Study On CMT Welding Technology Between Aluminum Alloy And Galvanized Steel

In this paper,5052aluminum alloy and Q235hot dip galvanized steel were usedfor the base materials with thickness of1mm, ER5356and ER4043were employedfor the filler metal. The CMT welding process was employed to achieve sound jointbetween5052aluminum alloy and galvanized steel thin sheet. The microstructuresand properties of the joints were observed by Keyence VHX-900Digital Microscopeand JSM-6480SEM which is coupled with energy dispersive spectrometer （EDS）.The optimal welding parameters which were suitable for welding aluminiumalloy and steel with Al-Mg filler metal were gained by a lot of experiment, as follows:blowtorch was at the centre of the weld, welding speed of750mm/min, wire feed rateof4.1m/min, welding current of65A, welding voltage of12.5V, and collaborativepulse parameters F=OFF. By the same method, for Al-Si filler metal, the optimalwelding parameters were welding current of65A and welding speed of750mm/min.Under the optimum parameters with ER5356filler metal, the maximum tensilestrength of joint was31.23MPa. The fracture located in the interface area ofaluminum and steel, and didn’t meet the usability requirements. Microhardness testingshowed that the hardness of interface zone could achieve360HV because of thegenerating of hard Al-Fe intermetallic compounds. The microstructures analysisresults of welding joint showed that the joint could be divided into three zones,melting zone, interfacial zone and zinc-rich zone. Melting zone mainly consisted ofα-Αl and β（Mg5Al8）. The phase of interfacial reaction layer was needlelike FeAl₃andFe₂Al₅intermetallic compounds, the thickness of compound layer had the relationshipwith the heat input, so the thickness of compound layer in the centre interface wasbigger than that in the edge interface. Zinc-rich zone was characterized with graydendrites α-Al solid solution and black interdendritic matter Al-Zn eutectoid. At thesame time, the microstructures in heat affected zone of steel had certain refinement.Under the optimum parameters with ER4043filler metal, the maximum tensilestrength of joint achieved115.7MPa.The fracture located in the HAZ of aluminumalloy, and the fracture mode was ductile fracture primarily mixed with the brittlefracture. Microhardness testing showed that the hardness of interface zone wassignificantly higher than the aluminum and galvanized steel substrate, up to460HV.The microstructures of welding joint with Al-Si filler wire had related to the heat input. When the welding current was66A, melting zone mainly consisted of α-Αl anda few Al-Si eutectics; when the welding current increased to113A, melting zone wasmainly composed of α-Αl solid solution, a lot of flake Al-Si eutectic and the long stripof Al-Si eutectic generated in the melting zone near the centre interface area. With theheat input increasing，the grains growth in aluminum HAZ were not obvious. Thecompounds generated in the soldering joint area mainly were FeAl₃, FeAl₂, FeAl andFe₂Al₅, and the closer to the aluminum substrate was, the higher the Al content was.Stoma defects are easy to appear in aluminum alloy welding process. The reasonof producing porosity is that the aluminum alloy had the high thermal conductivity,molten pool had a higher cooling speed, hydrogen and zinc steam which dissolved inthe weld metal at high temperature had no enough time to escape and remained in theweld, in the course of molten pool rapid solidification process.