Laser Welding Of Q235 Steel With Beam Oscillation And Hot Wire

Laser hot wire welding has the advantages of low heat input,high energy utilization,high filler efficiency,and excellent gap bridging capability,but it still faces problems such as poor weld formation and process instability caused by fluctuations in the laser-wire distance.The organic combination of laser beam oscillation and hot wire is expected to improve the above problems by regulating the melt pool behavior,increasing the gap bridging capability of the joint to improve it is industrial adaptability.To this end,this paper carried out laser welding with beam oscillation and hot wire process study on Q235 low carbon steel.The results are as follows:Firstly,comparison of laser hot wire welding and cold wire welding process characteristics,the effects of welding speed,filler wire rate,hot wire current and other major process parameters on the weld formation and process stability were studied systemically.When the laser power is 1.8 k W,the hot wire weld penetration depth increases by 7.5%?16.0% compared to cold wire welding(hot wire current 100 A,welding speed1.0?2.2 m/min);when the hot wire current increases from 0 A to 150 A,the weld penetration depth can be increased from 3.09 mm to 3.48 mm,an increase of 12.6%.However,both laser cold wire welding and hot wire welding are subject to forming defects such as spatter,holes and poor fusion due to the impact of the wire on the molten pool and keyhole.Based on the experimental results of laser hot wire welding,laser welding with beam oscillation and hot wire process study was carried out to investigate the effect of beam oscillation on weld formation.It was found that beam oscillation had a significant effect on improving weld formation and was able to increase the gap bridging ability to 1.3 mm for a given parameter,which was 30% higher than that of laser cold wire welding.When the oscillating amplitude(A)was 0.4?0.8 mm and the oscillating frequency(f)was increased to 100 Hz,the beam oscillation was able to improve defects such as spatter,holes and poor fusion by homogenizing the energy distribution.However,when A was increased to 1.0 mm,the laser energy was distributed significantly higher on both sides than in the center,causing localized overheating of the melt pool on both sides,which instead led to poor wetting forming defects instead.The optimized parameter range for high-quality welds was obtained:0.4 mm?A?0.8 mm and 100?f?200 Hz.The fusion zone of the laser cold wire,laser hot wire and oscillating laser with hot wire welds were found to have no significant difference in microstructures,and all consisted of ferrite and pearlite,while the coarse grain zone of the heat affected zone consisted of proeutectoid ferrite,ferrite side plate and pearlite,and the fine grain zone and incompletely recrystallized zone consisted of granular ferrite and pearlite.Compared with laser cold wire welds,the average microhardness of the fusion zone of laser hot wire welds increased by18 HV to 195 HV.The increase in the average microhardness of the fusion zone of oscillating laser with hot wire welds was not significant,but the microhardness of the fusion zone was most uniformly distributed,with a maximum difference of 24.6 HV,which was only 65% of that of cold wire welding;the standard deviation was 7.7,which was only 58%of that of cold wire welding.This is because laser beam scanning enhances melt pool stirring and promotes solute diffusion in the melt pool,which can suppress weld element segregation.With the optimized hot wire current(100 A),the tensile strength of the welds increased by 8.7% to 574.7 MPa compared to the laser cold wire welding,while the elongation increased by 44.8% to 8.4%.By laser beam oscillation,the tensile strength of the weld is not significantly increased compared to the laser hot wire welding,but the elongation is significantly increased.At the optimized scanning parameter(A=0.6 mm,f=100 Hz),the tensile strength of the oscillating laser with hot wire is basically the same as that of the hotwire welding,but the elongation is increased by 56.0% to 13.1%.The beam oscillation facilitates the breakage of columnar grain in the fusion zone and promotes the formation of finer equiaxed grain,which improves the weld toughness.