Investigation On Laser Fillet Welding Process Of Dissimilar Steel In Automotive Pulley Assembly

Laser welding is a welding method using a high-energy-density laser beam as heat source.Laser welding with high efficiency,small heat-affected zone,can be used to wide range of weldable materials and simple to be automatic applied.However,there are also defections such as high requirements for weldment accuracy,difficult to utilize on highly-reflective materials.At the same time,laser welding application faces many challenges in a variety of complex industrial scenarios and complex process conditions.Therefore,it is necessary to continuously improve its processing/procedure and introduce more innovative technical means cater to the diverse commercial needs.This subject research relies on an automated production project,the fast automated laser fillet welding application project of automobile pulley components,in the field of auto parts production.The research involves laser welding technology on 90° right angle dissimilar steel part.In order to ensure production efficiency,the laser welding rate need to be operated over 100 mm / s.In addition,the characteristics of the dissimilar steel itself lead to welding defects such as splashing in the laser welding process.Thus,it is necessary to adjust the process parameters such as laser power,laser spot oscillating amplitude,laser spot offset amplitude and laser welding speed.Investigating the influence of various parameter changes on macro morphology,microstructure morphology,element migration phenomenon,mechanical properties and fracture morphology of the weld,and obtaining the best process parameters to achieve the adjustment of the macro morphology of the weld,microstructure optimization and improvement of mechanical properties.The specific research contents and conclusions are as follows:(1)The effect of various welding parameters on the macro-morphology of the fillet weld and the hardness distribution of the cross section was studied.The results indicate that the increase of laser power can significantly improve the welding quality.If the laser spot route oscillates with a small amplitude diameter of 0.4 mm,the spattering can be mitigated,and the macroscopic appearance of the weld will be better.However,when the oscillating amplitude diameter expanded up to 0.8 mm,the spattering phenomenon is more intense.Undercut defects occur when the offset of laser spot route exceeds 0.3 mm or the laser welding speed exceeds 110 mm / s.Additional,it is obvious showed by hardness distribution on the weld cross section that the hardness of the melting zone is significantly higher than the hardness of the heat affected zone and the base material on both sides.The hardness distribution tends to be uniform after the introducing of laser spot oscillating amplitude.(2)The influence of various welding parameters on the microstructure of fillet welds was studied.The results demonstrated when the laser power reach 3.6 k W,the structure in the weld fusion zone become fine,and harmful structures such as Weiss structure in the heat affected zone reduces.When the laser spot oscillating amplitude attains to 0.8mm,more Weiss structure is formed in the heat-affected zone near the 40 Cr base metal,and the structure is coarser near the heat-affected zone near the 45 steel base metal.Moreover,it was found that along the depth direction in the weld,the lath martensite decreased while the depth increasing,and the needle martensite content ascended with increasing depth.Through EDS analysis,it was found that the Cr element composite in the weld zone along the direction from 40 Cr base material to 45 steel base material gradually decreased,while the C element content distributes evenly.Simultaneously,no obvious migration and aggregation phenomena were found.(3)The influence of various welding parameters on the mechanical properties and fracture morphology of fillet welds was studied.The results show that the increase of laser power can significantly improve the weld strength.The intensity does not change much with laser beam intensity of 0.4 mm,the laser spot shift the amplitude has little effect on the strength of the weld.While the laser welding speed increased to 120 mm / s will significantly reduce the strength of the weld.From the fracture morphology,both the tensile fracture and the shear fracture are shown as intergranular fractures,and after using the laser rocking process,the fractures are shown as quasicleavage fractures,indicating that the laser spot oscillating process improves the interior of the weld grain boundary strength.(4)Based on the research results above,a set of optimal fillet welding process parameters were determined: laser welding power 3.6 k W,laser spot oscillating amplitude diameter 0.4 mm,laser spot route offset 0.2 mm toward the 40 Cr base material side,laser welding speed is 100 mm / s.Under this welding condition,the research can get better the macro morphology of the weld,least the welding defects,and less harmful structure inside the microstructure.Furthermore,the grains are refined to a certain degree,which meets the industrial application needs of the product.