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2219属于Al-Cu系析出强化型铝合金,具有良好的断裂韧性和优异的低温性能,在焊接过程中具有较低的裂纹敏感性,被广泛应用于航空航天领域主体承载结构,而焊接加工质量往往直接决定构件的使用寿命和服役安全.
常用于2219铝合金的熔化焊方法包括激光焊[1-3]、电子束焊[4]和钨极惰性气体保护焊[5-7],其中激光焊能量集中、热输入小和生产效率高,在生产制造中展现出很好的应用前景. 在熔化焊的热作用下,接头微观组织的弱化常常引起力学性能的恶化,加之激光焊技术更易产生气孔缺陷. 为了防止铝合金焊接缺陷并改善接头性能,激光摆动焊接工艺可以扩大间隙适应性、抑制气孔和凝固裂纹产生和改变晶粒生长行为[8-11]. Wang等人[9]采用激光线性、圆形和无穷摆动工艺对5A06铝合金焊接进行了研究,结果表明,与非摆动焊接相比,摆动工艺会降低焊缝的深宽比,在降低接头气孔率的同时提高抗拉强度. Wang等人[12]对比研究了激光无摆动、横向摆动、纵向摆动和圆形摆动对6061焊缝晶粒形成的影响机制,结果表明,激光摆动焊接通过搅拌作用改善了焊缝形貌、促进熔化区内等轴晶的形成,其中圆形摆动焊缝内等轴晶数量最多,但不同摆动工艺对接头抗拉强度没有显著影响. Wu等人[13]对1060铝合金激光摆动焊接进行了研究,结果表明,摆动焊接可以改变激光束在匙孔中的作用位置和匙孔开口尺寸使匙孔不易塌陷和闭合,有利于降低匙孔型气孔的大小和数量. 然而,目前关于2219铝合金激光摆动焊接接头微观组织和力学性能的研究报道较少.
在不同摆动频率和幅度下开展了2219-T651铝合金激光摆动焊接试验,分析了摆动工艺参数对焊缝气孔率、宏观成形、微观组织和力学性能的影响规律,该研究旨在推动摆动激光焊接技术在航空航天领域铝合金承载结构中的应用.
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试验选用尺寸为100 mm × 50 mm × 6 mm的2219-T651铝合金试板,其化学成分如表1所示. 2219-T651铝合金的抗拉强度为458 MPa. 试验前用砂纸打磨去除表面氧化层,随后用乙醇擦洗清理表面.
表 1 2219-T651铝合金化学成分(质量分数,%)
Table 1. Chemical compositions of 2219-T651 Al alloy
Cu Mn Fe Ti Zn Si Al 6.62 0.27 0.11 0.04 0.04 0.04 余量 使用IPGYLS−4000型光纤激光器并通过Precitec型摆动头进行激光摆动焊接,为防止氧化,采用纯度为99.99%的氩气进行三路(主吹、正面和背面)气体保护. 激光离焦量为 + 3 mm并垂直作用于试板表面,激光功率为4 kW,焊接速度为3 m/min,光束垂直于焊接方向横向摆动,摆动频率为0 ~ 400 Hz,摆动幅度为0 ~ 2.5 mm. 焊接完成后清理试样表面,使用MG325 型X射线探伤机进行气孔探测,随后使用Image-Pro Plus 6.0软件对气孔尺寸和数量进行统计,基于气孔在焊缝中的面积占比计算得到焊缝气孔率.
用线切割切取金相试样,打磨抛光后用Keller试剂(2.5 mL HNO3 + 1.5 mL HCl + 1.0 mL HF + 95 mL H2O)进行腐蚀,用Nikon ECLIPSE MA200型倒置光学显微镜和HITACHI SU6600型扫描电子显微镜观察宏观和微观组织,用X射线能谱仪进行元素分析. 使用HXD-1000型显微维氏硬度计对接头进行硬度测定,测试线距试样上表面1 mm,压痕间隔0.2 mm,加载载荷0.49 N,保载时间10 s. 垂直焊接方向切取拉伸试样,尺寸如图1所示,试样厚度为2 mm,使用INSTRON 5982型万能材料试验机进行拉伸试验,拉伸速率为1 mm/min.
