| 6016 aluminum alloy is widely used in lightweight car body manufacturing.In this dissertion,laser welding of 6016 aluminum alloy with filler wire is carried out.The effects of process parameters on weld forming are studied,and then microstructure and mechanical properties at different welding parameters are discussed.The influences of aging on the microstructure and mechanical properties of welded joints are investigated by observing the precipitation characterizations in weld seams.The effects of parameters such as wire feeding direction,defocusing distance,laser-wire distance,laser power,wire feed rate and welding speed have been studied.The experiment results show that the optimal welding parameters are as follows:it's filler wire leading method;laser-wire distance is 0.6mm;defocusing distance is within 0+5mm;laser power is between 2.5kW and 3.5kW.Each laser power has a stable range of welding speeds.In this study,at laser power 3kW the welding speeds range is the widest from 3.2m/min to 4.2m/min.Wire feed rate is set as 1.2 times of welding speed.The exprimental results show the grains in center of weld zone are fine and homogenious whose sizes are about 12?m.The size of HAZ is as narrow as 1.2mm since laser welding has smaller heat-input.The second phases on the grain boundry are analyzed to be Mg2Si,Al5FeSi and AlCuMgSi.As heat input increases from 45J/mm to 60J/mm,the average grain size of equiaxed grains increases from 6.5?m to 10.05?m,the average spacing in columnar grains also increases from 6.73?m to 10.8?m,and tensile strength decreases from 226MPa to 209MPa.The hardness and tensile strength of the welding joint both increase firstly and then decrease with the extension of aging time,who reach the maximum in 10h.The microstructure of weld seam is observed to become uniform gradually by optical metallographic microscope.Eutectic phases don't dissolve in matrix after ageing researched by SEM.The TEM test shows there is no precipitation before aging.A small quantity of precipitation formed in the alloy when aging at 180?for 2h,who are verified to be Q'and L phases.After aging for 6h at 180?,lamellar?'phases are observed with a cross section of about 13×7nm2 and50nm in length.Needle-like?"phases,about 2×3nm2 in cross-section and50nm in length,are present in the alloy after 10h annealing time at 180?.The elongated?"phases are aligned to one of the<100>Al directions.The results show aging behavior of weld seam is different from base metal.The precipitation forming in aging enhances strength and improves hardness of weld seam. |
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