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试验采用的焊接材料为A7N01铝合金板,规格为150mm×75mm×6mm,焊丝采用ER5356铝合金焊丝,直径1.2mm。母材及焊丝成分如表 1所示。
Table 1. Chemical compositions of A7N01 aluminum alloy and ER5356 welding wire (mass fraction)
element Al Si Fe Cu Mn Mg Cr Zn Ti 7N01 balance 0.0030 0.0035 0.0020 0.0070 0.0200 0.0030 0.0500 0.0020 ER5356 balance 0.0025 0.004 0.0010 0.0020 0.0450 0.0010 0.0010 0.0006 -
在6mm厚的7N01铝合金试样板上进行激光-MIG焊接试验,通过改变焊接工艺参量,研究激光功率和焊接速度对焊缝成形的影响关系,试验工艺参量如表 2所示。试验中通过改变激光功率和焊接速度,探究其对焊缝熔宽、熔深、余高以及宏观形貌的影响。此外,为优化焊缝成形,得到表面成形良好,并且底部成形连续的焊缝,焊接试样板底部采用纯铜衬垫板。3种坡口形式如图 1所示。分别是:Y型60°坡口,3mm钝边;Y型30°坡口,3mm钝边;I型坡口,0.5mm间隙。
Table 2. Welding test process parameters
numbering groove type laser power/
kWwire feed speed/
(m·min-1)welding speed/
(m·min-1)arc power/
kWline energy/
(kJ·m-1)1# no groove 2.5 8.5 0.9 2.812 354.13 2# 3.5 8.5 0.9 2.812 420.80 3# 3.0 8.5 0.9 2.812 387.47 4# 3.0 8.5 1.2 2.812 290.60 5# 3.0 8.5 0.75 2.812 464.96 6# Y-shaped 60° 3.0 9.0 1.0 3.028 361.68 7# Y-shaped 30° 3.0 9.0 1.0 3.028 361.68 8# 0.5mm clearance 3.0 9.0 1.0 3.028 361.68 Figure 1. Groove form a—Y-shaped 60°, 3mm blunt edge b—Y-shaped 30°, 3mm blunt edge c—I-shaped, 0.5mm clearance
为尽量避免气孔、夹杂等缺陷,焊前对试样板进行酸碱洗,用刮刀清理母材表面的氧化膜,之后用无水乙醇清洗母材表面,清除表面油污。焊后沿垂直于焊缝方向制备金相试样,经打磨抛光后用Keller试剂进行腐蚀(Keller试剂配比为V(HF):V(HCl):V(HNO3):V(H2O)=2:3:5:90)。在金相显微镜下,观察焊缝截面,并测量熔深与熔宽和余高。采用GP-TS2000M型拉伸机,进行接头拉伸测试,拉伸试样尺寸如图 2所示。焊缝截面示意图如图 3所示,显微组织选取位置如图 3中的A, B, C, D点位置,其中焊缝转折点为激光与电弧焊接作用区域分界线,由于焊接底部,采用纯铜衬垫板强制成形,故由焊缝转折点深度,代替焊缝熔深做近似分析。图中虚线为硬度打点位置,分别在焊缝转折点、近上表面、近下表面距焊缝转折点1.5mm处。
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激光-MIG复合焊接试验的焊接系统,主要由激光器、机器人(KUKA KR60)、MIG焊机组成,如图 4所示。激光器为Trumpf-Trudisk 10002型碟片激光器,如图 5所示。激光波长为1030nm,最大连续输出功率为10kW,光束质量为8mm·mrad,功率稳定性±1%,准直焦距200mm,聚焦焦距300mm,传输光纤芯径400μm。保护气采用纯度99.99%的氩气,气体流量为14L/min。焊接过程中,采用激光前置的方式,激光与电弧夹角为35°,离焦量为-2mm,光丝间距为1mm。试验过程中的电弧输出采用一元化控制。
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将拉伸试件按照GB/T16865-2013的检测标准,在拉力试验机上进行拉伸试验,其在不同焊接参量下平均抗拉强度及延伸率如表 3所示,用Origin绘制柱状图如图 11所示。可见,6种焊接参量下平均抗拉强度相近,均在260MPa~280MPa范围内,拉伸性能比较稳定,平均抗拉强度为271MPa,达到母材的60%;平均断后伸长率为4.3%,达到母材的48%。其断裂位置均在焊缝中心位置,如图 12所示。分析为铝合金在进行激光-MIG复合焊接时,气孔主要集中在焊缝中心以及熔合线附近,其中焊缝中心的大直径不规则气孔,对抗拉强度及焊后延伸率的影响较大,焊缝中心及熔合线附近的气孔是焊接接头的薄弱位置,易发生断裂。
Table 3. Average tensile strength and elongation after fracture under each welding parameter
numbering 3# 4# 5# 6# 7# 8# average base metal tensile strength Rm/MPa 280 266 268 275 265 270 271 454 break elongation A/% 4.0 4.5 5.5 4.5 3.5 4.0 4.3 9.0 -
对于优化后的接头,沿垂直焊缝方向在近上表面、焊缝转折点、近下表面3种不同位置测量接头硬度,硬度值的分布如图 13所示。由图可见,3种位置处的显微硬度分布特征相似,整体上呈“U”型分布,在焊缝中心硬度较低,在熔合线附近硬度陡然上升,到母材硬度趋于平稳,母材硬度均值为109.2HV。此外,近上表面焊缝中心位置的平均硬度为87.3HV,中部及近下表面焊缝中心位置的平均硬度为83.6HV,略低于近上表面的硬度,整体焊缝平均硬度为85.4HV。这是因为激光匙孔”失稳在焊缝中部及底部易产生气孔,气孔附近的硬度较低,使底部焊缝平均硬度减小;另一方面,由于焊缝底部强制成形的衬垫板,阻碍了熔池底部金属液体的流动,使焊缝底部组织分布不均,从而降低了硬度。
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A7N01铝合金激光-MIG复合焊接接头微观组织,如图 14所示。母材区晶粒为平行于轧制方向的带条状组织,晶粒分布均匀,如图 14a所示。热影响区靠近熔合线的晶粒,由于受热循环作用,使晶粒发生了一定程度的长大,但仍保留了条带状组织的基本特征,其组织末端与母材区分不明显。由于该区受热会析出固溶相,其硬度强度会有所降低,塑性增加,如图 14b所示。焊缝熔合区组织如图 14c所示,该区域位于焊缝边缘,温度梯度较大,在熔合线靠近焊缝方向,形成了垂直于熔合线的粗大柱状晶组织,并沿焊缝中心向等轴晶区转变。由于激光-MIG复合焊接的熔池冷却速度快,其内部由于氧化物夹杂和微量水分子而产生的氢气泡短时间来不及溢出,易产生工艺类氢气孔,严重影响焊缝性能和质量。图 14d为焊接接头的焊缝区,由图可知,焊缝区组织属于典型的急冷铸态组织,母材与焊丝熔化后在焊缝中心形成等轴晶,该区易产生冶金类气孔。
A7N01铝合金激光-MIG复合焊接焊缝成形与组织性能研究