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表2和图2为不同摆动频率和幅度下接头的宏观成形情况和X光气孔检测结果. 当摆动幅度为1.5 mm、摆动频率从0 Hz升高至50 Hz时,熔宽变化不大;当摆动频率继续增大后,熔宽显著增大,随后几乎不变,而熔深随摆动频率的升高逐渐减小. 当摆动频率为150 Hz时,熔宽随摆动幅度的增大逐渐增大;当摆动幅度从0 mm增大至0.5 mm时,熔深变化不大,继续增大摆动幅度,熔深显著减小.
表 2 不同摆动频率和幅度下接头宏观成形
Table 2. Formation of joints under different oscillating frequency and amplitude
摆动频率
f/Hz摆动幅度
A/mm熔宽
w/mm熔深
h/mm气孔率
P(%)0 0 3.9 3.6 8.81 50 1.5 4.0 3.4 7.14 150 1.5 4.5 3.2 5.56 400 1.5 4.4 3.1 7.29 150 0.5 4.1 3.7 7.66 150 2.5 4.7 2.7 1.66 图 2 焊缝的宏观形貌和X光气孔检测结果
Figure 2. Macroscopic morphology and X-ray porosity test results of the welds. (a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude1.5 mm; (c) oscillating frequency 150 Hz, oscillating amplitude1.5 mm; (d) oscillating frequency 400 Hz, oscillating amplitude1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
图3为不同摆动频率和幅度下焊缝的气孔率. 无摆动焊接时焊缝气孔率为8.81%,摆动焊接时焊缝的气孔率低于无摆动焊接时焊缝的气孔率. 当摆动幅度为1.5 mm时,随着摆动频率的提高,气孔率先降低至5.56%(摆动频率150 Hz),之后逐渐升高至7.29%(摆动频率400 Hz). 高频横向摆动时,匙孔更细且形状更不规则,这可能会导致匙孔更不稳定,生成更多气泡[14]. 当摆动频率为150 Hz时,随着摆动幅度的提高,气孔率不断下降,当摆动幅度为2.5 mm时,气孔率降低至1.66%. 随着摆动幅度的增大,激光能量作用区域增加峰值降低,匙孔稳定性提升;同时较宽的摆动幅度下熔池更宽更浅,有助于气泡的逃逸[15-16]. 此外,由图3对比可知,与摆动频率相比,摆动幅度的增加显著抑制了焊缝气孔.
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图4为无摆动焊接接头的微观组织. 接头可大致分为熔化区(fusion zone, FZ)、热影响区(heat affected zone, HAZ)和母材(base metal, BM). 与热影响区相比,熔化区主要由尺寸细小的等轴晶组成. 表3为无摆动焊接接头能谱分析结果,可以看出,熔化区深色区域为α(Al)基体,白色部分为α(Al) + θ(Al2Cu)共晶相,主要分布在枝晶间和晶界. 相比于热影响区和母材,由于熔化区含Cu共晶相大量出现,因此熔化区α(Al)基体中Cu元素含量较少.
图 4 无摆动焊接接头的微观组织
Figure 4. Microstructure of the non-oscillating welded joint. (a) integral joint; (b) weld center; (c) HAZ; (d) BM
表 3 无摆动焊接接头的能谱分析结果(质量分数,%)
Table 3. EDS results of the non-oscillating welded joint
位置 Al Cu 可能相 1 98.14 1.86 α 2 78.45 21.55 α + θ 3 93.09 6.91 α 4 78.17 21.83 α + θ 5 94.42 5.58 α 6 77.64 22.36 α + θ 7 58.66 41.34 θ 图5为不同摆动频率和幅度下焊缝中心的微观组织. 当摆动频率为150 Hz、摆动幅度为0.5 mm时,焊缝中心晶粒尺寸和无摆动时相差不大. 当摆动幅度为1.5 mm时,随着摆动频率的提高,晶粒尺寸有所细化. 当摆动频率为150 Hz时,随着摆动幅度提高到1.5 mm和2.5 mm时,在晶粒尺寸细化方面表现出相同的现象.
