Research On Laser Welding Technology Of Auto Aluminum/Steel Dissimilar Material Robot

It has become the developing trend that the aluminum/steel integrated structure will replace the single steel structure in automotive industry because of the lightweight demand of automobiles.This study selected the automotive sheet 6016aluminum alloy and DC06 low carbon steel flat specimen as the test material,and used the fiber laser to carry out the laser welding process and mechanism on the steel-on-aluminum overlapped configurationThe effects of laser power?P?,defocusing distance?f?and welding speed?V?on the surface forming,microstructure and interface structure of laser lap welding joint of Al/steel were studied.According to the experimental results,a good weld with silver-white metallic luster,no porosity,cracks and unfused defects can be obtained under appropriate process parameters.There were two main morphological characteristics of IMC at the weld/aluminium interface.The layered IMCs phase were Fe₃Al,FeAl and FeAl₂,which close to the weld and the needle-like IMC phase was FeAl₃,which close to the aluminum side.When the laser power was 800W,defocusing distance was+2mm and welding speed was 0.07m/s,a large number of ferrite and pearlite with good plasticity and toughness were formed in the upper part of molten pool.The IMCs of weld/aluminium interface were mainly layered FeAl₂and fine needle FeAl₃.With the increase of laser power or the decrease of welding speed,the penetration and width of aluminium side increased,and the number of IMC increased,which showed that the thickness of layered IMC increased and the size of needle IMC increased.When the defocusing distance decreased,the penetration depth and width of aluminium side increased,and the number of IMCs in interface layer increased.When the laser power was 800W,the welding speed was 0.07m/s and the defocus distance was+2mm,the Al alloy/steel joint held a maximum average tensile shear strength of 81.3N/mm.Under these conditions,the fracture occured in HAZ and FeAl₂ phases of aluminium base metal,showed a ductile fracture mode.The effect of alloying elements on the microstructure and interface structure of laser overlap welding of Al/steel was studied.Under the conditions of the laser power was 900W,defocusing distance was+2mm and welding speed was 0.07m/s.Compared with that without powder,The penetration depth and width of aluminium side increase,but the increase of penetration depth is smaller with the addition of AlSiCu powder.With the increase of Mo powder content from 1%to 5%,the aluminium side melting depth increased gradually,the melting width increased first and then decreased,reaching the maximum when the content of Mo was 3%.After powder addition,the grain size in the weld zone was refined and gradually transformd from columnar grain to fine equiaxed grain.The weld/aluminum interface was flat and the number of IMCs were small.When 3%Mo powder was added,the layered IMCs had the smallest thickness of about 3-10?m.After adding AlSiCu+3%Mo powder,Al alloy/steel joint held an average tensile shear strength of 82.3N/mm,which is 25%higher than that the same welding parameters without adding powder.and the joint fracture occured in the heat-affected zone of the aluminum alloy,showed ductile fracture.