2060鋁鋰合金激光焊接組織及力學性能研究
發(fā)布時間：2019-01-09 15:20
【摘要】：鋁鋰合金是目前航空航天工業(yè)中最具應用潛力的新型輕質結構材料。激光焊接技術具有能量密度高、熱輸入小、焊接變形小以及加工柔性高等特點,可實現飛機制造中復雜結構的高精度三維拼接。然而,高強鋁鋰合金激光焊接頭強韌性不足阻礙了其在航空、航天領域的應用。本文針對該難題,通過采用填充焊絲及稀土元素合金化等措施對高強鋁鋰合金激光焊接焊縫組織與性能進行調控,以期獲得強韌性的最優(yōu)匹配。論文以2060新型高強鋁鋰合金為對象,詳細研究采用兩種商用焊絲時焊縫的組織及性能,在此基礎上添加稀土鈧Sc,研究其對組織及性能的影響規(guī)律及作用機理。首先,研究了高強鋁鋰合金激光焊接接頭局部微觀組織的演變規(guī)律。通過考察填充4047 Al-Si焊絲接頭不同區(qū)域的組織形態(tài)及析出相特征,并且利用顯微硬度及小試樣拉伸試驗考察接頭局部力學性能特點。結果表明,焊縫區(qū)強度較低,HAZ區(qū)內的局部強度隨距熔合線距離增加而逐漸升高�？拷缚p邊緣的PMZ液化區(qū)形成共晶組織,使其硬度值最低。HAZ區(qū)的軟化現象主要與強化相粒子數量明顯減少有關。在溫度較高的HAZ區(qū)域內原母材強化相完全溶解,隨后析出少量的納米級球狀6’相(A13Li),而在較遠處溫度較低的HAZ區(qū)域,發(fā)生強化相聚合長大的過時效現象,使強度低于母材強度。其次,考察分別填充5087 Al-Mg及4047 Al-Si兩種商用焊絲時焊縫組織及接頭力學性能特點。結果表明,填充Al-Mg焊絲時,焊縫內形成大量的二十面體準晶相T2相(Al6Cu(Li,Mg)3),呈網狀連續(xù)分布于晶界及枝晶間,使焊縫強度較低,接頭抗拉強度為母材強度的63%。填充Al-Si焊絲時,焊縫內除θ相(Al2Cu)和少量的Mg2Si相外,大量不規(guī)則形的塊狀硬質相AlLiSi相形成,使焊縫強度較高,接頭抗拉強度達到母材強度的70%以上然后,在填充Al-Mg及Al-Si焊絲的基礎上分別繼續(xù)添加sc,并對填充sc時采用兩種焊絲的接頭組織和性能進行對比分析。結果表明,添加sc均使接頭組織和性能得到明顯改善。焊縫組織顯著細化,柱狀晶消失,使得焊縫顯微硬度顯著增加,與母材硬度差異減小。當采用Al-Si焊絲焊接時,除了形成少量的含Sc第二相外,添加Sc后未改變焊縫內主要析出相種類。當采用Al-Mg焊絲焊接時,Sc的加入促進了θ相析出,但是由于仍有T,相存在,使其接頭性能低于填充Al-Si焊絲時的接頭性能。通過調整Sc的添加量,考察焊縫中Sc含量對焊縫組織及接頭性能的影響規(guī)律。通過分析焊縫晶粒尺寸、析出第二相的種類及數量等,建立不同Sc含量時的焊縫組織細化效果以及Sc的存在形式與接頭力學性能之間的變化關系。結果表明,填充兩種焊絲的接頭力學性能隨焊縫中Sc含量的增加均有先增加后減小的趨勢。只有當焊縫中形成初生Al3Sc相,才會對焊縫組織產生顯著的細化作用而引起細晶強化。繼續(xù)增加Sc的填充量,焊縫晶粒尺寸隨Sc含量的變化減小,但是含Sc的第二相數量增加,接頭的抗拉強度及延伸率明顯下降。當焊縫中的Sc含量為0.72%時,填充4047 Al-Si焊絲的2060-T8鋁鋰合金激光焊接接頭具有良好的綜合力學性能,接頭強韌性可以達到最優(yōu)匹配,焊態(tài)下接頭強度系數超過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%.
【學位授予單位】：北京工業(yè)大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG456.7
本文編號：2405799
[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%.
【學位授予單位】：北京工業(yè)大學
【學位級別】：博士
【學位授予年份】：2016
【分類號】：TG456.7
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