图 5 不同摆动频率和幅度下焊缝中心微观组织
Figure 5. Microstructure of the welds center under different oscillating frequency and amplitude. (a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude 1.5 mm; (c) oscillating frequency 150 Hz, oscillating amplitude 1.5 mm; (d) oscillating frequency 400 Hz, oscillating amplitude1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
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图6为不同摆动频率和幅度下接头的显微硬度. 与母材相比,熔化区和热影响区发生软化,熔化区硬度值最低,随着远离焊缝中心,热影响区硬度先迅速升高,且在一定范围内变化不大,然后逐渐升高至母材水平. 母材的强化机制为θ′沉淀强化,在远离焊缝的热影响区θ′部分溶解且部分粗化,越靠近焊缝这一现象加剧,硬度逐渐降低,在靠近焊缝的热影响区θ′完全溶解,硬度曲线出现“平台”,该部分强化机制为固溶强化,其效果弱于沉淀强化,而熔化区因发生严重的Cu元素偏析,固溶强化效果被显著削弱,硬度最低[17-18].
图 6 不同摆动频率和幅度下接头的显微硬度
Figure 6. Microhardness of the joints under different oscillating frequency and amplitude.(a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude 1.5 mm; (c) oscillating frequency 150 Hz , oscillating amplitude1.5 mm; (d) oscillating frequency 400 Hz,oscillating amplitude1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
无摆动焊接接头熔化区的平均硬度约为79.0 HV,当摆动频率为150 Hz、摆动幅度为0.5 mm时熔化区平均硬度为80.5 HV,其它摆动焊接接头熔化区平均硬度介于83.2 ~ 84.2 HV之间. 这可能联系于无摆动与摆动参数(摆动频率150 Hz,摆动幅度0.5 mm)下焊缝中心晶粒尺寸相差不大,而其它摆动参数下焊缝中心晶粒更为细小.
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图7为不同摆动频率和幅度下接头的抗拉强度. 未摆动焊接接头的抗拉强度为256 MPa,约为母材强度的55.9%. 当摆动幅度为1.5 mm时,随着摆动频率的升高接头的抗拉强度先升高后降低;当摆动频率为150 Hz时,随着摆动幅度的升高,接头的抗拉强度不断升高;当摆动幅度为2.5 mm时,接头的抗拉强度达到318 MPa,约为母材强度的69.4%. 焊接接头拉伸后全部断裂在熔化区,表明熔化区为接头最薄弱的区域,这与熔化区硬度值最低的结果相一致.
图 7 不同摆动频率和幅度下接头的抗拉强度
Figure 7. Tensile strength of the joints under different oscillating frequency and amplitude. (a) oscillating amplitude 1.5 mm; (b) oscillating frequency 150 Hz
图8为不同摆动频率和幅度下接头断口的宏观形貌. 在接头断口的部分区域出现了大小不均的孔洞,孔洞来源于焊接过程中产生的气孔缺陷. 为了更好地建立接头抗拉强度与气孔缺陷的内在联系,对接头断口的孔洞面积占比进行了统计,如图9所示. 当摆动幅度为1.5 mm时,断口孔洞面积占比随摆动频率的升高先减小后增大;当摆动频率为150 Hz时,断口孔洞面积占比随摆动幅度升高而降低. 图9c为接头抗拉强度与断口孔洞面积占比的对应关系. 接头抗拉强度与断口孔洞面积相关性很强,表现为线性负相关关系. 焊缝中的气孔将直接对接头抗拉强度产生不良影响,当接头中的气孔率越高时,焊缝的有效承载面积越小,接头的抗拉强度越低. 此外,基于线性拟合结果,当焊缝气孔率为0时,接头抗拉强度的预测值为326 MPa,但仍与母材抗拉强度有较大差异. 这是由于相比于母材的沉淀强化作用,熔化区的固溶强化效果较弱,加之Cu元素存在严重偏析. 考虑到不同摆动频率和幅度下焊缝的显微硬度差别不大,因此可以得出焊态接头的抗拉强度主要受制于焊缝气孔率.
