摘要
2060-T8E30作为理想的下机翼材料,在飞行过程中主要承受拉伸载荷。本研究采用光学显微镜(OM)、扫描电镜(SEM)、透射电镜(TEM)以及室温拉伸和扫描电镜的原位拉伸对2060-T8E30铝锂合金薄板的微观组织、平面各向异性和原位拉伸断裂试验过程中的微观组织演变过程进行了系统研究。研究结果表明,2060-T8E30铝锂合金薄板在与轧制方向成0°方向材料的屈服强度和抗拉强度比45°和90°方向高,延伸率则是90°方向最高,抗拉强度的平面各向异性指数为3.8%。等轴再结晶晶粒组织和Goss{110}<001>可能是导致其抗拉强度和屈服强度各向异性指数相对较低的主要原因。微观组织研究结果表明,2060-T8E30合金的主要强化相是T1相,同时含有少量S’相,晶界未观察到无沉淀析出带。在原位拉伸过程中,当拉伸变形量较小时晶界第二相粒子发生破碎形成细小裂纹源沿晶界位置首先开裂,随着变形量的增加,共格β’相和小尺寸的T1相易被切过,晶内出现大量滑移带,最终2060-T8E30铝锂合金薄板以穿晶和沿晶相结合的方式断裂。
The development of aluminum-lithium alloy had a history of more than 80 years.The 2060 aluminum alloy,the 3 rd generation Al-Li alloy,was registered in the Aluminum Association in 2011.Its low density,high strength,high elastic modulus,fatigue crack growth resistance,and excellent corrosion resistance were increasingly replacing traditional 2 xxx and 7 xxx aluminum alloys in aerospace applications.It had become one of the key materials for achieving a reduction in fuel consumption.Especially as an ideal lower wing material,it could replace the traditional 2 X24 alloy.The lower wing was mainly subjected to tensile loads during flight.Optical microscope(OM),scanning electron microscope(SEM),and transmission electron microscope(TEM)were used to characterize the recrystallized grain structure and the precipitates of 2060-T8 E30 aluminum-lithium sheet.Tensile samples were taken in the L(longitudinal)direction(0°to the rolling direction),45°to the rolling direction,and LT(long transverse)90°to the rolling direction.Tensile properties were evaluated using standard ambient temperature tensile tests according to GB/T 228.1,and the in-plane anisotropy index(IPA)was calculated to understand the anisotropy of the 2060-T8 E30 Al-Li alloy sheet.The non-notched samples were used for the in-situ tensile test of the scanning electron microscope.The samples were polished mechanically and etched in a solution of 1.0%HF,1.5%HCL,2.5%HNO3,and 95%H2 O(volume fraction)before the in-situ tests to investigate the microstructure evolution in the tensile process of the 2060-T8 E30 Al-Li alloy.The results showed that the 2060-T8 E30 alloy presents pancake shape grains elongated to the rolling direction with a high recrystallization fraction.The average grain size was 340μm in L-ST plane,325μm in LST plane,and 42μm LT-ST plane,respectively.Only the T1 precipitate(Al2 CuLi)diffraction pattern was observed in[112],[110],and[001]zone axis,but noδ’phase(Al3 Li)diffraction pattern was found.The precipitation microstructure of the 2060-T8 E30 alloy was dominated by the presence of the T1 precipitate,along with a small number of S’platelets.Besides,no precipitated free zone(PFZ)was observed at the grain boundary.The results showed that the yield strength and ultimate strength of the 2060-T8 E30 aluminum-lithium sheet in the 0°direction with the rolling direction were higher than those in the 45°and 90°orientations.The elongation was the highest in the 90°orientation.The tensile strength IPA was only 3.7%,while the yield strength IPA was 8.2%.Compared to the 2198-T8 alloy’s mechanical properties,the yield strength and ultimate strength in-plain anisotropy of 2060-T8 E30 alloy were much smaller than that of 2198-T8 alloy specimen,while the IPA of elongation was smaller than that of 2060 alloy.The further calculation reveals that 45°orientationηmax-1 was greater than 90°orientationηmax-1 in 2060-T8 E30 alloy dominated by Goss{110}<001>texture,indicating that the 45°orientation yield strength of the sheet was greater than 90°orientation.Moreover,the IPA of the Schmidt factor of Goss{110}<001>and Cube{100}<001>in the 0°,45°and 90°orientations was lower than that of other types of textures.Compared to the aluminum-lithium alloy with other textures,the 2060-T8 E30 sheet had a lower IPA.It was postulated here that the equiaxed recrystallized grain structure and Goss{110}<001>texture might be contributed to the relatively low in-plane anisotropy of tensile strength and yield strength.The fracture morphology characteristics of the 2060-T8 E30 alloy tensile specimens were mainly dimples and a small number of secondary cracks formed by intergranular cracking.The high magnification fracture showed the plane formed by intergranular propagation and small-sized equiaxed dimples,indicating that the 2060-T8 E30 alloy was dominated by transgranular fracture.The following conclusions could be drawn from the in-situ SEM study of tensile crack initiation and propagation behavior in the 2060-T8 E30 sheet.At initial loading,slip bands are not observed in the grain,the coarse second phase particles at the grain boundaries were broken to form micro-cracks,and then the crack propagated along the grain boundaries.As the load increased,on the one hand,the coherentβ’precipitate was easy to be cut.On the other hand,although it was difficult for dislocations to cut through the incoherent S’precipitate,the volume fraction of S’precipitate in the 2060-T8 E30 alloy was relatively small,weaken the dislocation barrier.Finally,a large number of slip bands were observed inside the grains.Slip accumulation at the grain boundary caused more grain boundary cracks.As the amount of stretching increased,the number and depth of slip bands continued to increase,and the width and length of grain boundary crack also increased.The slip bands were distorted,and the grains were slightly deflected.Since there was no PFZ in the 2060-T8 E30 sheet,the types and densities of the precipitation both inside the grains and grain boundaries were equivalent,resulting in the strength inside the grain and on the grain boundary was basically identical.Eventually,the sample broke through with the combination of transgranular and intergranular modes.
作者
郝敏
王亮
陈军洲
雷越
李国爱
Hao Min;Wang Liang;Chen Junzhou;Lei Yue;Li Guoai(Beijing Engineering Research Center of Advanced Aluminum Alloys and Application,Beijing Institute of Aeronauti-cal Materials,Beijing 100095,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2021年第6期641-649,共9页
Chinese Journal of Rare Metals
基金
国家自然科学基金项目(51474195)资助。
关键词
铝锂合金
原位拉伸
平面各向异性
变形机制
Al-Li alloy
in-situ SEM tension test
in-plane anisotropy
deformation mechanism
作者简介
郝敏(1985-),女,陕西兴平人,硕士,工程师,研究方向:变形铝合金、航空材料,E-mail:haomin222@163.com;通信作者:李国爱,高级工程师,电话:010-62497416,E-mail:liguoai_1@163.com。
