Résumé
Non-galvanized and 10 µm zinc-coated 1.2 mm thick DC04 steel was joined to 6016-T4 aluminium alloy by using three different laser processses : a key-hole welding mode, with a precise control of the aluminium – steel dilution, a reactive wetting mode where solid steel – liquid aluminium reaction occurred driving to a uniform Fe2Al5 intermetallic layer between the two overlapped sheets and a braze-welding mode involving direct fusion of aluminium and an Al-12Si filler wire on solid steel. For liquid aluminium to liquid steel interactions obtained by key-hole mode, rather sound and resistant assemblies were realized either on non-galvanized or galvanized steel provided steel was placed upon aluminium with penetration in aluminium limited to 0.5 mm. The influence of galvanized layer was only detectable on the fusion zone of aluminium where occluded zinc bubbles were observed. Mechanical resistances of 150 N/mm were obtained for one joint assemblies and could be increased up to 250 N/mm making two joints per assembly. For liquid aluminium to solid steel interactions carried out by defocused laser, 180 N/mm transverse tensile strengths were obtained on non-galvanized steels by using a brazing flux. Due to a better wetting on non-galvanized steels, good assemblies could be obtained without using flux leading to lower mechanical resistances of up to 140 N/mm. However, using flux conduced to 220 N/mm maximal mechanical resistance. For this kind of interaction solid/liquid), using an Al-12Si filler wire allows to obtained also 180 N/mm mechanical strengths on non-galvanized steels using a brazing flux. Same characteristics are obtained in the reaction layers composition with a decrease in maximal layer thickness under 1 µm compared to the 2-40 µm thickness obtained without filler wire. Finally, comparisons are made between the three processes investigated focusing on the mechanical properties and the robustness of each process.