| 6000series aluminum alloys have been regarded as one of the ideal automobilelightweight materials for good formability, high specific strength, corrosion resistance,high temperature resistance and recycling potential.6000series belongs to Al-Mg-Siseries aluminum alloys, which are strengthened by heat treatment and extremely sensitiveto the change of temperature or composition. The main problems restricting itsapplication in automobile manufacturing include serious oxidation, elements loss,microstructure uniform, hot cracking tendency and decreased strength of weld joint. Inthis paper, the microstructure and properties of6082-T6welding joints were researched.The joints were obtained by a pulsed laser welding machine with high power density,good linear energy controllability and slight welding deformation.The pulsed laser welding process, temperature field distribution and formingcharacteristics of weld joints of6082-T6aluminum alloy were investigated and the stressmodels of molten pool were established. Microstructure of the weld joint without fillerwire, mechanism of defects formation and the preventive measures were discussed aswell. Results proved that metal vapor and welding fumes which dued to the vaporizationof Al and Mg in aluminum alloy were produced during the welding process. The peaktemperature of thermal cycles1mm~8mm distanced from the weld center were1221℃,559℃,559℃,247℃,232℃,203℃,185℃and165℃respectively. A greater peaktemperature gradient and a higher average heating and cooling rate of thermal cycleswere obtained at the points closer to the weld center. The average heating rate andcooling rate of the point1mm distanced from the weld center reached to566.16℃/s and38.44℃/s respectively, the retention time above liquidus temperature was about2.88s to3.26s. Metals in the molten pool were affected by an integrated action of the pulsed laserimpact force, the metal vapor reaction force, the surface tension, the shielding gasblowing force, the clamp restraint force and the gravity. Forms and size of the forces varied with the laser energy. The weld zone of joint welded without filler wire wasconsisted of the coarse columnar grains area formed by a single pulse, the fine equiaxedgrains area formed by multi-pulses and the transition area. The-Al phase solid solutionwas found in the weld zone. The heat affected zone was formed by the solidtransformation zone and the partially melted zone. Weld crater, surface expulsion, hotcracking and porosity were prone to produce in the weld joint without filler wire.Analysis of the parameters’(pulse current, welding speed and pulse waveform)effects on the weld joint forming was done through calculation of single pulse energy,average peak power density and overlapping factor of the laser pulse s. Effects of theprocess parameters produced on the forming of weld joints could be divided into threestages: firstly, incomplete penetration resulted in a semicircle section and the ratio ofdepth/width was0.5~0.7; then critical penetration induced a “V” type section and theratio increased to0.7~0.9; finally, complete penetration led to a “U” type section and theratio decreased to0.7~0.8.Filler wires were added to adjust the weld composition. The weld zone of jointsfilled with wires rich in Si (ER4043and ER4047) consisted of-Al and (-Al+Si)eutectic phase which had a discontinuous distribution at the grain boundary and a smallamount of granular or short rod eutectic distributed in the grain. The weld zone of jointfilled with wire rich in Mg (ER5356) consisted of-Al and Mg2Si intermetalliccompounds. The tensile strength of the joints welded with filler wires increased by73%~180%compared with joints without filler wire. Results showed that the tensilestrength of joint with ER4047was234.26MPa,69.19%of the base metal, showing theductile fracture characteristics. The tensile strength of joint with ER4043was207.79MPa,61.37%of the base metal. The tensile strength of joint with ER5356was144.18MPa,42.58%of the base metal, showing a mixed of brittle and ductile fracture. |
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