2060铝锂合金激光焊接组织及力学性能研究

发布时间：2019-01-09 15:20

【摘要】：铝锂合金是目前航空航天工业中最具应用潜力的新型轻质结构材料。激光焊接技术具有能量密度高、热输入小、焊接变形小以及加工柔性高等特点,可实现飞机制造中复杂结构的高精度三维拼接。然而,高强铝锂合金激光焊接头强韧性不足阻碍了其在航空、航天领域的应用。本文针对该难题,通过采用填充焊丝及稀土元素合金化等措施对高强铝锂合金激光焊接焊缝组织与性能进行调控,以期获得强韧性的最优匹配。论文以2060新型高强铝锂合金为对象,详细研究采用两种商用焊丝时焊缝的组织及性能,在此基础上添加稀土钪Sc,研究其对组织及性能的影响规律及作用机理。首先,研究了高强铝锂合金激光焊接接头局部微观组织的演变规律。通过考察填充4047 Al-Si焊丝接头不同区域的组织形态及析出相特征,并且利用显微硬度及小试样拉伸试验考察接头局部力学性能特点。结果表明,焊缝区强度较低,HAZ区内的局部强度随距熔合线距离增加而逐渐升高。靠近焊缝边缘的PMZ液化区形成共晶组织,使其硬度值最低。HAZ区的软化现象主要与强化相粒子数量明显减少有关。在温度较高的HAZ区域内原母材强化相完全溶解,随后析出少量的纳米级球状6’相(A13Li),而在较远处温度较低的HAZ区域,发生强化相聚合长大的过时效现象,使强度低于母材强度。其次,考察分别填充5087 Al-Mg及4047 Al-Si两种商用焊丝时焊缝组织及接头力学性能特点。结果表明,填充Al-Mg焊丝时,焊缝内形成大量的二十面体准晶相T2相(Al6Cu(Li,Mg)3),呈网状连续分布于晶界及枝晶间,使焊缝强度较低,接头抗拉强度为母材强度的63%。填充Al-Si焊丝时,焊缝内除θ相(Al2Cu)和少量的Mg2Si相外,大量不规则形的块状硬质相AlLiSi相形成,使焊缝强度较高,接头抗拉强度达到母材强度的70%以上然后,在填充Al-Mg及Al-Si焊丝的基础上分别继续添加sc,并对填充sc时采用两种焊丝的接头组织和性能进行对比分析。结果表明,添加sc均使接头组织和性能得到明显改善。焊缝组织显著细化,柱状晶消失,使得焊缝显微硬度显著增加,与母材硬度差异减小。当采用Al-Si焊丝焊接时,除了形成少量的含Sc第二相外,添加Sc后未改变焊缝内主要析出相种类。当采用Al-Mg焊丝焊接时,Sc的加入促进了θ相析出,但是由于仍有T,相存在,使其接头性能低于填充Al-Si焊丝时的接头性能。通过调整Sc的添加量,考察焊缝中Sc含量对焊缝组织及接头性能的影响规律。通过分析焊缝晶粒尺寸、析出第二相的种类及数量等,建立不同Sc含量时的焊缝组织细化效果以及Sc的存在形式与接头力学性能之间的变化关系。结果表明,填充两种焊丝的接头力学性能随焊缝中Sc含量的增加均有先增加后减小的趋势。只有当焊缝中形成初生Al3Sc相,才会对焊缝组织产生显著的细化作用而引起细晶强化。继续增加Sc的填充量,焊缝晶粒尺寸随Sc含量的变化减小,但是含Sc的第二相数量增加,接头的抗拉强度及延伸率明显下降。当焊缝中的Sc含量为0.72%时,填充4047 Al-Si焊丝的2060-T8铝锂合金激光焊接接头具有良好的综合力学性能,接头强韧性可以达到最优匹配,焊态下接头强度系数超过90%,延伸率由1.63%增加到3.63%。
[Abstract]:Al-Li alloy is the most promising new light structural material in the aerospace industry. The laser welding technology has the characteristics of high energy density, small heat input, small welding deformation and high processing flexibility, and can realize high-precision three-dimensional splicing of complex structures in the aircraft manufacturing. However, the strength and toughness of the high-strength aluminum-lithium alloy laser welding head hinder the application of the high-strength aluminum-lithium alloy laser welding head in the fields of aviation and space. In this paper, the structure and properties of high-strength Al-Li alloy laser welding are controlled by using the measures of filling welding wire and rare-earth element alloying, so as to obtain the optimal matching of the strong toughness. In this paper, using 2060 new high-strength aluminum-lithium alloy as the object, the microstructure and properties of the weld were studied in detail by using the two kinds of commercial welding wire. First, the evolution of the local microstructure of the high-strength Al-Li alloy laser welding joint is studied. The microstructure and precipitation phase characteristics of the different regions of the 4047Al-Si wire joint were investigated, and the local mechanical properties of the joint were investigated by means of the microhardness and the tensile test of the small sample. The results show that the strength of the weld zone is low, and the local strength in the HAZ increases with the distance from the fusion line. The PZ liquefaction zone near the weld edge forms a eutectic structure with the lowest hardness value. The softening phenomenon of the HAZ is mainly related to the decrease of the number of the reinforcing phase particles. In the HAZ region with higher temperature, the original mother material is completely dissolved, and then a small amount of nano-scale spherical 6 'phase (A13Li) is precipitated, while in the region of the HAZ at a lower temperature, the