Research On Microstructure And Mechanical Property Of Welding-brazing Butt Joint Of Aluminum/Steel By Micro-beam Plasma Welding

In the butt welding of aluminum and steel dissimilar metals,there are some problems with the poor spreading,the brittle intermetallic compounds and the low quality joint due to the great difference in thermal and physical properties between aluminum and steel.Aiming at above these problems,two measures of controlling welding heat input and adding alloying elements are considered.In this paper,the micro-beam plasma butt welding-brazing experiment of 6010 aluminum alloy and ST04Z galvanized steel was carried out with the micro-beam plasma arc advantages of high stiffness,good stability and low residual stress.The morphology,interface microstructure and mechanical property of aluminum/steel joint were analyzed by adding Al-B binary alloy powder,AlCrFeNiCo multi-principal high entropy alloy powder,ER4043 wire.The effects of welding process parameters on the spreading of joint and the thickness of intermetallic compound layer were investigated.The regulation function of different filler materials on interface between aluminum and steel was studied.The growth process of intermetallic compounds at aluminum/steel interface was simulated by means of Monte Carlo?MC?and Cellular Automaton?CA?,which was to investigate the growth mechanism of intermetallic compounds and the factors affecting the thickness of intermetallic layer.The experiment and simulation results show that a good joining between aluminum and steel can be obtained using micro-beam plasma welding-brazing method,and a good spreading width is got in back and front sides of we ld joint.When the binary alloy powder of Al-B is used for the micro-beam plasma butt welding-brazing of aluminum and steel,a joint with one-sided welding and double-side forming can be obtained,and there are no obvious crack,pore,slag in the joint.The intermetallic compound Fe₂Al₅ is formed at the vertical interface,which is serrated near the galvanized steel side and is flocculent or need-like near the weld side.The tensile results show that the joint breaks at the vertical interface and weld spreading,and the fracture form of joint is ductile-brittle fracture.When welding current is 38.5A and welding speed is 80mm/min,the tensile strength of weld joint is193 MPa,which can reach 79%of Al base metal.It is found that the tensile strength of joint is affected by the thickness of intermetallic compound layer and the spreading width of weld seam.When the AlCrFeNiCo multi-principal high entropy alloy powder is used for the micro-beam plasma butt welding-brazing of aluminum and steel,a joint with one-sided welding and double-side forming can be also obtained,and there is a good spreading.A serrated intermetallic compound Fe₂Al₅ is formed near the side of galvanized steel and a flocculent complex phase contained Al,Fe,Co elements is formed near the weld side.The tensile results show that the joints break at interface and the fracture form of joint is ductile-brittle fracture.When welding current is 37A and welding speed is 100mm/min,the tensile strength of weld joint is 170 MPa,which can reach 70%of Al base metal.ER4043 filler wire is used to the welding of aluminum and steel dissimilar metal,and a joint with one-sided welding and double-side forming is also obtained.The back spreading is much greater than front spreading due to the influence of force and filler metal.The intermetallic compound layers of Fe-Al and Fe-Al-Si are formed at the interface,the intermetallic compound is Fe₂Al₅ near the galvanized steel side,the intermetallic compound is FeAl₃ near the weld seam side,and the flocculent ternary intermetallic compound Al₁₂FeSi is formed near FeAl₃ and grows to the weld seam.Compared with preplace powder,the addition of ER4043 wire can effectively inhibit the growth of intermetallic compounds and obtain the smaller intermetallic com pound layer of aluminum/steel.According to the analysis results,elements of Al?Si?Zn are distributed in the toe of weld,the content of Zn element is more and Zn element enriches in the weld zone.The tensile results show that the joint breaks at the interface,the fracture is ductile-brittle mixed fracture.When welding current is 32A,welding speed is 110mm/min and wire feed speed is 122mm/min,the tensile strength of the joint can reach 172 MPa and is 71%of Al base metal,which is higher than the tensile strength of joint obtained from the preplaced alloy powder under the same heat input.The comparative analysis is done about the welding-brazing joints of aluminum/steel using different filler metals.The results show that t he wettability of liquid metal on steel surface can be improved by adding Al-B alloy powder,AlCrFeNiCo high entropy alloy powder and ER4043 welding wire,and the effect of AlCrFeNiCo high entropy alloy powder is more obvious under same heat input.In the micro-beam plasma welding-brazing process of aluminum/steel,the intermetallic compound Fe₂Al₅ is mainly formed at the interface,and ER4043 wire has the most obvious inhibitory effect on the growth of intermetallic compounds.The tensile strength of joint adding ER4043 wire is higher than that of the preplace alloy powder weld joint under same heat input.The results show that it is necessary to control the thickness of intermetallic compound layer and the spreading width of weld seam in order to obtain a good aluminum/steel welding-brazing butt joint.The simulation results show that the growth of the intermetallic compound layer is linear with the time of 0.5 times in the aluminum/steel welding process.The thickness of Fe₂Al₅ phase is most sensitive to the peak temperature,while the effects of cooling time and the temperature gradient of?001?[100]direction are limited for the thickness of Fe₂Al₅ phase.