图 8 不同摆动频率和幅度下接头的断口宏观形貌
Figure 8. Fracture macroscopic morphology of the joints under different oscillating frequency and amplitude.(a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude 1.5 mm; (c) oscillating frequency 150 Hz, oscillating amplitude1.5 mm; (d) oscillating frequency 400 Hz, oscillating amplitude 1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
图 9 不同摆动频率和幅度下接头的断口孔洞面积占比及与抗拉强度关系
Figure 9. Ratio of fracture hole area of the joints under different oscillating frequency and amplitude as well as corresponding relationship to the tensile strength. (a) oscillating amplitude 1.5 mm; (b) oscillating frequency 150 Hz; (c) relationship between ratio of fracture hole area and tensile strength
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(1) 激光摆动焊接可以降低焊缝气孔率,与摆动频率相比,摆动幅度的增加显著抑制了焊缝气孔的产生. 当激光功率为4 kW、焊接速度为3 m/min、摆动频率为150 Hz和摆动幅度为2.5 mm时,焊缝气孔率从无摆动的8.81%降低到1.66%.
(2) 接头熔化区由α(Al)基体和分布在枝晶间和晶界的α(Al) + θ(Al2Cu)共晶相组成,铜的偏析导致基体中铜含量较少. 无摆动与摆动频率为150 Hz、摆动幅度为0.5 mm时焊缝中心晶粒尺寸相差不大. 当摆动幅度为1.5 mm时,晶粒尺寸随着摆动频率的提高有所细化;当摆动频率为150 Hz,摆动幅度提高到1.5和2.5 mm时,同样存在晶粒细化现象.
(3) 与母材相比,热影响区和熔化区发生软化,靠近焊缝热影响区硬度逐渐降低,随后硬度曲线出现“平台”,熔化区因发生严重的Cu元素偏析,固溶强化效果被显著削弱,硬度最低. 受焊缝晶粒尺寸变化的影响,部分摆动参数下焊缝的硬度略微升高.
(4) 焊接接头全部断裂在熔化区,无摆动焊接接头的抗拉强度为256 MPa,约为母材强度的55.9%,当摆动频率为150 Hz、摆动幅度为2.5 mm时,接头的抗拉强度高达318 MPa,约为母材强度的69.4%. 接头的抗拉强度与断口孔洞面积占比为线性负相关关系,预测无气孔缺陷的接头的抗拉强度为326 MPa. 考虑到不同摆动频率和幅度下焊缝的显微硬度差别不大,焊缝气孔率成为焊态接头的抗拉强度的主要影响因素.
Microstructure and properties of 2219-T651 aluminum alloy welded joint by laser oscillating welding
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摘要: 采用激光摆动焊接技术对2219-T651铝合金进行了不同摆动幅度和频率下的焊接试验,研究了摆动工艺参数、焊缝气孔率和宏观成形、接头组织和性能之间的内在联系. 结果表明,与无摆动焊接相比,激光摆动焊接可以降低焊缝气孔率,尤其随着摆动幅度的增加,当摆动幅度为2.5 mm时,气孔率降至1.66%. 与母材相比,热影响区和熔化区发生软化. 靠近焊缝的热影响区,由于沉淀强化作用的变弱,硬度逐渐降低,直至出现“平台”. 而由α(Al)基体以及枝晶间和晶界α(Al) + θ(Al2Cu)共晶相组成的熔化区,因铜的偏析导致固溶强化效果被削弱,表现出最低的硬度. 此外,部分摆动参数下焊缝晶粒尺寸有所细化,这引起了其硬度的略微升高. 当摆动频率为150 Hz和摆动幅度为2.5 mm时,接头的抗拉强度高达318 MPa,约为母材抗拉强度的69.4%,接头抗拉强度与断口孔洞面积占比呈线性负相关关系,焊缝气孔率是影响焊态接头抗拉强度的主要因素.Abstract: Laser oscillating welding technology was applied to 2219-T651 aluminum alloy under different oscillating frequency and amplitude. The corresponding relationships between the oscillating parameters, the weld porosity, the joints formation, the microstructures and properties of the welded joints were revealed. The results show that compared with laser welding, laser oscillating welding can reduce weld porosity. When oscillating amplitude is set at 2.5 mm, the weld porosity can be decreased to 1.66%. In comparison with base metal, the heat-affected zone and the fusion zone are softened. Due to the weakening of the precipitation strengthening effect, the microhardness in the heat-affected zone near the weld gradually decreases until a “platform” appears. Meanwhile, the fusion zone is composed of α(Al) matrix, α(Al) + θ(Al2Cu) eutectic phase distributed between dendrites and grain boundaries. Because of the diminished solid solution strengthening effect caused by Cu segregation, the microhardness in the fusion remain the lowest. Additionally, the grain sizes of the welds are refined under some oscillating parameters, leading to slight increase in the microhardness. The tensile strength of the welded joint reach the highest 318 MPa under the oscillating frequency of 150 Hz and the oscillating amplitude of 2.5 mm, which is approximately 69.4% of that of the base metal. The tensile strength of the welded joint shows negative linear correlation for the area proportion of fracture pores. The weld porosity is the main factor to affect the tensile strength of the welded joint.
