To　improve　interfacial　inhomogeneous　temperature　distribution　and　weld　appearance　of　butt　welding-brazing　of　steel/aluminum　dissimilar　metals,　a　hybrid　heat　source　method　combining　laser　penetration　welding　with　CMT　arc　was　developed.　The　Ni/Zn　double　coating　was　prepared　on　the　surface　of　steel　to　improve　the　interfacial　reaction　and　achieve　fluxless　process.　The　welding　characteristics　of　bare　steel/aluminum　alloy,　Ni　coated　steel/aluminum　alloy,　and　Ni/Zn　double　coated　steel/aluminum　alloy　were　comparatively　studied.　Transmission　electron　microscope　(TEM),　scanning　electron　microscope　(SEM),　and　energy　dispersive　spectrometer　(EDS)　were　used　to　analyze　the　interfacial　microstructures　of　the　joint.　The　results　showed　that　the　fluxless　process　were　implemented　by　preparing　Ni/Zn　double　coating　on　the　surface　of　steel.　The　interfacial　reaction　between　liquid　Al　and　solid　steel　was　obstructed　to　some　extent　by　Ni/Zn　double　coating.　The　thickness　of　intermetallic　compounds　(IMCs)　was　reduced　significantly.　The　interfacial　reaction　layer　consisted　of　Fe2Al5　near　the　steel　side　and　Fe4Al13　near　the　aluminum　side.　No　continuous　Ni-Al　IMCs　were　found　at　the　Fe/Al　butt　interface.　The　maximum　tensile　strength　of　Ni　coated　steel/aluminum　joint　was　up　to　93.4　MPa,　which　increased　by　12%　than　that　of　the　bare　steel/aluminum　joint.　The　maximum　tensile　strength　of　Ni/Zn　double　coated　steel/aluminum　joint　was　up　to　112.6　MPa,　which　increased　by　35%　than　that　of　the　bare　steel/aluminum　joint.　On　this　basis,　the　fluxless　wetting　and　interfacial　reaction　mechanisms　were　revealed.