overaging phenomenon of strengthening phase polymerization and growth is carried out, so that the strength is lower than the strength of the mother material. Secondly, the mechanical properties of the joint and joint of 5087Al-Mg and 4047Al-Si were investigated. The results show that when the Al-Mg welding wire is filled, a large amount of icosahedral quasicrystal phase T2 (Al6Cu (Li, Mg) 3) is formed in the weld, and the mesh is continuously distributed between the grain boundary and the branch crystal, so that the strength of the weld is low, and the tensile strength of the joint is 63% of the strength of the parent material. When the Al-Si welding wire is filled, a large number of irregular-shaped massive hard-phase AlLiSi phases are formed in the welding line in addition to the Al-Si phase (Al2Cu) and a small amount of the Mg2Si phase, so that the strength of the welding line is high, the tensile strength of the joint reaches more than 70% of the strength of the mother material, and the sc is continuously added on the basis of filling the Al-Mg and Al-Si welding wires, and the joint structure and the performance of the two welding wires are compared and analyzed in the filling sc. The results show that the addition of sc improves the tissue and performance of the joint. The microstructure of the welding seam is obviously refined, and the crystal grain is disappeared, so that the micro-hardness of the welding line is obviously increased, and the difference of the hardness of the mother material is reduced. When the Al-Si welding wire is used for welding, in addition to forming a small amount of the Sc-containing second phase, the main precipitated phase in the weld is not changed after the addition of Sc. When the Al-Mg welding wire is used for welding, the addition of Sc promotes the precipitation of the alloy phase, but due to the fact that T is still present, the joint performance is lower than that of the joint when the Al-Si welding wire is filled. By adjusting the addition of Sc, the influence of the content of Sc in the weld on the structure of the weld and the performance of the joint was investigated. By analyzing the grain size of the weld, the type and quantity of the second phase, the effect of the microstructure refinement of the weld and the relationship between the existence of Sc and the mechanical properties of the joint are established. The results show that the mechanical properties of the joint filled with the two kinds of welding wire have a tendency to decrease with the increase of the content of Sc in the weld. The formation of the primary Al3Sc phase in the weld results in a significant refinement of the weld tissue, resulting in a fine-grained reinforcement. The filling amount of Sc is increased, the grain size of the weld decreases with the change of Sc content, but the second phase quantity of Sc is increased, and the tensile strength and the elongation of the joint are obviously reduced. When the content of Sc in the welding seam is 0.72%, the 2060-T8 Al-Li alloy laser welding joint filled with 4047Al-Si welding wire has good comprehensive mechanical property, and the strength coefficient of the joint is more than 90% under the welding state, and the elongation is increased from 1.63% to 3.63%.
【学位授予单位】：北京工业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG456.7

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