability of the alloy,and reduce the application range of the alloy.In terms of processing technology,there is still a lack of systematic research on the changes of microstructure and properties of 6xxx series aluminum alloys during preparation and processing.In this thesis,6xxx series aluminum alloy sheets were prepared by cold rolling.By changing the important parameters of homogenization treatment and solid solution process,the relationship between the evolution of microstructure and the properties of the alloy during the processing and preparation of the sheets was studied.The microstructure and evolution of alloys with different cold rolling reduction rates and their effects on properties were studied.In the as-cast alloy,α-Al Fe Si,β-Alfesi,π-Al Fe Mg Si andβ phase particles are mainly observed,and the crushing size of iron-silicon phase particles is significantly reduced during rolling.During the rolling process,the higher cleaning effect on the matrix makes the alloy conductivity increase with the increase of the reduction rate,and the grain size is reduced and the hardness of the alloy is obviously increased.After repeated rolling,the grain is fibrous and the average grain size is reduced by about 70%.The texture of the alloy is dominated by copper orientation,S orientation and Brass orientation,and the texture of Cube orientation and Goss orientation is relatively low.The effect of homogenization time on the microstructure and properties of the alloy was studied.During the homogenization treatment,the Mn element interacts with the iron-silicon phase particles to form α-Al Fe Mn Si phase particles.Due to the precipitation of Mn element from the matrix,the degree of crystal lattice distortion is reduced,and the conductivity of the alloy is greatly improved.At the same time,the homogenization treatment coarsens the grains of the alloy after rolling,reduces the dislocation density,and leads to a significant reduction in the hardness of the alloy.The effect of solution treatment time on the microstructure transformation and properties of the alloy after rolling was studied.The solution treatment temperature is 560 °C.The α-Al Fe Mn Si phase particles remain relatively stable during the solution treatment process,while the dissolution degree of β phase particles increases with the increase of solution time.After holding for 10 min,only a small number of larger β phase particles can be found.After 30 min,the β phase particles are almost completely dissolved.With the re-dissolution of solute atoms,the electrical conductivity of the alloy decreases significantly.The solution treatment process promotes the recrystallization behavior of deformed grains.When the solution treatment is 5min,the recrystallization degree of the alloy is the highest and the average grain size is the smallest.With the increase of solution time,the grains grow slightly,and the content of Cube texture and Goss texture increases.The geometrically necessary dislocation density in the alloy also gradually decreases with the increase of solution time,and the change trend of the hardness of the alloy is the same.The microstructure and mechanical properties of the alloy after aging were studied.The alloys treated with different solid solution time were aged at 180 °C × 30 min,and fine β " phase and β ’ phase particles were found after aging.Through the DSC analysis of the alloy after aging,it is found that the longer the solid solution time,the higher the degree of dissolution of the βphase particles,and the more favorable the β″phase particles are obtained during the aging process.Aging treatment leads to the precipitation of solid solution atoms in the alloy matrix,which reduces the solid solubility of the aluminum matrix and significantly improves the electrical conductivity of the alloy.Through the tensile test,it was found that when the solution time was short,the alloy after aging showed a lower elongation.With the increase of solid solution time,the tensile strength of the alloy increases first and then decreases,while the elongation and strain hardening rate of the alloy increase gradually with the increase of solid solution time.After solution treatment for 5min + aging treatment,the tensile strength of the alloy reaches the maximum,but the elongation is low.After solution treatment for 10 minutes and aging treatment,the tensile strength of the alloy decreases slightly,but the elongation increases significantly,and the comprehensive performance is excellent.更多还原