Research Of Process And Structure Property On CMT Welding-brazing Of Aluminum/Steel With Intermediate Interlayer Plumbum

In this paper,5052aluminum alloy and galvanized Q235steel sheets with thickness of1mm were lap welded by cold metal transfer technology (CMT) with ER4043as the fillerwire and plumbum (Pb) as the intermediate interlayer. Scanning electron microscope(SEM),energy dispersive spectrometer(EDS), microscope with super-depth, X-raydiffraction(XRD), electronic universal tensile testing machine and hardness tester wereemployed to study the microstructure, phase composition, chemical component, andmechanical properties of the joint. So we get following conclusion.While the intermediate interlayer were not used in the experiment, the best weldingparameters were obtained through single variable experiment. The tensile strength is128.8MPa when welding current is55A, welding speed is650mm/min and pulse frequencyis3Hz. Lack of fusion were appear in the root of weld when heat input is low and thisphenomenon will disappear with the increase of heat input. Width of weld increase with theincrease of heat input. The lower the heat input, the narrower the width of weld. Much porewere appear within the weld and them mostly concentrated in top of fusion zone ofaluminum side. The heat input has a large effect on size of cross section of joints. And sideof cross section of joints has a large effect on tensile strength of joints.While the intermediate interlayer were used in the experiment, the best weldingparameters were obtain through orthogonal experiment. The tensile strength is167.4MPawhen welding current is60A, welding speed is450mm/min and pules frequency is5Hz.According to the microstructure characteristic of welded/brazed joint, the joint can bedivided into following areas: unmelted galvanized steel, aluminum alloy base metal,interface zone(edge of interface zone and center of interface zone), fusion zone, HAZ, zincand rich zone.The grains of HAZ became bulky due to effect of heat, microstructure of fusion zone isbulky columnar crystal and branch crystal belong to melting zone. Melting zone consist ofbranch crystal and secondary phase particles. Branch crystal is α-Al solid solution andsecondary phase particles in the boundary of grains is Al-Si eutectic. Zinc rich zone consistof α-Al solid solution, Al-Si eutectic and litter Al-Zn eutectic. Much secondary phase crystalwere appear in the boundary of grains of fusion zone, this particles make the hardness offusion zone increase. So the hardness of fusion zone is higher than the hardness of base metal. When tensile strength is extreme small, the lap joint broken in interface ofaluminum and steel. In other case, the lap joint broken in HAZ. Fracture of joint belong tomixed fracture pattern which include much ductile fracture and extreme little brittle fracture.A intermetallic compound(IMC) layer were produced in the interface of aluminum andsteel. The main component of IMC layer were Fe2Al5and FeAl. The thickness of IMC layerhas a large effect on tensile strength of joint. The effect of intermediate interlayer mainlycontain fallowing aspect: a) Increase the wettability of liquid metal on the surface of steel. b)Improve the tensile strength of welded/brazed joint. c) Effectively block the diffusionbetween Fe atoms and Al atoms, thus avoiding generating plenty of Fe-Al IMC. d) Theaddition of Pb element enhance the plasticity of FeAl intermetallic compound.