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Key words:
- 2219 aluminum alloy /
- laser oscillating welding /
- weld porosity /
- microstructure /
- mechanical properties
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图 2 焊缝的宏观形貌和X光气孔检测结果
Figure 2. Macroscopic morphology and X-ray porosity test results of the welds. (a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude1.5 mm; (c) oscillating frequency 150 Hz, oscillating amplitude1.5 mm; (d) oscillating frequency 400 Hz, oscillating amplitude1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
图 5 不同摆动频率和幅度下焊缝中心微观组织
Figure 5. Microstructure of the welds center under different oscillating frequency and amplitude. (a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude 1.5 mm; (c) oscillating frequency 150 Hz, oscillating amplitude 1.5 mm; (d) oscillating frequency 400 Hz, oscillating amplitude1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
图 6 不同摆动频率和幅度下接头的显微硬度
Figure 6. Microhardness of the joints under different oscillating frequency and amplitude.(a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude 1.5 mm; (c) oscillating frequency 150 Hz , oscillating amplitude1.5 mm; (d) oscillating frequency 400 Hz,oscillating amplitude1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
图 8 不同摆动频率和幅度下接头的断口宏观形貌
Figure 8. Fracture macroscopic morphology of the joints under different oscillating frequency and amplitude.(a) without oscillating frequency and amplitude; (b) oscillating frequency 50 Hz, oscillating amplitude 1.5 mm; (c) oscillating frequency 150 Hz, oscillating amplitude1.5 mm; (d) oscillating frequency 400 Hz, oscillating amplitude 1.5 mm; (e) oscillating frequency 150 Hz, oscillating amplitude 0.5 mm; (f) oscillating frequency 150 Hz, oscillating amplitude 2.5 mm
图 9 不同摆动频率和幅度下接头的断口孔洞面积占比及与抗拉强度关系
Figure 9. Ratio of fracture hole area of the joints under different oscillating frequency and amplitude as well as corresponding relationship to the tensile strength. (a) oscillating amplitude 1.5 mm; (b) oscillating frequency 150 Hz; (c) relationship between ratio of fracture hole area and tensile strength
表 1 2219-T651铝合金化学成分(质量分数,%)
Table 1. Chemical compositions of 2219-T651 Al alloy
Cu Mn Fe Ti Zn Si Al 6.62 0.27 0.11 0.04 0.04 0.04 余量 表 2 不同摆动频率和幅度下接头宏观成形
Table 2. Formation of joints under different oscillating frequency and amplitude
摆动频率
f/Hz摆动幅度
A/mm熔宽
w/mm熔深
h/mm气孔率
P(%)0 0 3.9 3.6 8.81 50 1.5 4.0 3.4 7.14 150 1.5 4.5 3.2 5.56 400 1.5 4.4 3.1 7.29 150 0.5 4.1 3.7 7.66 150 2.5 4.7 2.7 1.66 表 3 无摆动焊接接头的能谱分析结果(质量分数,%)
Table 3. EDS results of the non-oscillating welded joint
位置 Al Cu 可能相 1 98.14 1.86 α 2 78.45 21.55 α + θ 3 93.09 6.91 α 4 78.17 21.83 α + θ 5 94.42 5.58 α 6 77.64 22.36 α + θ 7 58.66 41.34 θ -
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