Study on weld formation and microstructure of A7N01 aluminum alloy by hybrid laser-MIG welding
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摘要: 为了研究工艺参量对激光-MIG复合焊接的焊缝成形和组织特征及性能的影响,针对6mm的A7N01铝合金板,采用不同的激光功率、焊接速率和坡口形式,进行了激光-MIG复合焊接试验,观察焊缝成形及接头微观组织,并对其性能进行测试。采用Y型30°坡口,在激光功率3.0kW、焊接速率1.0m/min的参量下进行激光-MIG复合焊接时,焊缝表面成形良好,底部成形连续;接头平均抗拉强度为271MPa,达到母材的60%;焊缝中心硬度为85.4HV,达到母材的78%。结果表明,随着激光功率的提高,焊缝熔深呈线性增大;焊接速率越大、焊缝熔宽和熔深越小,余高略有增加;焊接接头对不同坡口形式的适应性良好;接头中热影响区晶粒粗化,硬度降低,熔合区晶粒为树枝晶,易产生工艺类氢气孔,焊缝中心晶粒为等轴晶。该研究有利于获得成形良好的A7N01铝合金激光-MIG复合焊接头。
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关键词:
- 激光技术 /
- 激光-MIG复合焊接 /
- A7N01铝合金 /
- 焊缝成形 /
- 力学性能
Abstract: In order to study the effect of process parameters on weld formation, microstructure characteristics, and properties of the joint welded by laser-melt inert-gas (MIG) hybrid welding, laser-MIG hybrid welding of 6mm A7N01 aluminum alloy plates was carried out with different laser powers, welding speeds, and groove forms. The microstructure and properties of the joints were observed and tested. The results show that as the laser power increases, the weld penetration increases linearly. Furthermore, the higher the welding speed, the smaller the weld width and the penetration depth, and the margin is slightly increased. The welded joints have good adaptability to different groove forms. When the hybrid laser-MIG welding was carried out with the laser power of 3.0kW, welding speed of 1.0m/min, and the Y-shaped 30° groove, the sound joint was obtained. The average tensile strength of the joint is 271MPa, which is 60% of the base metal. The center hardness of the weld is 85.4HV, which is 78% of the base metal. In the joint, the grain in the heat-affected zone is coarsened, the hardness is reduced, and the grain in the fusion zone is dendritic grain, which is easy to produce hydrogen holes in the process. In addition, the grain is equiaxed at the center of weld. This research is conductive to obtaining a well-formed laser-MIG hybrid welding joint of A7N01 aluminum alloy. In addition, the grain is equiaxed at the center of weld.-
Key words:
- laser technique /
- laser-MIG hybrid welding /
- A7N01 Al alloy /
- weld formation /
- mechanical properties
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Table 1. Chemical compositions of A7N01 aluminum alloy and ER5356 welding wire (mass fraction)
element Al Si Fe Cu Mn Mg Cr Zn Ti 7N01 balance 0.0030 0.0035 0.0020 0.0070 0.0200 0.0030 0.0500 0.0020 ER5356 balance 0.0025 0.004 0.0010 0.0020 0.0450 0.0010 0.0010 0.0006 Table 2. Welding test process parameters
numbering groove type laser power/
kWwire feed speed/
(m·min-1)welding speed/
(m·min-1)arc power/
kWline energy/
(kJ·m-1)1# no groove 2.5 8.5 0.9 2.812 354.13 2# 3.5 8.5 0.9 2.812 420.80 3# 3.0 8.5 0.9 2.812 387.47 4# 3.0 8.5 1.2 2.812 290.60 5# 3.0 8.5 0.75 2.812 464.96 6# Y-shaped 60° 3.0 9.0 1.0 3.028 361.68 7# Y-shaped 30° 3.0 9.0 1.0 3.028 361.68 8# 0.5mm clearance 3.0 9.0 1.0 3.028 361.68 Table 3. Average tensile strength and elongation after fracture under each welding parameter
numbering 3# 4# 5# 6# 7# 8# average base metal tensile strength Rm/MPa 280 266 268 275 265 270 271 454 break elongation A/% 4.0 4.5 5.5 4.5 3.5 4.0 4.3 9.0 -
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