Study on microstructure and properties of 5mm thick copper laser welded joints
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摘要: 为了研究离焦量对5mm厚紫铜激光焊接焊缝成形的影响和组织特征及性能，采用金相显微镜对焊缝组织及形貌进行分析，并对接头进行了拉伸及电导率测试。结果表明，在高离焦量绝对值时，易出现飞溅并造成焊缝表面孔洞，在离焦量0mm~-2mm范围内可获得成形良好的焊缝；焊缝纵截面柱状晶与焊接方向的角度由两侧的90°逐步降低为中间的0°，靠近焊缝上表面的柱状晶长度约为靠近下表面的柱状晶长度2.96倍，热影响区晶粒发生粗化，且离焦量+1mm对应的热影响区宽度最大；焊透情况下的不同离焦量对应的接头拉伸强度相当，可达母材的77.3%，离焦量0mm~-1mm对应的接头延伸率略高于离焦量-1mm~-4mm对应的接头延伸率，可达母材的54.9%；焊缝的电导率与母材几乎一样。该研究有利于获得成形良好的紫铜激光焊接接头。Abstract: In order to study effect of defocus amount on the weld formation, the microstructure characteristics and properties of 5mm thick laser welding copper, metallographic microscope was used to analyze the microstructure and morphology of the weld.The tensile strength and electrical conductivity of the joint were tested.The results show that, when the absolute value of defocus is high, it is easy to spatter and cause holes on the weld surface.A well-formed weld can be obtained within the defocus range of 0mm~-2mm.The angle between the columnar crystal and the welding direction of the longitudinal section of the weld is gradually reduced from 90°on the sides to 0°in the middle.The columnar crystal near the upper surface of the weld is about 2.96 times the length of the columnar crystal near the bottom surface.The grain size of heat affected zone coarsen.And the width of heat affected zone corresponding to defocus+1mm is the largest.Under the penetration condition, the tensile strength of the joints corresponding to the different defocus amounts is equal, up to 77.3% of base metal.The joint elongation with defocus 0mm~-1mm is slightly higher than that with defocus-1mm~-4mm, up to 54.9% of base metal.The electrical conductivity of the weld is almost the same as that of the base metal.The study is beneficial to obtain good shaped laser welded joints of copper.
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Keywords:
- laser technique /
- laser welding /
- copper /
- weld formation /
- microstructure /
- properties
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Figure 3. Appearance of laser welded copper joints with different defocus amounts
a, c, e, g, i, k, m, o—positive of weld bead b, d, f, h, j, l, n, p—back of weld bead
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Figure 7. Microstructure morphology of longitudinal section of weld bead
a—sketch of observation position b—near to upper surface c—near to lower surface
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Figure 8. Fracture morphologies of copper
a—low magnitude of fracture morphology of base metal b—high magnitude of fracture morphology of base metal c—low magnitude of fracture morphology of weld metal of sample 4# d—high magnitude of morphology of weld metal of sample 4# e—low magnitude of fracture morphology of weld metal of sample 7# f—high magnitude of morphology of weld metal of sample 7#
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Figure 10. Relationship between electrical conductivity and distance from weld center line
Table 1 Chemical compositions (mass fraction) of the materials
elements Cu O Fe S Ni mass fraction ＞0.9990 ＜0.0006 ＜0.00005 ＜0.00005 ＜0.000008 
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Table 2 Laser welding parameters
sample No. defocusing distance/mm 1# +3 2# +2 3# +1 4# 0 5# -1 6# -2 7# -3 8# -4
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Table 3 Tensile properties of welded joints
sample No. defocusing
distance/mmtensile
strength/MPaelongation/% fracture
locationbase metal 295 19.1 base metal 3# +1 192 10.5 weld 4# 0 214 10.0 weld 5# -1 218 7.0 weld 6# -2 228 8.0 weld 7# -3 215 7.0 weld 8# -4 211 5.5 weld
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